  The best roots are those which have the size of a writing quill, or, at most, of the little finger. They are semitransparent, and reddish; have a strong odour, and a smooth bark. They should be of two or three years’ growth. The madder, taken from the ground and picked, must be dried in order to be ground and preserved. In warm climates it is dried in the open air; but, elsewhere, stoves must be employed. The stringy filaments and epidermis are to be removed, called mulle; as also the pith, so as to leave nothing but the ligneous fibres. The preparation of madders is carried on in the department of the Rhone, in the following manner. The roots are dried in a stove, heated by means of a furnace, from which the air is allowed to issue only at intervals, at the moment when it is judged to be saturated with moisture. The furnace-flue occupies a great portion of the floor; above are three close gratings, on which the roots are distributed in layers of about two decimetres (nearly 8 inches). At the end of 24 hours, those which are on the first grated floor directly above the stove are dry, when they are taken away and replaced by those of the superior floors. This operation is repeated whenever the roots over the stove are dry. The dry roots are thrashed with a flail, passed through fanners similar to those employed for corn, and then shaken upon a very coarse sieve. What passes through is farther winnowed and sifted through a finer sieve than the first. These operations are repeated five times, proceeding successively to sieves still finer and finer, and setting aside every time what remains on the sieve. What passes through the fifth sieve is rejected as sand and dust. After these operations, the whole fibrous matters remaining on the sieve are cleaned with common fanners, and women separate all the foreign matters which had not been removed before. For dividing the roots, afterwards, into different qualities, a brass sieve is made use of, whose meshes are from six to three millimetres in diameter (from 1/4th to 1/8th inch E.) What passes through the finest is rejected; and what passes through the coarsest is regarded as of the best quality. These roots thus separated, are carried into a stove, of a construction somewhat different from the first. They are spread out in layers of about a decimetre in thickness (nearly 4 inches E.), on large lattice-work frames, and the drying is known to be complete, when on taking up a handful and squeezing it, the roots break easily. On quitting the stove, the madder is carried, still hot, into a machine, where it is minced small, and a sieve separates the portion of the bark reduced to powder. This operation is repeated three or four times, and then the boulter is had recourse to. What passes through the sieve, or the brass meshes of the boulter, is regarded as common madder; and what issues at the extremity of the boulter is called the flour. Lastly, the madder which passes through the boulter is ground in a mill with vertical stones, and then passed through sieves of different sizes. What remains above is always better than what goes through. The madder of Alsace is reduced to a very fine powder, and its colouring matter is extracted by a much longer ebullition than is necessary for the lizari of the Levant. The prepared madders ought to be carefully preserved from humidity, because they easily imbibe moisture, in which case fermentation spoils their colour. D’Ambourney and Beckman have asserted, that it is more advantageous to employ the fresh root of madder than what has been submitted to desiccation, especially by means of stoves. But in its states of freshness, its volume becomes troublesome in the dyeing bath, and uniform observation seems to prove that it ameliorates by age. Besides, it must be rendered susceptible of keeping and carrying easily. It appears that madder may be considered as composed of two colouring substances, one of which is dun (tawny), and the other is red. Both of these substances may combine with the stuff. It is of consequence, however, to fix only the red part. The dun portion appears to be more soluble, but its fixity on stuffs may possibly be increased by the affinity which it has for the red portion. The different additions made to madder, and the multiplied processes to which it is sometimes exposed, have probably this separation for their chief object. The red portion of madder is soluble, but in small quantity, in water. Hence but a limited concentration can be given to its solution. If the portion of this substance be too much increased, so far from obtaining a greater effect, we merely augment the proportion of the dun part, which is the more soluble of the two. In consequence of the SociÉtÉ Industrielle of Mulhausen having offered in the year 1826 large premiums to the authors of the best analytical investigation of madder, eight memoirs were transmitted to it in the year 1827. They were examined with the greatest care by a committee consisting of able scientific and practical men. None of the competitors however fulfilled the conditions of the programme issued by the society; but four of them received a tribute of esteem and gratitude from it; MM. Robiquet and Colin at Paris, Kuhlmann at Lille, and Houton-LibillardiÈre. Fresh premiums were offered for next year, to the amount of 2000 francs. Every real discovery made concerning this precious root, would be of vast consequence to dyers and calico-printers. Both M. Kuhlmann, and Robiquet and Colin, conceived that they had discovered a new principle in madder, to which they gave the name alizarine. The latter two chemists treated the powdered madder with sulphuric acid, taking care to let it heat as little as possible. By this action the whole is carbonized, except perhaps the red matter. The charcoal thus obtained is pulverized, mixed with M. Dan. Koechlin, the justly celebrated calico-printer of Mulhausen, has no faith in alizarine as the dyeing principle of madder; and thinks moreover that, were it of value, it could not be extracted on the great scale, on account of the destructive heat which would result from the acid acting upon a considerable body of the ground madder. Their alizarine is not a uniform substance, as it ought to be, if a proximate principle; for samples of it obtained in different repetitions of the process have produced very variable effects in dyeing. The madders of Avignon, though richer in colour than those of Alsace, afford however little or no alizarine. In fact, purpurine, the crude substance from which they profess to extract alizarine, is a richer dye than this pure substance itself. Madder contains so beautiful and so fast a colour, that it has become of almost universal employment in dyeing; but that colour is accompanied with so many other substances which mask and degrade it, that it can be brought out and fixed only after a series of operations more or less difficult and precarious. This dye is besides so little soluble, that much of it is thrown away in the dye-house; the portion supposed to be exhausted being often as rich as other fresh madder; hence it would be a most valuable improvement in this elegant art to insulate this tinctorial body, and make it a new product of manufacture. Before the time of Haussmann, an apothecary at Colmar, the madder bath was subject to many risks, which that skilful chemist taught dyers how to guard against, by introducing a certain quantity of chalk into the bath. A change of residence led Haussmann to this fortunate result. After having made very fine reds at Rouen, he encountered the greatest obstacles in dyeing the same reds at Logelbach near Colmar, where he went to live. Numerous trials, undertaken with the view of obtaining the same success in his new establishment, proved that the cause of his favourable results at Rouen existed in the water, which contained carbonate of lime in solution, whilst the water of Logelbach was nearly pure. He then tried a factitious calcareous water, by adding chalk to his dye bath. Having obtained the most satisfactory results, he was not long of producing here as beautiful and as solid reds as he had done at Rouen. This practice became soon general among the calico-printers of Alsace, though in many dye-works the chalk is now replaced by lime, potash, or soda. But when the madder of Avignon is used, all these antacid correctives become unnecessary, because it contains a sufficient quantity of carbonate of lime; an important fact first analytically demonstrated by that accurate chemist M. Henri Schlumberger of Mulhausen. Avignon madder indicates the presence of carbonate of lime in it, by effervescing with dilute acids, which Alsace madder does not. M. Kuhlmann found a free acid resembling the malic, in his analysis of madders. But his experiments were confined to those of Alsace. The madders of Avignon are on the contrary alkaline, as may be inferred from the violet tint of the froth of their infusions; whereas that of the Alsace madders is yellowish, and it strongly reddens litmus paper. This important difference between the plants of these two districts, depends entirely upon the soil; for madders grown in a calcareous shelly soil in Alsace, have been found to be possessed of the properties of the Avignon madder. The useful action of the carbonate and the phosphate of lime in the madder of Avignon, explains why madders treated with acids which remove their calcareous salts, without taking away their colouring matter, lose the property of forming fast dyes. Many manufacturers are in the habit of mixing together, and with advantage, different sorts of madder. That of Avignon contains so much calcareous matter that, when mixed with the madder of Alsace, it can compensate for its deficiency. Some of the latter is so deficient as to afford colours nearly as fugitive as those of Brazil wood and quercitron. The Alsace madders by the addition of chalk to their baths, become as fit for dyeing Turkey reds as those of Avignon. When the water is very pure, one part of chalk ought to be used to five of Alsace madder, but when the waters are calcareous, the chalk should be omitted. Lime, the neutral phosphate of lime, the carbonate of magnesia, oxide and carbonate of zinc, and several other substances have the property of causing madder to form a fast dye, in like manner as the carbonate of lime. The temperature of from 50° to 60° R. (145° to 167° F.), is the best adapted to the solution of the colouring matter, and to its combination with the mordants; and thus a boiling heat may be replaced advantageously by the long continuance of a lower temperature. A large excess of the dye-stuff in the bath is unfavourable in two points of view; it causes a waste of colouring matter, and renders the tints dull. It is injurious to allow the bath to cool, and to heat it again. In a memoir published by the Society of Mulhausen, in September, 1835, some interesting experiments upon the growth of madders in factitious soils are related by MM. Koechlin, Persoz, and Schlumberger. A patch of ground was prepared containing from 50 to 80 per cent. of chalky matter, and nearly one fifth of its bulk of good horse-dung. Slips of Alsace and Avignon madders were planted in March, 1834, and a part of the roots were reaped in November following. These roots, though of only six months growth, produced tolerably fast dyes, nor was any difference observable between the Alsace and the Avignon species; whilst similar slips or cuttings, planted in a natural non-calcareous soil, alongside of the others, yielded roots which gave fugitive dyes. Others were planted in the soil of Palud, transported from Avignon, which contained more than 90 per cent. of carbonate of lime, and they produced roots that gave still faster dyes than the preceding. Three years are requisite to give the full calcareous impregnation to the indigenous madders of Avignon. As to the function of the chalk, valuable observations, made long ago by M. Daniel Koechlin, have convinced him, that the combination of two different bases with a colouring matter, gave much more solidity to the dye, in consequence, undoubtedly, of a greater insolubility in the compound. Experiments recently made by him and his colleagues above named, prove that in all cases of madder-dyeing under the influence of chalk, a certain quantity of lime becomes added to the aluminous mordant. In the subsequent clearing with a soap bath, some of the alumine is removed, and there remains upon the fibre of the cloth a combination of these two earths in atomic proportions. Thus the chalk is not for the purpose of saturating the acid, as had been supposed, but of forming a definite compound with alumina, and probably also with the fatty bodies, and the colouring matter itself. The red mordants are prepared commonly in Alsace, as follows:—The crushed alum and acetate of lead being weighed, the former is put into a deep tub, and dissolved by adding a proper quantity of hot water, when about one tenth of its weight of soda crystals is introduced to saturate the excess of acid in the alum. The acetate of lead is now mixed in; and as this salt dissolves very quickly, the reaction takes place almost instantly. Care must be taken to stir for an hour. The vessel should not be covered, lest its contents should cool too slowly. The different mordants most generally employed for madder, are detailed under Colours, in Calico-Printing and Mordant. Much mordant should not be prepared at once, for sooner or later it will deposit some sub-acetate of alumina. This decomposition takes place even in corked phials in the cold; and the precipitate does not readily dissolve again in acetic acid. All practical men know that certain aluminous mordants are decomposed by heating them, and restored on cooling, as Gay Lussac has pointed out. He observed, that by adding to pure acetate of alumina, some alum or sulphate of potash, the mixture acquires the property of forming a precipitate with a heat approaching the boiling point, and of redissolving on cooling. The precipitate is alumina nearly pure, according to M. Gay Lussac; but, by M. Koechlin’s more recent researches, it is shown to be sub-sulphate of alumina, containing eight times as much base as the neutral sulphate. Madder dye.—On account of the feeble solubility of its colouring matter in water, we cannot dye with its decoction; but we must boil the dye-stuff along with the goods to be dyed; thereby the water dissolves fresh portions of the dye, and imparts it in succession to the textile fibres. In dyeing with madder, we must endeavour to fix as little of the dun matter as possible upon the cloth. Dyeing on wool.—Alumed wool takes, in the madder bath, a red colour, which is not so bright as cochineal red, but it is faster; and as it is far cheaper, it is much used in England to dye soldiers cloth. A mordant of alum and tartar is employed; the bath of madder, at the rate of from 8 to 16 ounces for the pound of cloth, is heated to such a degree that we can just hold our hand in it, and the goods are then dyed by the wince, without heating the bath more till the colouring matter be fixed. Vitalis prescribes as a mordant, one fourth of alum, and one sixteenth of tartar; and for dyeing, one third of madder, with the addition of a 24th of solution of tin diluted with its weight of water. He raises the temperature in the space of an hour, to 200°, and afterwards he boils for 3 or 4 minutes; a circumstance which is believed to contribute to the fixation of the colour. The bath, after dyeing, appears much loaded with yellow matter, because this has less affinity for the alum mordant than the red. Sometimes a little archil is added to the madder, to give the dye a pink tinge; but this is fugitive. Silk is seldom dyed with madder, because cochineal affords brighter tints. Dyeing on cotton and linen.—The most brilliant and fastest madder red is the Turkey or Adrianople. The common madder reds are given in the following way:—The yarn or cloth is boiled in a weak alkaline bath, washed, dried and galled, by steeping the cotton in a decoction of bruised galls or of sumach. After drying, it is twice alumed; for which purpose, for every 4 parts of the goods, one part of alum is taken, mixed with 1-16th of its weight of chalk. The goods are dipped into a warm solution of the alum, wrung out, dried, and alumed afresh, with half the quantity. The acetate of alumina mordant, described above, answers much better than common alum for cotton. After the goods are dried and rinsed, they are passed through the dye bath, which is formed of 3/4 lb. of good madder for every pound of cotton; and it is raised to the boiling point by degrees, in the space of 50 or 60 minutes. Whenever the ebullition has continued a few minutes, the goods must be removed, washed slightly, and dyed a second time in the same way, with as much madder. They are then washed and passed through a warm soap bath, which removes the dun colouring matter. HÖlterhoff prescribes for ordinary madder red the following proportions:—20 pounds of cotton yarn; 14 pounds of Dutch madder; 3 pounds of nut-galls; 5 pounds of alum; to which 1/2 lb. of acetate of lead has been first added, and then a quarter of a pound of chalk. In the calico-print works the madder goods are passed through a bran bath first, immediately after dyeing; next, after several days exposure to the air, when the dun dye has become oxidized, and is more easily removed. An addition of chalk, on the principles explained above, is sometimes useful in the madder bath. If bran be added to the madder bath, the colour becomes much lighter, and of an agreeable shade. Sometimes bran-water is added to the madder bath, instead of bran. Adrianople or Turkey red.—This is the most complicated and tedious operation in the art of dyeing; but it produces the fastest colour which is known. This dye was discovered in India, and remained long a process peculiar to that country. It was afterwards practised in other parts of Asia and in Greece. In 1747, Ferquet and Goudard brought Greek dyers into France, and mounted near Rouen, and in Languedoc, Turkey-red dye works. In 1765, the French government, convinced of the importance of this business, caused the processes to be published. In 1808, Reber, at Mariakirch, furnished the finest yarn of this dye, and M. KÖchlin became celebrated for his Turkey-red cloth. Process for Turkey-red.—The first step consists in clearing the yarn or cloth in alkaline baths, and dipping them in oily liquors, to which sheep’s dung was formerly added. This operation is repeated several times, the goods being dried after each immersion. There next follows the cleansing with alkaline liquors to remove the excess of oil, the galling, the aluming, the maddering, the brightening or removing the dun part of the dye by boiling, at a high temperature, with alkaline liquid, and the rosing by boiling in a bath of salt of tin. We shall give some details concerning this tedious manipulation, and the differences which exist in it in the principal dye-works. At Rouen, where the process was first brought to perfection, two methods are pursued, called the gray and the yellow course or march. In the gray, the dye is given immediately after the cotton has received the oily mordant, the gall, and the alum, as it has then a gray colour. In the yellow course, it is passed through fresh oils, alum, and galls before the maddering, the cotton having then a yellow tint. Different views have been taken of the principles of the Turkey red dye, and the object and utility of the various steps. The most ancient notion is that of animalizing the cotton by dung and blood, but experience has proved that without any animal matter the finest colour may be obtained. According to Dingler, the cotton is imbued with oil by steeping it in combinations of oil and soda; the oil is altered by repeated dryings at a high temperature; it attracts oxygen from the air, and thereby combines intimately with the cotton fibre, so as to increase the weight of the stuff. The dung, by a kind of fermentation, accelerates the oxidizement, and hence crude oil is preferable to pure. In England, the mucilaginous oils of Gallipoli are preferred, and in Malabar, oils more or less rancid. The drying oils do not answer. The subsequent treatment with the alkaline liquors removes the excess of oil, which has not been oxidized and combined; a hard drying completely changes that which remains in the fibres; the aluming which follows combines alumina with the cotton; the galling tans the fibres, producing a triple compound of oil and alum, which fixes the colouring matter. The object of the other steps is obvious. According to Wuttich the treatment with oil opens the cotton so as to admit the mordant and the colouring matter, but the oil and soap do not combine with the fibres. In the alkaline baths which follow, the oil is transformed into soap and removed; whence the cotton should not increase in weight in the galling and aluming; the cotton The German process improved, according to Dingler, consists of the following operations: mordant of an oily soap or a soapy liniment, hard drying; alkaline bath, drying, steeping, rinsing away of the uncombined mordant, drying; galling, drying; aluming, drying, steeping in water containing chalk, rinsing; maddering, airing, rinsing; brightening with an alkaline boil, and afterwards in a bath containing salt of tin; then washing and drying. The yarn or the cloth must be first well worked in a bath of sheep’s dung and oil, compounded as follows:—25 pounds of sheep’s dung are to be bruised in a solution of pure caustic potash of hydrometer strength 3°, and the mixed liquor is to be passed through a sieve. Two pounds of fine oil are now to be poured into 16 pounds of this lye, after which 30 pounds of coarse oil are to be added, with agitation for 1/4 of an hour. Other 4 pounds of hot lye are to be well stirred in, till the whole is homogeneous. This proportion of mordant is sufficient for 100 pounds of cotton yarn, for 90 pounds of unbleached or 100 pounds of bleached cotton goods. The cotton stuff, after being well wrung out, is to be laid in a chest and covered with a lid loaded with weights, in which state it should remain for five days. At the end of 24 hours, the cotton becomes hot with fermentation, gets imbued with the mordant, and the oil becomes rapidly altered. The goods are next exposed freely to the air during the day, and in the evening they are dried in a hot chamber, exposed to a temperature of 158° F., for 6 or 8 hours, which promotes the oxidizement of the oil. The goods are now passed the second time through a soapy-oil mordant similar to the first, then dried in the air by day, and in the hot stove by night. The third and fourth oil-soap steeps are given in the same way, but without the dung. The fifth steep is composed of a lye at 2°, after which the goods must also be dried. Indeed from the first to the fourth steep, the cotton stuff should be put each time into a chamber heated to 145° F. for 12 or 15 hours, and during 18 hours after the fifth steep. The uncombined oil must, in the next place, be withdrawn by the degraissage, which consists in steeping the goods for 6 hours in a very weak alkaline ley. After rinsing and wringing, they are dried in the air, and then put into the hot stove. The goods are now galled in a bath formed of 36 pounds of Sicilian sumach, boiled for 3 hours in 260 pounds of water, and filtered. The residuum is treated with 190 fresh pounds of water. This decoction is heated with 12 pounds of pounded nut-galls to the boiling point, allowed to cool during the night, and used next morning as hot as the hand can bear; the goods being well worked through it. They are again dried in the air, and afterwards placed in a stove moderately heated. They are next passed through a tepid alum bath, containing a little chalk; left afterwards in a heap during the night, dried in the air, and next in the stove. The dry goods are finally passed through hot water containing a little chalk, wrung out, rinsed, and then maddered. For dyeing, the copper is filled with water, the fire is kindled, and an ounce and a half of chalk is added for every pound of madder; a pound and a quarter of madder being taken for every pound of cotton yarn. The goods are now passed through the bath, so that they penetrate to near its bottom. The fire must be so regulated, that the copper will begin to boil in the course of from 21/2 to 3 hours; and the ebullition must be continued for an hour; after which the yarn is aired and rinsed. Cloth should be put into the dye-bath when its temperature is 77°, and winced at a heat of from 100° to 122° during the first hour; at 167° during the second; and at the boiling point when the third hour begins. It is to be kept boiling for half an hour; so that the maddering lasts four hours. Dingler does not add sumach or galls to the madder bath, because their effect is destroyed in the subsequent brightening, and he has no faith in the utility of blood. After being dyed, the goods are washed, pressed, and subjected to a soapy alkaline bath at a high heat, in a close boiler, by which the dun parts of the galls and the madder are dissolved away, and the red colour remains in all its lustre. This operation is called brightening. It is repeated in a similar liquor, to which some muriate of tin is added for the purpose of enlivening the colour and giving it a rosy tint. Last of all, the goods are rinsed, and dried in the shade. The Elberfeld process consists for 100 libs. of the following steps:— 1. Cleaning the cotton by boiling it for four hours in a weak alkaline bath, cooling and rinsing. 2. Working it thoroughly four times over in a steep, consisting of 300 pounds of water, 15 pounds of potash, 1 pailful of sheep’s dung, and 121/2 pounds of olive oil, in which it should remain during the night. Next day it is drained for an hour, wrung out and dried. This treatment with the dung steep, and drying, is repeated 3 times. 3. It is now worked in a bath containing 120 quarts of water, 18 pounds of potash, 4. Steeping for a night in the river is the next process; a slight rinsing without wringing, and drying in the air. 5. Bath made of a warm decoction (100° F.) of sumach and nut-galls, in which the goods remain during the night; they are then strongly wrung, and dried in the air. 6. Aluming with addition of potash and chalk; wringing; working it well through this bath, where it is left during the night. 7. Draining, and strong rinsing the following day; piling up in a water cistern. 8. Rinsing repeated next day, and steeping in water to remove any excess of alum from the fibres; the goods continue in the water till they are taken to the dyeing-bath. 9. The maddering is made with the addition of blood, sumach, and nut-galls; the bath is brought to the boil in 1 hour and 3/4, and kept boiling for half an hour. 10. The yarn is rinsed, dried, boiled from 24 to 36 hours in a covered copper, with an oily alkaline liquid; then rinsed twice, laid for two days in clear water, and dried. 11. Finally, the greatest brightness is obtained by boiling for three or four hours in a soap bath, containing muriate of tin; after which the yarn is rinsed twice over, steeped in water, and dried. Process of Haussmann.—He treats cotton twice or 4 times in a solution of aluminated potash, mixed with one thirty-eighth part of linseed oil. The solution is made by adding caustic potash to alum. He dries and rinses each time, and dries after the last operation. He then rinses and proceeds to the madder bath. For the rose colour, he takes one pound of madder for one pound of cotton; for carmine red, he takes from 2 to 3 pounds; and for the deepest red, no less than 4 pounds. It is said that the colour thus obtained surpasses Turkey red. The French process, by Vitalis of Rouen.—First operation. Scouring with a soda lye, of 1° BaumÉ, to which there is usually added the remainder of the white preparation bath, which consists of oil and soda with water. It is then washed, wrung out, and dried. In the second operation, he states that from 25 to 30 pounds of sheep’s dung are commonly used for 100 pounds of cotton yarn. The dung is first steeped for some days in a lye of soda, of 8° to 10° B. This is afterwards diluted with about 500 pints of a weaker ley, and at the same time bruised with the hand in a copper basin whose bottom is pierced with small holes. The liquor is then poured into a vat containing 5 or 6 pounds of fat oil (Gallipoli), and the whole are well mixed. The cotton is washed in this, and the hanks of yarn are then stretched on perches in the open air, and turned from time to time, so as to make it dry equably. After receiving thus a certain degree of desiccation, it is carried into the drying house, which is heated to 50° Reaumur (144° Fahrenheit), where it loses the remainder of its moisture, which would have prevented it from combining with the other mordants which it is afterwards to receive. What is left of the bath is called avances, and is added to the following bath. Two, or even three dung baths are given to the cotton, when it is wished to have very rich colours. When the cotton has received the dung baths, care must be taken not to leave it lying in heaps for any length of time, lest it should take fire; an accident which has occasionally happened. The white bath is prepared by pouring 6 pounds of fat oil, into 50 pints of soda water, at 1° or sometimes less, according as, by a preliminary trial, the oil requires. This bath ought to be repeated two, three, or even a greater number of times, as more or less body is to be given to the colour. To what remains of the white bath, and which is also styled avances, about 100 pints of soda lye of two or three degrees are added. Through this the cotton is passed as usual. Formerly it was the practice to give two, or three, or even four oils. Now, two are found to be sufficient. The cotton is steeped for five or six hours in a tepid solution of soda, of 1° at most; it is set to drain, is then sprinkled with water, and at the end of an hour is washed, hank by hank, to purge it entirely from the oil. What remains of the water of degraissage, serves for the scouring or first operation. For 100 pounds of cotton, from 20 to 25 pounds of galls in sorts must be taken, which are bruised and boiled in about 100 pints of water, till they crumble easily between the fingers. The galling may be done at two operations, dividing the above quantity of galls between them, which is thought to give a richer and more uniform colour. The aluming of 100 pounds of cotton requires from twenty-five to thirty pounds of pure alum, that is, alum entirely free from ferruginous salts. The alum should be dissolved without boiling, in about 100 pints of river or rain water. When the alum is dissolved, there is to be poured in a solution of soda, made with the sixteenth part of the weight of the alum. A second portion of the alkaline solution must not be poured in till the effervescence caused by the first portion has entirely ceased,—and For 25 pounds of cotton, 25 pints of blood are prescribed, and 400 pints of water. Whenever the bath begins to warm, 50 pounds of madder are diffused through the bath; though sometimes the maddering is given at two operations, by dividing the madder into two portions. The brightening bath is prepared always for 100 pounds of cotton, with from four to five pounds of rich oil, six pounds of Marseilles white soap, and 600 litres of soda water of 2° B. The rosing is given with solution of tin, mixed with soap water. The Turkey-red dye of Messrs. Monteith and Co., of Glasgow, is celebrated all over the world, and merits a brief description here. The calico is taken as it comes from the loom without bleaching, for the natural colour of the cotton wool harmonizes well with the dye about to be given; it is subjected to a fermentative steep for 24 hours, like that preliminary to bleaching, after which it is washed at the dash wheel. It is then boiled in a lye, containing about 1 pound of soda crystals for 12 pounds of cloth. The oiling process now begins. A bath is made with 10 gallons of Gallipoli oil, 15 gallon measures of sheep’s dung not indurated; 40 gallons of solution of soda crystals, of 1·06 specific gravity; 10 gallons of solution of pearl-ash of spec. grav. 1·04; and 140 gallons of water; constituting a milk-white, soapy solution of about spec. grav. 1·022. This liquor is put into a large cylindrical vat, and constantly agitated by the rotation of wooden vanes, which are best constructed on the plan of the mashing apparatus of a brewery, but far slighter. This saponaceous compound is let off as wanted by a stopcock into the trough of a padding machine, in order to imbue every fibre of the cloth in its passage. This impregnation is still more fully ensured by laying the padded cloth aside in wooden troughs during 16 or 18 days. The sheep’s dung has been of late years disused by many Turkey-red dyers both in England and France, but it is found to be advantageous in producing the very superior colour of the Glasgow establishment. It is supposed, also, to promote the subsequent bleaching during the exposure on the green; which is the next process in favourable weather, but in bad weather the goods are dried over a hot-flue. The cloth is padded again with the saponaceous liquor; and again spread on the grass, or dried hard in the stove. This alternation is repeated a third time, and occasionally, even a fourth. The cloth by this time is varnished as it were with oil, and must be cleansed in a certain degree by being passed through a weak solution of pearl-ash, at the temperature of about 122° F. It is then squeezed by the rollers and dried. A second system of oiling now commences, with the following liquor:—10 gallons of Gallipoli oil; 30 gallons of soda crystals lye, of sp. grav. 1·06; and 10 gallons of caustic potash lye, of specific gravity 1·04, thoroughly diffused through 170 gallons of water. With this saponaceous liquor the cloth is padded as before, and then passed between squeezing-rollers, which return the superfluous liquor into the padding-trough. The cloth may be now laid on the grass if convenient; but at any rate it must be hard dried in the stove. These saponifying, grassing, and drying processes, are repeated three times; whereby the cloth becomes once more very oleaginous, and must be cleansed again by steeping in a compound lye of soda crystals and pearl-ash of the spec. grav. 1·012, at the temperature of 122°. The cloth is taken out, squeezed between rollers to save the liquor, and washed. A considerable portion of the mingled alkalis disappear in this operation, as if they entered into combination with the oil in the interior of the cotton filaments. The cloth is now hard dried. Galling is the next great step in the Turkey-red preparation; and for its success all the oil should have been perfectly saponified. From 18 to 20 pounds of Aleppo galls (for each 100 libs of cloth) are to be bruised and boiled for 3 or 4 hours, in 25 gallons of water, till 5 gallons be evaporated; and the decoction is to be then passed through a searce. Two pounds of sumach may be substituted for every pound of galls. The goods must be well padded with this decoction, kept at 90° F., passed through squeezing-rollers, and dried. They are then passed through a solution of alum of the sp. gr. 1·04, to which a certain portion of chalk is added to saturate the acid excess of that supersalt; and in this cretaceous mixture, heated to 110°, the cloth is winced and steeped for 12 hours. It is then passed between squeezing-rollers, and dried in the stove. The maddering comes next. From two to three pounds of madder, ground to powder in a proper mill, are taken for every pound of cloth. The cloth, as usual in maddering, is entered into the cold As madder contains a dingy brown colouring matter associated with the fine red, the goods must be subjected to a clearing process to remove the former tinge, which is more fugitive than the latter. Every hundred pounds of cloth are therefore boiled during 12 hours at least, with water containing 5 pounds of soda crystals, 8 pounds of soap, and 16 gallons of the residual pearl-ash and soda-lye of the last cleansing operation. By this powerful means the dun matter is well nigh removed; but it is completely so by a second boil, at a heat of 250° F., in a tight globular copper, along with 5 pounds of soap, and 1 pound of muriate of tin crystals, dissolved in a sufficient body of water for 100 pounds of cloth. The muriate of tin serves to raise the madder red to a scarlet hue. A margarate of tin is probably fixed upon the cloth in this operation. When the weather permits, the goods should be now laid out for a few days on the grass. Some manufacturers give them a final brightening with a weak bath of a chloride of lime; but it is apt to impoverish the colour. According to the latest improvements of the French dyers, each of the four processes of oiling, mordanting, dyeing, and brightening differs, in some respects, from the above. 1. Their first step is boiling the cloth for four hours, in water containing one pound of soap for every four pieces. Their saponaceous bath of a creamy aspect is used at a temperature of 75° F.; and it is applied by the padding machine 6 times, with the grassing and drying alternations. In winter, when the goods cannot be exposed on the grass, no less than 12 alternations of the saponaceous or white bath are employed, and 8 in spring. They consider the action of the sun-beam to aid greatly in brightening this dye; but at Midsummer, if it be continued more than 4 hours, the scarlet colour produced begins to be impaired. They conceive that the oiling operation impregnates the fibres with super-margarate of potash or soda, insoluble salts which attract and condense the alumina, and the red colouring particles of the madder, so firmly that they can resist the clearing boil. 2. Their second step, the mordanting, consists first in padding the pieces through a decoction of galls mixed with a solution of an equal weight of alum; and after drying in the hot-flue, &c., again padding them in a solution of an acetate of alumina, made by decomposing a solution of 16 libs. of alum with 16 libs of acetate of lead, for 6 pieces of cloth, each 32 aunes long. 3. The maddering is given at two successive operations; with 4 pounds of Avignon madder per piece at each time. 4. The brightening is performed by a 12 hours’ boil in water with soda crystals, soap, and salt of tin; and the rosing by a 10 hours’ boil with soap and salt of tin. Occasionally, the goods are passed through a weak solution of chloride of potash. When the red has too much of a crimson cast, the pieces are exposed for two days on the grass, which gives them a bright scarlet tint. Process of M. Werdet to dye broad cloth and wool by madder:— “Preparation for 24 pounds of scoured wool: “Take 41/4 pounds of cream of tartar, 41/4 pounds of pure alum; boil the wool gently for 2 hours, transfer it into a cool place, and wash it next day in clear water. “Dyeing.—12 pounds of Avignon madder, infused half an hour at 30° R. (100° F.) Put into the bath 1 pound of muriate of tin, let the colour rose for three quarters of an hour at the same heat, and drain or squeeze the madder through canvas. The whole of the red dye will remain upon the filter, but the water which has passed through will be as deep a yellow as a weld bath. The boiler with the dye must now be filled up with clear river water, and heated to 100° F. Two ounces of the solution of the tartar and alum must be poured into it, and the wool must be turned over in it for an hour and a half, while the heat is gradually raised to the boiling point. The wool is then removed and washed. It must be rosed the following day. “Rosing.—Dissolve in hot water 1 pound of white Marseilles soap; let the bath cool, and pass the wool through it till it has acquired the desired shade; 15 or 20 minutes are sufficient. On coming out of this bath it should be washed. “Solution of deuto-muriate of tin:— “2 ounces of pure muriatic acid; 4 drachms of pure nitric acid; 1 ounce of distilled water. Dissolve in it, by small portions at a time, 2 drachms of grain tin, in a large bottle of white glass, shutting it after putting in the tin. This solution may be preserved for years, without losing its virtue.” I have inserted this process, as recently recommended by the French minister of commerce,
Magnesia may be obtained by precipitation with potash or soda, from its sulphate, commonly called Epsom salt; but it is usually procured by calcining the artificial or natural carbonate. The former is, properly speaking, a subcarbonate, consisting of 44·69 magnesia, 35·86 carbonic acid, and 19·45 water. It is prepared by adding to the solution of the sulphate, or the muriate (the bittern of sea-salt evaporation works), a solution of carbonate of soda, or of carbonate of ammonia distilled from bones in iron cylinders. The sulphate of magnesia is generally made by acting upon magnesian limestone with somewhat dilute sulphuric acid. The sulphate of lime precipitates, while the sulphate of magnesia remains in solution, and may be made to crystallize in quadrangular prisms, by suitable evaporation and slow cooling. Where muriatic acid may be had in profusion for the trouble of collecting it, as in the soda works in which sea salt is decomposed by sulphuric acid, the magnesian limestone should be first acted upon with as much of the former acid as will dissolve out the lime, and then, the residuum being treated with the latter acid, will afford a sulphate at the cheapest possible rate; from which magnesia and all its other preparations may be readily made. Or, if the equivalent quantity of calcined magnesian limestone be boiled for some time in bittern, the lime of the former will displace the magnesia from the muriatic acid of the latter. This is the most economical process for manufacturing magnesia. The subcarbonate, or magnesia alba of the apothecary, has been proposed by Mr. E. Davy to be added by the baker to damaged flour, to counteract its acescency. Massive magnesian limestone, is yellowish-brown, cream-yellow, and yellowish-gray; brittle. It dissolves slowly and with feeble effervescence in dilute muriatic acid; whence Near Sunderland, it is found in flexible slabs. The principal range of hills composing this geological formation in England, extends from Sunderland on the northeast coast to Nottingham, and its beds are described as being about 300 feet thick on the east of the coal field in Derbyshire, which is near its southern extremity. On the western side of the Cumberland mountains magnesian limestone overlies the coal measures near Whitehaven. The stratification of this rock is very distinct, the individual courses of stone not exceeding in general the thickness of a common brick. The lime resulting from the calcination of magnesian limestone appears to have an injurious action on vegetation, unless applied in quantities considerably less than common lime, when it is found to fertilize the soil. After two years, its hurtful influence on the ground seems to become exhausted, even when used in undue quantity. Great quantities of it are annually brought from Sunderland to Scotland by the Fifeshire farmers, and employed beneficially by them, as a manure, in preference to other kinds of lime. It has been unfairly denounced by Mr. Tennent and Sir H. Davy, as a sterilizer. This rock is used in many places for building; indeed our most splendid monument of Gothic architecture, York Minster, is constructed of magnesian limestone. The acid may be obtained most conveniently from the juice of the berries of the mountain ash, or barberries. This must be clarified, by mixing with white of egg, and heating the mixture to ebullition; then filtering, digesting the clear liquor with carbonate of lead, till it becomes neutral; and evaporating the saline solution, till crystals, of malate of lead be obtained. These are to be washed with cold water, and purified by re-crystallization. On dissolving the white salt in water, and passing a stream of sulphuretted hydrogen through the solution, the lead will be all separated in the form of a sulphuret, and the liquor, after filtration and evaporation, will yield yellow granular crystals, or cauliflower concretions, of malic acid, which may be blanched by re-dissolution and digestion with bone-black, and re-crystallization. Malic acid has no smell, but a very sour taste, deliquesces by absorption of moisture from the air, is soluble in alcohol, fuses at 150° Fahr., is decomposed at a heat of 348°, and affords by distillation a peculiar acid, the pyromalic. It consists in 100 parts, of 41·47 carbon; 3·51 hydrogen; and 55·02 oxygen; having nearly the same composition as citric acid. A crude malic acid might be economically extracted from the fruit of the mountain ash, applicable to many purposes; but it has not hitherto been manufactured upon the great scale. Table of the Quantity of Malt consumed by the undermentioned Brewers of London and Vicinity, from October 10th, 1836, to October 10th, 1837.
Table of the Quantity of Malt from Barley, which paid Duty in
Manganese is susceptible of five degrees of oxigenation:— 1. The protoxide may be obtained from a solution of the sulphate by precipitation with carbonate of potash, and expelling the carbonic acid from the washed and dried carbonate, by calcination in a close vessel filled with hydrogen gas, taking care that no air have access during the cooling. It is a pale green powder, which slowly attracts oxygen from the air, and becomes brown; on which account it should be kept in glass tubes, containing hydrogen, and hermetically sealed. It consists of 77·57 metal and 22·43 oxygen. It forms with 24 per cent. of water a white hydrate; and with acids, saline compounds; which are white, pink, or amethyst coloured. They have a bitter, acerb taste, and afford with hydrogenated sulphuret of ammonia, a flesh-red precipitate, but with caustic alkalis, one which soon turns brown-red, and eventually black. 2. The deutoxide of manganese exists native in the mineral called Braunite; but it may be procured either by calcining, at a red heat, the proto-nitrate, or by spontaneous oxidizement of the protoxide in the air. It is black; when finely pulverized, dark brown, and is convertible, on being heated in acids, into protoxide, with disengagement of oxygen gas. It consists of 69·75 metal, and 30·25 oxygen. It forms with 10 per cent. of water, a liver-brown hydrate, which occurs native under the name of Manganite. It dissolves readily in tartaric and citric acids, but in few others. This oxide constitutes a bronze ground in calico-printing. 3. Peroxide of manganese; Braunstein, occurs abundantly in nature. It gives out oxygen freely when heated, and becomes an oxidulated deutoxide. It consists of 63·36 metal, and 36·64 oxygen. 4. Manganesic acid, forms green-coloured salts, but has not hitherto been insulated from the bases. It consists of 53·55 metal, and 46·45 oxygen. 5. Hypermanganesic acid, consists of 49·70 metal, and 50·30 oxygen. Ores of manganese.—There are two principal ores of this metal which occur in great masses; the peroxide and the hydrated oxide; the first of which is frequently found in primitive formations. 1. Metalloide oxide of manganese; pyrolusite, or gray manganese ore; has a metallic lustre, a steel gray colour, and affords a black powder. Spec. grav. 4·85. Scratches calc-spar. It effervesces briskly with borax at the blow-pipe, in consequence of the disengagement of oxygen gas. This is the most common ore of manganese, and a very valuable one, being the substance mostly employed in the manufacture of chloride of lime and of flint-glass. It is the peroxide. Great quantities are found near Tavistock, in Devonshire, and Launceston, in Cornwall. 2. Braunite, is a dark brown substance, of a glassy metallic lustre, affording a brown powder. Spec. grav. 4·8. It scratches felspar; but is scratched by quartz. Infusible at the blow-pipe, and effervesces but slightly when fused with glass of borax. It is the deutoxide. It gives out at a red heat only 3 per cent. of oxygen. 3. Manganite, or hydroxide of manganese; is brownish-black or iron-black, powder brown, with somewhat of a metallic lustre. Spec. grav. 4·3. Scratches fluor spar; affords water by calcination in a glass tube; infusible at the blow-pipe; and effervesces slightly when fused with glass of borax. It consists of about 90 of deutoxide, and 10 of water. 4. Haussmanite, black braunstein; is brownish-black, affords a reddish-brown powder. Spec. grav. 4·7; scratches fluor spar; infusible at the blow-pipe; does not effervesce when fused with borax. It is a deutoxide. This is a rare mineral, and of no value to the arts. 5. Barytic oxide of manganese; fibrous wad. It is a combination of deutoxide and peroxide, with some baryta. 6. Manganese blende, or sulphuret of manganese; has a metallic aspect; is black, or dark steel gray; spec. grav. 3·95; has no cleavage; cannot be cut; infusible, but affords after being roasted distinct evidence of manganese, by giving a violet tinge to soda at the blow-pipe. Soluble in nitric acid; solution yields a white precipitate with the ferro-cyanide of potassium. It consists of sulphur 53·65; manganese 66·35. 7. Carbonate of manganese; dialogite. Spec. grav. 3·4; affords a green frit by fusion with carbonate of soda; is soluble with some effervescence in nitric acid; solution when freed from iron by succinate of ammonia, gives a white precipitate, with ferrocyanide of potassium. It consists of 28 carbonic acid, 56 protoxide of manganese, 5·4 of lime, 4·5 protoxide of iron, and 0·8 magnesia. 8. Hydrosilicate of manganese; is a black metallic looking substance, which yields a yellowish-brown powder, and water by calcination; is acted upon by muriatic acid, but affords no chlorine. It consists of silica 25; protoxide of manganese 60; water 13. 9. Ferriferous phosphate of manganese, is brown or black. Spec. grav. 3·6; scratches fluor; affords by calcination a very little of an acid water which corrodes glass; very fusible at the blow-pipe into a black metalloid magnetic bead; is acted upon by nitric acid: solution lets fall a blue precipitate with ferrocyanide of potassium; which tested by soda is shown to be manganese. It consists of phosphoric acid 32·78; protoxide of iron 31·90; protoxide of manganese 32·60; phosphate of lime 3·2. Another phosphate called hureaulite, contains 38 of phosphoric acid; 11·10 of protoxide of iron; 32·85 of protoxide of manganese, and 18 of water. Black wad, is the old English name of the hydrated peroxide of manganese. It occurs in various imitative shapes, in froth-like coatings upon other minerals, as also massive. Some varieties possess imperfect metallic lustre. The external colour is brown of various shades, and similar in the streak, only shining. It is opaque, very sectile, soils and writes. Its specific gravity is about 3·7. Mixed with linseed oil into a dough, black wad forms a mass that spontaneously inflames. A variety from the Hartz, analyzed by Klaproth, afforded peroxide of manganese 68; oxide of iron 6·5; water 17·5; carbon 1; barytes and silica 9. The localities of black wad are particularly Cornwall and Devonshire, the Hartz, and Piedmont. I have analyzed many varieties of the black wad sold to the manufacturers of bleaching salt, and flint glass, and have found few of them so rich in peroxide of manganese as the above. Very generally they contained no less than 25 per cent. of oxide of iron, 8 or 9 of silica, about 7 of water, and the remainder amounting to only 60 per cent. of the peroxide. M. Gay Lussac has proposed to determine the commercial value of manganese ore, by the quantity of chlorine which it affords when treated with liquid muriatic acid. He places the manganese powder in a small retort or matras, pours over it the acid, and the chlorine being disengaged with the aid of a gentle heat, is transmitted into a vessel containing milk of lime or potash water. This liquor is thereafter poured into a dilute The manufacturer of flint glass uses a small proportion of the black manganese ore, to correct the green tinge which his glass is apt to derive from the iron present in the sand he employs. To him it is of great consequence to get a native manganese containing as little iron oxide as possible; since in fact the colour or limpidity of his product will depend altogether upon that circumstance. Sulphate of manganese has been of late years introduced into calico printing, to give a chocolate or bronze impression. It is easily formed by heating the black oxide, mixed with a little ground coal, with sulphuric acid. See Calico Printing. The peroxide of manganese is used also in the formation of glass pastes, and in making the black enamel of pottery. See Oxalic Acid. Mr. Warcup, of Dartford, obtained a patent several years ago for a mangle, in which the linen, being rolled round a cylinder revolving in stationary bearings, is pressed downwards by heavy weights hung upon its axes, against a curved bed, made to slide to and fro, or traverse from right to left, and left to right, alternately. Mr. Hubie, of York, patented in June, 1832, another form of mangle, consisting of three rollers, placed one above another in a vertical frame, the axle of the upper roller being pressed downwards by a powerful spring. The articles intended to be smoothed are introduced into the machine by passing them under the middle roller, which is made to revolve by means of a fly wheel; the pinion upon whose axis works in a large toothed wheel fixed to the shaft of the same roller. The linen, &c. is lapped as usual in protecting cloths. This machine is merely a small Calender. Marble effervesces with acids; affords quicklime by calcination; has a conchoidal scaly fracture; is translucent only on the very edges; is easily scratched by the knife; has a spec. grav. of 2·7; admits of being sawn into slabs; and receives a brilliant polish. These qualities occur united in only three principal varieties of limestone; in the saccharoid limestone, so called from its fine granular texture resembling that of loaf sugar, and which constitutes modern statuary marble, like that of Carrara; 2. in the foliated limestone, consisting of a multitude of small facets formed of little plates applied to one another in every possible direction, constituting the antique statuary marble, like that of Paros; 3. in many of the transition and carboniferous, or encrinitic limestones, subordinate to the coal formation. The saccharoid and lamellar, or statuary marbles, belong entirely to primitive and transition districts. The greater part of the close-grained coloured marbles belong also to the same geological localities; and become so rare in the secondary limestone formations, that immense tracts of these occur without a single bed sufficiently entire and compact to constitute a workable marble. The limestone lying between the calcareo-siliceous sands and gritstone of the under oolite, and which is called Forest marble in England, being susceptible of a tolerable polish, and variegated with imbedded shells, has sometimes been worked into ornamental slabs in Oxfordshire, where it occurs in the neighbourhood of Whichwood forest; but this case can hardly be considered as an exception to the general rule. To constitute a profitable marble-quarry, there must be a large extent of homogeneous limestone, and a facility of transporting the blocks after they are dug. On examining these natural advantages of the beds of Carrara marble, we may readily understand how the statuary marbles discovered in the Pyrenees, Savoy, Corsica, &c. have never been able to come into competition with it in Gypseous alabaster may be readily distinguished from marbles, because it does not effervesce with acids, and is soft enough to be scratched by the nail; stalagmitic alabaster is somewhat harder than marble, translucent, and variegated with regular stripes or undulations. Some granular marbles are flexible in thin slabs, or, at least, become so by being dried at the fire; which shews, as Dolomieu suspected, that this property arises from a diminution of the attractive force among the particles, by the loss of the moisture. The various tints of ornamental marbles generally proceed from oxides of iron; but the blue and green tints are sometimes caused by minute particles of hornblende, as in the slate-blue variety called Turchino, and in some green marbles of Germany. The black marbles are coloured by charcoal, mixed occasionally with sulphur and bitumen; when they constitute stinkstone. Brard divides marbles, according to their localities, into classes, each of which contains eight subdivisions:— 1. Uni-coloured marbles; including only the white and the black. 2. Variegated marbles; those with irregular spots or veins. 3. Madreporic marbles, presenting animal remains in the shape of white or gray spots, with regularly disposed dots and stars in the centre. 4. Shell marbles; with only a few shells interspersed in the calcareous base. 5. Lumachella marbles, entirely composed of shells. 6. Cipolin marbles, containing veins of greenish talc. 7. Breccia marbles, formed of a number of angular fragments of different marbles, united by a common cement. 8. Puddingstone marbles; a conglomerate of rounded pieces. Antique marbles.—The most remarkable of these are the following:—Parian marble, called lychnites by the ancients, because its quarries were worked by lamps; it has a yellowish-white colour; and a texture composed of fine shining scales, lying in all directions. The celebrated Arundelian tables at Oxford consist of Parian marble, as well as the Medicean Venus. Pentelic marble, from Mount Penteles, near Athens, resembles the Parian, but is somewhat denser and finer grained, with occasional greenish zones, produced by greenish talc, whence it is called by the Italians Cipolino statuario. The Parthenon, Propyleum, the Hippodrome, and other principal monuments of Athens, were of Pentelic marble; of which fine specimens may be seen among the Elgin collection, in the British Museum. Marmo Greco, or Greek white marble, is of a very lively snow white colour, rather harder than the preceding, and susceptible of a very fine polish. It was obtained from several islands of the Archipelago, as Scio, Samos, Lesbos, &c. Translucent white marble, Marmo statuario of the Italians, is very much like the Parian, only not so opaque. Columns and altars of this marble exist in Venice, and several towns of Lombardy; but the quarries are quite unknown. Flexible white marble, of which five or six tables are preserved in the house of Prince Borghese, at Rome. The White marble of Luni, on the coast of Tuscany, was preferred by the Greek sculptors to both the Parian and Pentelic. White marble of Carrara, between Specia and Lucca, is of a fine white colour, but often traversed by gray veins, so that it is difficult to procure moderately large pieces free from them. It is not so apt to turn yellow as the Parian marble. This quarry was worked by the ancients, having been opened in the time of Julius CÆsar. Many antique statues remain of this marble. Its two principal quarries at the present day are those of Pianello and Polvazzo. In the centre of its blocks very limpid rock-crystals are sometimes found, which are called Carrara diamonds. As the finest qualities are becoming excessively rare, it has risen in price to about 3 guineas the cubic foot. The White marble of Mount Hymettus, in Greece, was not of a very pure white, but inclined a little to gray. The statue of Meleager, in the French Museum, is of this marble. Black antique marble, the Nero antico of the Italians. This is more intensely black than any of our modern marbles; it is extremely scarce, occurring only in sculptured pieces. The red antique marble, Egyptum of the ancients, and Rosso antico of the Italians, is a beautiful marble of a deep blood-red colour, interspersed with white veins and with very minute white dots, as if strewed over with grains of sand. There is in the Grimani palace at Venice, a colossal statue of Marcus Agrippa in rosso antico, which was formerly preserved in the Pantheon at Rome. Green antique marble, verde antico, is a kind of breccia, whose paste is a mixture of talc and limestone, while the dark green fragments consist of serpentine. Very beautiful specimens of it are preserved at Parma. The best quality has a grass-green paste, with black spots of noble serpentine, but is never mingled with red spots. Red spotted green antique marble, has a dark green ground marked with small red and black spots, with fragments of entrochi changed into white marble. It is known only in small tablets. Leek marble; a rare variety of that colour, Modern marbles.—1. British. Black marble is found at Ashford, Matlock, and Monsaldale in Derbyshire; black and white in the north part of Devonshire; the variegated marbles of Devonshire are generally reddish, brownish, and grayish, variously veined with white and yellow, or the colours are often intimately blended; the marbles from Torbay and Babbacombe, display a great variety in the mixture of their colours; the Plymouth marble is either ash-coloured with black veins, or blackish-gray and white, shaded with black veins; the cliffs near Marychurch exhibit marble quarries not only of great extent, but of superior beauty to any other in Devonshire, being either of a dove-coloured ground with reddish-purple and yellow veins, or of a black ground mottled with purplish globules. The green marble of Anglesea is not unlike the verde antico; its colours being greenish-black, leek-green, and sometimes dull purplish, irregularly blended with white. The white part is limestone, the green shades proceed from serpentine and asbestos. There are several fine varieties of marble in Derbyshire; the mottled-gray in the neighbourhood of Moneyash, the light gray being rendered extremely beautiful by the number of purple veins which spread upon its polished surface in elegant irregular branches; but its chief ornament is the multitude of entrochi, with which this transition limestone-marble abounds. Much of the transition and carboniferous limestone of Wales and Westmoreland is capable of being worked up into agreeable dark marbles. In Scotland, a particularly fine variety of white marble is found in immense beds, at Assynt in Sutherlandshire. A beautiful ash-gray marble of a very uniform grain, and susceptible of a fine polish, occurs on the north side of the ferry of Ballachulish in Invernesshire. One of the most beautiful varieties is that from the hill of Belephetrich in Tiree, one of the Hebrides. Its colours are pale blood-red, light flesh-red, and reddish-white, with dark green particles of hornblende, or rather sahlite, diffused through the general base. The compact marble of Iona is of a fine grain, a dull white colour, somewhat resembling pure compact felspar. It is said by Bournon, to consist of an intimate mixture of tremolite and carbonate of lime, sometimes with yellowish or greenish-yellow spots. The carboniferous limestone of many of the coal basins in the lowlands of Scotland may be worked into a tolerably good marble for chimney-pieces. In Ireland, the Kilkenny marble is the one best known, having a black ground more or less varied with white marks produced by petrifactions. The spar which occupies the place of the shells, sometimes assumes a greenish-yellow colour. An exceedingly fine black marble has also been raised at Crayleath in the county of Down. At Louthlougher, in the county of Tipperary, a fine purple marble is found, which when polished looks very beautiful. The county of Kerry affords several variegated marbles, not unlike the Kilkenny. France possesses a great many marble quarries which have been described by Brard, and of which a copious abstract is given under the article marble,—Rees’ Cyclopedia. The territory of Genoa furnishes several beautiful varieties of marble, the most remarkable of which is the polzevera di Genoa, called in French the vert d’Egypte and vert de mer. It is a mixture of granular limestone with a talcose and serpentine substance disposed in veins; and it is sometimes mixed with a reddish body. This marble was formerly much employed in Italy, France, and England, for chimney-pieces, but its sombre appearance has put it out of fashion. Corsica possesses a good statuary marble of a fine close grain, and pure milky whiteness, quarried at Ornofrio; it will bear comparison with that of Carrara; also a gray marble (bardiglio), a cipolin, and some other varieties. The island of Elba has immense quarries of a white marble with blackish-green veins. Among the innumerable varieties of Italian marbles, the following deserve especial notice. The rovigio, a white marble found at Padua; the white marble of St. Julien, at Pisa, of which the cathedral and celebrated slanting tower are built; the Biancone marble, white with a tinge of gray, quarried at Magurega for altars and tombs. Near Mergozza the white saline marble with gray veins is found, with which the cathedral of Milan is built. The black marble of Bergamo is called paragone, from its black colour, like touchstone; it has a pure intense tint, and is susceptible of a fine polish. The pure black marble of Como is also much esteemed. The polveroso of Pistoya, is a black marble sprinkled with dots; and the beautiful white marble with black spots, from the Lago Maggiore, has been employed for decorating the interior of many churches in the Milanese. The Margorre marble found in several parts of the Milanese, is bluish veined with brown, and composes part of the dome of the cathedral of Milan. The green marble of Florence owes its colour to a copious admixture of steatite. Another green marble, called verde di Prado, occurs in Tuscany, near the little town of Prado. It is marked with spots of a deeper green than the rest, passing even into blackish-blue. The beautiful Sienna marble, or brocatello di Siena, has a yellow colour like the yolk of an egg, which is disposed in large irregular spots, surrounded with veins of bluish-red, passing sometimes into purple. At Montarenti, two leagues from Sienna, another yellow marble is met with, which is traversed by black and purplish-black veins. The Brema marble is yellow with white spots. The mandelato of the Italians is a light red marble with yellowish-white spots, found at Luggezzana, in the Veronese. The red marble of Verona is of a red rather inclining to yellow or hyacinth; a second variety of a dark red, composes the vast amphitheatre of Verona. Another marble is found near Verona, with large white spots in a reddish and greenish paste. Very fine columns have been made of it. The occhio di pavone is an Italian shell marble, in which the shells form large orbicular spots, red, white, and bluish. A madreporic marble known under the name of pietra stellaria, much employed in Italy, is entirely composed of star madrepores, converted into a gray and white substance, and is susceptible of an excellent polish. The village of Bretonico, in the Veronese, furnishes a splendid breccia marble, composed of yellow, steel-gray, and rose-coloured spots. That of Bergamo consists of black and gray fragments in a greenish cement. Florence marble, called also ruin and landscape marble, is an indurated calcareous marl. Sicily abounds in marbles, the most valuable of which is that called by the English stone-cutters, Sicilian jasper; it is red with large stripes like ribands, white, red, and sometimes green, which run zigzag with pretty acute angles. Among the Genoese marbles we may notice the highly esteemed variety called portor, on account of the brilliant yellow veins in a deep black ground. The most beautiful kind comes from Porto-Venese, and Louis XIV. caused a great deal of it to be worked up for the decoration of Versailles. It costs now two pounds per cubic foot. Of cutting and polishing marble.—The marble saw is a thin plate of soft iron, continually supplied during its sawing motion, with water and the sharpest sand. The sawing of moderate pieces is performed by hand, but that of large slabs is most economically done by a proper mill. The first substance used in the polishing process is the sharpest sand, which must be worked with till the surface becomes perfectly flat. Then a second, and even a third sand of increasing fineness is to be applied. The next substance is emery of progressive degrees of fineness, after which tripoli is employed; and the last polish is given with tin-putty. The body with which the sand is rubbed upon the marble, is usually a plate of iron; but for the subsequent process, a plate of lead is used with fine sand and emery. The polishing rubbers are coarse linen cloths, or bagging, wedged tight into an iron planing tool. In every step of the operation, a constant trickling supply of water is required. Visiters of Derby may have an opportunity of inspecting Brown’s extensive machinery for cutting marble into many ornamental forms, which has been well described in Rees’ Cyclopedia. Sir James Jelf patented, in 1822, a combination of machinery for cutting any description of parallel mouldings upon marble slabs, for ornamental purposes; in which, tools, supplied with sand and water, are made to traverse to and fro. Mr. Tullock obtained a patent, in 1824, for improvements in machinery for sawing and grooving marble; the power being applied by means of toothed wheels bearing cranks, which gave the see-saw motion to the cutting iron plates. In November, 1829, Mr. Gibbs secured, by patent, an invention for working ornamental devices in marble, by means of a travelling drill, guided by a mould of wood, &c., in counter relief; and in April, 1833, Mr. G. W. Wilds obtained a patent for machinery, which consists of a series of circular cutters, for separating slabs from a block of marble; the block being advanced slowly to meet the cutters, by the progressive The physical properties of the margaric and stearic acids are very similar; the chief difference is that the former is more fusible, melting at 140° F. The readiest mode of obtaining pure margaric acid, is to dissolve olive oil soap in water, to pour into the solution, a solution of neutral acetate of lead, to wash and dry the precipitate, and then to remove its oleate of lead by ether, which does not affect its margarate of lead. The residuum being decomposed by boiling hot muriatic acid, affords margaric acid. When heated in a retort this acid boils. It is insoluble in water, very soluble in alcohol and ether; it reddens litmus paper, and decomposes with the aid of heat, the carbonates of soda and potash. When first dug up, it is soft, greasy, and lathers like soap; and is on that account used by the Tartars in washing their linen. The well-known Turkey tobacco-pipes are made from it, by a process analogous to that for making pottery ware. The bowls of the pipes, when imported into Germany, are prepared for sale by soaking them first in tallow, then in wax, and finally by polishing them with shave-grass. Mercury combines with great readiness with certain metals, as gold, silver, zinc, tin, and bismuth, forming, in certain proportions, fluid solutions of these metals. Such mercurial alloys are called amalgams. This property is extensively employed in many arts; as in extracting gold and silver from their ores; in gilding, plating, making looking-glasses, &c. Humboldt estimates at 16,000 quintals, of 100 lbs. each, the quantity of mercury annually employed at his visit to America, in the treatment of the mines of New Spain; three-fourths of which came from European mines. The mercurial ores may be divided into four species:— 1. Native quicksilver.—It occurs in most of the mines of the other mercurial ores, in the form of small drops attached to the rocks, or lodged in the crevices of other ores. 2. Argental mercury, or native silver amalgam.—It has a silver-white colour, and is more or less soft, according to the proportion which the mercury bears to the silver. Its density is sometimes so high as 14. A moderate heat dissipates the mercury, and leaves the silver. Klaproth states its constituents at silver 36, and mercury 64, in 100; but Cordier makes them to be, 271/2 silver, and 721/2 mercury. It occurs crystallized in a variety of forms. It has been found in the territory of Deux-Ponts, at Rozenau and Niderstana, in Hungary, in a canton of Tyrol, at Sahlberg in Sweden, at Kolyvan in Siberia, and at AllÉmont in Dauphiny; in small quantity at Almaden in Spain, and at Idria in Carniola. By the chemical union of the mercury with the silver, the amalgam, which should by calculation have a spec. grav. of only 12·5, acquires that of 14·11, according to M. Cordier. 3. Sulphuret of mercury, commonly called Cinnabar, is a red mineral of various shades; burning at the blowpipe with a blue flame, volatilizing entirely with the smell of burning sulphur, and giving a quicksilver coating to a plate of copper held in the fumes. Even the powder of cinnabar rubbed on copper whitens it. Its density varies from 6·9 to 10·2. It becomes negatively electrical by friction. Analysed by Klaproth, it was found to consist of mercury 84·5, sulphur 14·75. Its composition, viewed as a bisulphuret of mercury, is, mercury 86·2, sulphur 13·8. The finest crystals of sulphuret of mercury come from China, and Almaden in Spain. These contain, according to Klaproth, 85 per cent. of mercury. A bituminous sulphuret of mercury appears to be the base of the great exploration of Idria; it is of a dark liver-red hue; and of a slaty texture, with straight or twisted plates. It exists in large masses in the bituminous schists of Idria. M. Beurard mentions also the locality of Munster-Appel, in the duchy of Deux-Ponts, where the ore includes impressions of fishes, curiously spotted with cinnabar. The compact variety of the Idria ore seems very complex in composition, according to the following analysis of Klaproth:—Mercury, 81·8; sulphur, 13·75; carbon, 2·3; silica, 0·65; alumina, 0·55; oxide of iron, 0·20; copper, 0·02; water, 0·73; in 100 parts. M. Beurard mentions another variety from the Palatinate, which yields a large quantity of bitumen by distillation; and it was present in all the specimens of these ores analyzed by me for the German Mines Company. At Idria and Almaden the sulphurets are extremely rich in mercury. 4. Muriated mercury, or the Chloride of mercury, commonly called Horn mercury. This ore occurs in very small crystals of a pearl-gray or greenish-gray colour, or in small nipples which stud, like crystals, the cavities, fissures, or geodes among the ferruginous gangues of the other ores of mercury. It is brittle, and entirely volatile at the blowpipe, characters which distinguish it from horn silver. The geological position of the mercurial ores, in all parts of the world, is in the strata which commence the series of secondary formations. Sometimes they are found in the red sandstone above the coal, as at Menildot, in the old dutchy of Deux-Ponts, at Durasno in Mexico, at CuenÇa in New Granada, at Cerros de Gauzan and Upar in Peru; in the subordinate porphyries, as at Deux-Ponts, San Juan de la Chica in Peru, and at Cerro-del-Fraile, near the town of San-Felipe, they occur also among the strata below, or subordinate to the calcareous formation, called zechstein, in Germany, or They are even sometimes accompanied with the remains of organic bodies, such as casts of fishes, fossil shells, silicified wood, and true coal. The last fact has been observed at Potzberg, in the works of Drey-Koenigszug, by M. Brongniart. These sandstones, bituminous schists, and indurated clays, contain mercury both in the state of sulphuret and in the native form. They are more or less penetrated with the ore, forming sometimes numerous beds of very great thickness; while, in the more antient or the primitive formations, these ores exist only in very small quantity associated with tin. Mercury is, generally speaking, a metal sparingly distributed in nature, and its mines are very rare. The great exploitations of Idria in Friuli, in the county of Goritz, were discovered in 1497, and the principal ore mined there is the bituminous sulphuret. The workings of this mine have been pushed to the depth of 280 yards. The product in quicksilver might easily amount annually to 6000 metric quintals = 600 tons British; but, in order to uphold the price of the metal, the Austrian government has restricted the production to 150 tons. The memorable fire of 1803 was most disastrous to these mines. It was extinguished only by drowning all the underground workings. The sublimed mercury in this catastrophe occasioned diseases and nervous tremblings to more than 900 persons in the neighbourhood. Pliny has recorded two interesting facts: 1. that the Greeks imported red cinnabar from Almaden 700 years before the Christian era; and 2. that Rome, in his time, annually received 700,000 pounds from the same mines. Since 1827, they have produced 22,000 cwts. of mercury every year, with a corps of 700 miners and 200 smelters; and, indeed, the veins are so extremely rich, that though they have been worked pretty constantly during so many centuries, the mines have hardly reached the depth of 330 yards, or something less than 1000 feet. The lode actually under exploration is from 14 to 16 yards thick, and it becomes thicker still at the crossing of the veins. The totality of the ore is extracted. It yields in their smelting works only 10 per cent. upon an average, but there is no doubt, from the analysis of the ores, that nearly one half of the quicksilver is lost, and dispersed in the air, to the great injury of the workmen’s health, in consequence of the barbarous apparatus of aludels employed in its sublimation; an apparatus which has remained without any material change for the better since the days of the Moorish dominion in Spain. M. Le Play, the eminent Ingenieur des Mines, who published, in a recent volume of the Annales des Mines, his ItinÉraire to Almaden, says, that the mercurial contents of the ores are notablement plus elevÉes than the product. These veins extend all the way from the town of Chillon to Almadenejos. Upon the borders of the streamlet Balde Azogues, a black slate is also mined which is abundantly impregnated with metallic mercury. The ores are treated in 13 double furnaces, which I shall presently describe. “Le mercure,” says M. Le Play, “a sur la santÉ des ouvriers la plus funeste influence, et l’on ne peut se dÉfendre d’un sentiment pÉnible en voyant l’empressement avec lequel des jeunes gens, pleins de force et de santÉ, se disputent la faveur d’aller chercher dans les mines, des maladies cruelles, et souvent une mort prÉmaturÉe. La population des mineurs d’Almaden mÉritent le plus haut interÊt.” These victims of a deplorable mismanagement are described as being a laborious, simple-minded, virtuous race of beings, who are thus condemned to breathe an atmosphere impregnated far and near with the fumes of a volatile poison, which the lessons of science, as I shall presently demonstrate, might readily repress, with the effect of not only protecting the health of the population, but of vastly augmenting the revenues of the state. These celebrated mines, near to which lie those of Las Cuebas and of Almadenejos, were known to the Romans. After having been the property of the religious knights of Calatrava, who had assisted in expelling the Moors, they were farmed off to the celebrated Fugger merchants of Augsbourg; and afterwards explored on account of the government, from the date of 1645 till the present time. Their produce was, till very lately, entirely appropriated to the treatment of the gold and silver ores of the new world. The mines of the Palatinate, situated on the left bank of the Rhine, though they do not approach in richness and importance to those of Idria and Almaden, merit, however, all the attention of the government that farms them out. They are numerous, and varied in geological position. Those of Drey-Koenigszug, at Potzberg, near Kussel, deserve particular notice. The workings have reached a depth of more than 220 yards; the ore being a sandstone strongly impregnated with sulphuret of mercury. The produce of these mines is estimated at about 30 tons per annum. There are also in Hungary, Bohemia, and several other parts of Germany, some inconsiderable exploitations of mercury, the total produce of which is valued at about 30 or 40 tons on an average of several years. The mines of Guancavelica, in Peru, are the more interesting, as their products are directly employed in treating the ores of gold and silver, which abound in that portion of America. These quicksilver mines, explored since 1570, produced, up to 1800, 53,700 tons of that metal; but the actual produce of the explorations of these countries was, according to Helms, about the beginning of this century, from 170 to 180 tons per annum. In 1782 recourse was had by the South American miners to the mercury extracted in the province of Yun-nan, in China. The metallurgic treatment of the quicksilver ores is tolerably simple. In general, when the sulphuret of mercury, the most common ore, has been pulverized, and sometimes washed, it is introduced into retorts of cast iron, sheet iron, or even stoneware, in mixture with an equal weight of quicklime. These retorts are arranged in various ways. Prior to the 17th century, the method called per descensum was the only one in use for distilling mercury; and it was effected by means of two earthen pots adjusted over each other. The upper pot, filled with ore, and closed at the top, was covered over with burning fuel; and the mercurial vapours expelled by the heat, passed down through small holes in the bottom of the pot, to be condensed in another vessel placed below. However convenient this apparatus might be, on account of the facility of transporting it, wherever the ore was found, its inefficiency and the losses it occasioned were eventually recognized. Hence, before 1635, some smelting works of the Palatinate had given up the method per descensum, which was, however, still retained in Idria; and they substituted for it the furnaces called galleries. At first earthenware retorts were employed in these furnaces; but they were soon succeeded by iron retorts. In the Palatinate this mode of operating is still in use. At Idria, in the year 1750, a great distillatory apparatus was established for the treatment of the mercurial ores, in imitation of those which previously existed at Almaden, in Spain, and called aludel-furnaces. But, since 1794, these aludels have been suppressed, and new distillatory apparatus have been constructed at Idria, remarkable only for their magnitude; exceeding, in this respect, every other metallurgic erection. There exist, therefore, three kinds of apparatus for the distillation of mercury: 1. the furnace called a gallery; 2. the furnace with aludels; and 3. the large apparatus of Idria. I shall describe each of these briefly, in succession. 1. Furnace called Gallery of the Palatinate.—The construction of this furnace is disposed so as to contain four ranges, a a', b b', of large retorts, styled cucurbits, of cast iron, in which the ore of mercury is subjected to distillation. This arrangement is shewn in fig. 656., which presents a vertical section in the line a b of the ground plan, fig. 657. In the ground plan, the roof e e' of the furnace (fig. 656.) is supposed to be lifted off, in order to shew the disposition of the four ranges of cucurbits upon the grate c f, figs. 656, 657., which receives the pit-coal employed as fuel. Under this grate extends an ash-pit d. Fig. 658., which exhibits an elevation of the furnace, points out this ash-pit, as well as one of the two doors c, by which the fuel is thrown upon the grate c f. Openings e e, (fig. 656.) are left over the top arch of the furnace, whereby the draught of air may receive a suitable direction. The grate of the fire-place extends over the whole length of the furnace, fig. 657., from the door c to the door f, situated at the opposite extremity. The furnace called gallery includes commonly 30 cucurbits, and in some establishments even 52. Into each are introduced from 56 to 70 pounds of ore, and 15 to 18 pounds of quicklime, a mixture which fills no more than two-thirds of the cucurbit; to the neck a stoneware receiver is adapted, containing water to half its height. The fire, at first moderate, is eventually pushed till the cucurbits are red hot. The operation being concluded, the contents of the receivers are poured out into a wooden bowl placed upon a plank above a bucket; the quicksilver falls to the bottom Aludel furnaces of Almaden.—Figs. 659. and 660. represent the great furnaces with aludels in use at Almaden, and anciently in Idria; for between the two establishments there was in fact little difference before the year 1794. Figs. 659. and 662. present two vertical sections; figs. 660. and 661. are two plans of two similar furnaces, conjoined in one body of brickwork. In the four figures the following objects are to be remarked; a door a, by which the wood is introduced into the fire-place b. This is perforated with holes for the passage of air; the ash-pit c, is seen beneath. An upper chamber d, contains the mercurial ores distributed upon open arches, which form the perforated sole of this chamber. Immediately over these arches, there are piled up in a dome form, large blocks of a limestone, very poor in quicksilver ore; above these are laid blocks of a smaller size, then ores of rather inferior quality, and stamped ores mixed with richer minerals. Lastly, the whole is covered up with soft bricks, formed of clay kneaded with schlich, and with small pieces of sulphuret of mercury. Six ranges of aludels or stoneware tubes, f f, of a pear shape, luted together with clay, are mounted in front of each of the two furnaces, on a double sloping terrace, having in its lowest middle line two gutters t v, a little inclined towards the intermediate wall m. In each range the aludel placed at the line t m v of fig. 660., that is to say at the lowest point, g, figs. 659. 662., is pierced with a hole. Thereby the mercury which had been volatilized in d, if it be already condensed by the cooling in the series of aludels f g, may pass into the corresponding gutter, next into the hole m, fig. 660., and after that into the wooden pipes h h', fig. 659., which conduct it across the masonry of the terrace into cisterns filled with water; see q, fig. 661., which is the plan of fig. 662. The portion of mercury not condensed in the range of aludels, f g, which is the most Details of the aludel apparatus: 25 are set in each of the 12 ranges, seen in fig. 661. constituting 300 pear-shaped stoneware vessels, open at both ends, being merely thrust into one another, and luted with loam. What a multitude of joints, of which a great many must be continually giving way by the shrinkage of the luting, whereby the mercurial fumes will escape with great loss of product, to poison the air! a, is the door of the fire-place; c, the perforated arches upon which the ore is piled in the chamber e, through the door d, and an orifice at top; the latter being closed during the distillation; f f are vents for conducting the mercurial vapours into two chambers i, separated by a triangular body of masonry m n; h is the smoke chimney of the fire-place; o o, are the ranges of aludels, in connection with the chamber i, which are laid slantingly towards the gutter q, upon the double inclined plane terrace, and terminate in the chamber h q; this being surmounted by two chimneys t. The mercury is collected in these aludels and in the basins at q and p, fig. 661. r is a thin stone partition set up between the two principal walls of each of the furnaces. v is the stair of the aludel terrace, leading to the platform which surmounts the furnace; z is a gutter for conducting away the rains which may fall upon the buildings. Great apparatus of Idria.—Before entering into details of this laboratory, it will not be useless to recapitulate the metallurgic classification of the ores treated in it. 1. The ores in large blocks, fragments, or shivers, whose size varies from a cubic foot to that of a nut. 2. The smaller ores, from the size of a nut to that of grains of dust. The first class of large ores comprises three subdivisions, namely; a, blocks of metalliferous rocks, which is the most abundant and the poorest species of ore, affording only one per cent. of mercury; b, the massive sulphuret of mercury, the richest and rarest ore, yielding 80 per cent. when it is picked; c, the fragments or splinters proceeding from the breaking and sorting, and which vary in value, from 1 to 40 per cent. The second class of small ores comprises: d, the fragments or shivers extracted from the mine in the state of little pieces, affording from 10 to 12 per cent.; e, the kernels of ore, separated on the sieve, yielding 32 per cent.; f, the sands and paste called schlich, obtained in the treatment of the poorest ores, by means of the stamps and washing tables; 100 parts of this schlich give at least 8 of quicksilver. The general aspect of the apparatus is indicated by figs. 663, 664. and 665. Fig. 665. represents the exterior, but only one half, which is enough, as it resembles exactly the other, which is not shown. In these three figures the following objects may be distinguished; figs. 663, 664., a, door of the fire-place; b, the furnace in which beech-wood is burned mixed with a little fir-wood; c, door of the ash-pit, extended beneath; d, a space in which the ores are deposited upon the seven arches, 1. to 7., as indicated in figs. 663. and 666.; e e, brick tunnels, by which the smoke of the fuel and the vapours of mercury pass, on the one side, into successive chambers f k. f g h i j k l are passages which permit the circulation of the vapours from the furnace a b c d, to the chimneys l l. Figs. 663. and 664. exhibit clearly the distribution of these m m', fig. 664., are basins of reception, distributed before the doors of each of the chambers f k f' k'. The condensed mercury which flows out of the chambers is conveyed thither. n n' is a trench into which the mercury, after being lifted into the basins m, is poured, so that it may run towards a common chamber o, in the sloping direction indicated by the arrows. o leads to the chamber where the mercury is received into a porphyry trough; out of which it is laded and packed up in portions of 50 or 100 lbs. in sheep-skins prepared with alum. p p', fig. 663., are vaulted arches, through which a circulation may go on round the furnace a b c d, on the ground level, q q' are the vaults of the upper stories. r r', fig. 665., vaults which permit access to the tunnels e' e'', fig. 663. s s' and t t', fig. 665., are the doors of the chambers, f k and f' k'. These openings are shut during the distillation by wooden doors faced with iron, and luted with a mortar of clay and lime. u u' is the door of the vaults 1. to 7. of the furnace represented in fig. 663. These openings are hermetically shut, like the preceding. v v', fig. 663., are superior openings of the chambers, closed during the operation by luted plugs; they are opened afterwards to facilitate the cooling of the apparatus, and to collect the mercurial soot. x y z, fig. 666., are floors which correspond to the doors u u' of the vaults 1. to 7., fig. 665. These floors are reached by stairs set up in the different parts of the building, which contains the whole apparatus. On the lower arches the largest blocks of metalliferous rock are laid; over these the less bulky fragments are arranged, which are covered with the shivers and pieces of less dimension. On the middle vaults, the small ore is placed, distributed into cylindrical pipkins of earthenware, of 10 inches diameter and 5 inches depth. The upper vaults receive likewise pipkins filled with the sands and pastes called schlich. In 3 hours, by the labour of 40 men, the two double sets of apparatus are charged, and all the apertures are closed. A quick fire of beech-wood is then kindled; and when the whole mass has become sufficiently heated, the sulphuret of mercury begins to vapourize; coming into contact with the portion of oxygen which had not been carbonated, by combustion, its sulphur burns into sulphurous acid, while the mercury becomes free, passes with the other vapours into the chambers for condensing it, and precipitates in the liquid form at a greater or less distance from the fire-place. The walls of the chambers and the floors, with which their lower portion is covered, are soon coated over with a black mercurial soot, which, being treated anew, furnishes 50 per cent. of mercury. The distillation lasts from 10 to 12 hours; during which time the whole furnace is kept at a cherry-red heat. A complete charge for the two double apparatus, consists of from 1000 to 1300 quintals of ore, which produce from 80 to 90 quintals of running mercury. The furnace takes from 5 or 6 days to cool, according to the state of the weather; and if to that period be added the time requisite for withdrawing the residuums, and attending to such repairs as the furnace may need, it is obvious that only one distillation can be performed in the course of a week. In the works of Idria, in 1812, 56,686 quintals and a half of quicksilver ores were distilled, after undergoing a very careful mechanical preparation. They afforded 4832 quintals of running mercury; a quantity corresponding to about 81/2 per cent. of the ore. These smelting works are about 180 feet long and 30 feet high. Upon the preceding three systems of smelting mercurial ores, I shall now make some observations. It has been long well known, that quicksilver may be most readily extracted from cinnabar, by heating it in contact with quicklime. The sulphur of the cinnabar combines, The annual production of the Bavarian Rhine provinces has been estimated at from 400 to 550 quintals; that of Almaden, in the year 1827, was 22,000 quintals; and of Idria, at present, is not more than 1500 quintals. All the plans hitherto prescribed for distilling the ore along with quicklime, are remarkably rude. In that practised at Landsberg by Obermoschel, there is a great waste of labour, in charging the numerous small cucurbits; there is a great waste of fuel in the mode of heating them; a great waste of mercury by the imperfect luting of the retorts to the receivers, as well as the imperfect condensation of the mercurial vapours; and probably a considerable loss by pilfering. The modes practised at Almaden and Idria are, in the greatest degree, barbarous; the ores being heated upon open arches, and the vapours attempted to be condensed by enclosing them within brick or stone and mortar walls, which can never be rendered either sufficiently tight or cool. To obviate all these inconveniences and sources of loss, the proper chemical arrangements suited to the present improved state of the arts ought to be adopted, by which labour, fuel, and mercury, might all be economized to the utmost extent. The only apparatus fit to be employed is a series of cast-iron cylinder retorts, somewhat like those employed in the coal gas works, but with peculiarities suited to the condensation of the mercurial vapours. Into each of these retorts, supposed to be at least one foot square in area, and 7 feet long, 6 or 7 cwt. of a mixture of the ground ore with the quicklime, may be easily introduced, from a measured heap, by means of a shovel. The specific gravity of the cinnabar being more than 6 times that of water, a cubic foot of it will weigh more than 31/2 cwt.; but supposing the mixture of it with quicklime (when the ore does not contain the calcareous matter itself) to be only thrice the density of water, then four cubic feet might be put into each of the above retorts, and still leave 11/2 cubic feet of empty space for the expansion of volume which may take place in the decomposition. The ore should certainly be ground to a moderately fine powder, by stamps, iron cylinders, or an edge wheel, so that when mixed with quicklime, the cinnabar may be brought into intimate contact with its decomposer, otherwise much of it will be dissipated unproductively in fumes, for it is extremely volatile. Figs. 667, 668, 669. represent a cheap and powerful apparatus which I contrived at the request of the German Mines Company of London, and which is now mounted at Landsberg, near Obermoschel, in the Bavarian Rhein-Kreis. Fig. 667. is a section parallel to the front elevation of three arched benches of retorts, of the size above specified. Each bench contains 3 retorts, of the form represented by a a a. I, is the single fire-place or furnace, capable of giving adequate ignition by coal or wood, to the three retorts. The retorts were built up in an excellent manner, by an English mason perfectly acquainted with the best modes of erecting coal-gas retorts, who was sent over on purpose. The path of the flame and smoke is precisely similar to that represented in fig. 483, page 549, whereby the uppermost retort is immersed in a bath of uniformly ignited air, while the currents reverberated from the top, play round the two undermost retorts, in their way to the vent-flues beneath In the section, fig. 668., a is the body of the retort; its mouth at the right hand end is shut, as usual, by a luted iron lid, secured with a cross-bar and screw-bolts; its other end is prolonged by a sloping pipe of cast iron, 4 inches in diameter, furnished with a nozzle hole at L, closed with a screw plug. Through this hole a wire rammer may be introduced, to ascertain that the tube is pervious, and to cleanse it from the mercurial soot, when thought necessary. c, is a cross section of the main condenser, shown in a longitudinal section at C C, fig. 669. This pipe is 18 inches in diameter, and about 20 feet long. At a a, &c., the back ends of the retorts are seen, with the slanting tubes b b, &c., descending through orifices in the upper surface of the condenser pipe, and dipping their ends just below the water-line h i. g, is the cap of a water valve, which removes all risk from sudden expansion or condensation. The condenser is placed within a rectangular trough, made either of wood or stone, through which a sufficient stream of water passes to keep it perfectly cool, and repress every trace of mercurial vapour, and it is laid with a slight inclination from i to h, so that the condensed quicksilver may spontaneously flow along its bottom, and pass through the vertical tube D into the locked up iron chest, or magazine e. This tube D is from the beginning closed at bottom, by immersion in a shallow iron cup, always filled with mercury. k is a graduated gauge rod, to indicate the progressive accumulation of quicksilver in the chest, without being under the necessity of unlocking it. This air-tight apparatus was erected about a year ago, and has been found to act perfectly well; I regret, however, that my professional engagements at home have not hitherto permitted me to conduct its operations personally for some days. The average samples of cinnabar ore from Obermoschel are ten times poorer than those of Almaden. Were such an apparatus as the above, with some slight modifications which have lately occurred to me, mounted for the Spanish mines, I am confident that their produce in quicksilver might be nearly doubled, with a vast economy of fuel, labour, and human life. The whole cost of the 9 large retorts, with their condensing apparatus, iron magazine, &c., was very little more than two hundred pounds! As the retorts are kept in a state of nearly uniform ignition, like those of the gas works, neither they, nor the furnaces are liable to be injured in their joints by the alternate contractions and expansions, which they would inevitably suffer if allowed to cool; and being always ready heated to the proper pitch for decomposing the mercurial ores, they are capable of working off a charge, under skilful management, in the course of 3 hours. Thus, in 24 hours, with a relay of labourers, 8 charges of at least 5 cwts. of ore each, might be smelted = 2 tons, with 3 retorts, and 6 tons with 9 retorts; with a daily product from the rich ores of Almaden, or even Idria, of from 12 cwts. to 20 cwts. Instead of 3 benches of 3 retorts each, I would recommend 15 benches, containing 45 retorts, to be erected for either the Almaden or Idria mines; which, while they would smelt all their ores, could be got for a sum not much exceeding 1000l., an outlay which they would reimburse within a month or two. Quicksilver is a substance of paramount value to science. Its great density and its regular rate of expansion and contraction by increase and diminution of temperature, This metal alloyed with tin-foil forms the reflecting surface of looking glasses, and by its ready solution of gold or silver, and subsequent dissipation by a moderate heat, it becomes the great instrument of the arts of gilding and silvering copper and brass. The same property makes it so available in extracting these precious metals from their ores. The anatomist applies it elegantly, to distend and display the minuter vessels of the lymphatic system, and secretory systems, by injecting it with a syringe through all their convolutions. It is the basis of many very powerful medicines, at present probably too indiscriminately used, to the great detriment of English society; for it is far more sparingly prescribed by practitioners upon the continent of Europe, not otherwise superior in skill or science to those of Great Britain. The nitrate of mercury is employed for the secrÉtage of rabbit and hare-skins, that is, for communicating to the fur of these and other quadrupeds the faculty of felting, which they do not naturally possess. With this view the solution of that salt is applied to them lightly in one direction with a sponge. A compound amalgam of zinc and tin is probably the best exciter which can be applied to the cushions of electrical machines. Mercury imported for home consumption in 1836, 286,808 lbs.; in 1837, 314,036 lbs. The only mercurial compounds which are extensively used in the arts, are fictitious cinnabar or Vermillion, and corrosive sublimate. In the valuable work upon the dry rot, published by Mr. Knowles, secretary of the committee of inspectors of the navy, in 1821, corrosive sublimate is enumerated among the chemical substances which had been prescribed for preventing the dry rot in timber; and it is well known that Sir H. Davy had, several years before that date, used and recommended to the Admiralty and Navy Board, corrosive sublimate as an anti-dry rot application. It has been since extensively employed by a joint-stock company for the same purpose, under the title of Kyan’s patent. The following more economical process is that adopted at the Apothecaries’ Hall, London. 140 pounds of concentrated sulphuric acid are boiled in a cast iron pot upon 100 pounds of mercury, till a dry persulphate is obtained. Of this salt, 124 pounds are triturated with 81 pounds of mercury, till the globules disappear, and till a protosulphate be formed. This is to be intimately mixed with 68 pounds of sea-salt, and the mixture, being put into a large stone-ware cucurbit, is to be submitted to a subliming heat. See Calomel. From 190 to 200 pounds of calomel rise in a crystalline cake, as in the former process, into the capital; while sulphate of soda remains at the bottom of the alembic. The calomel must be ground to an impalpable powder, and elutriated. The vapours, instead of being condensed into a cake within the top of the globe or in a capital, may be allowed to diffuse themselves into a close vessel, containing water in a state of ebullition, whereby the calomel is obtained at once in the form of a washed impalpable powder. Calomel is tasteless and insoluble in water. Its specific gravity is 7·176. Notwithstanding the striking analogy which exists between common chemical and metallurgic operations, since both are employed to insulate certain bodies from others, there are essential differences which should be carefully noted. In the first place, the quantity of materials being always very great in metallurgy, requires corresponding adaptations of apparatus, and often produces peculiar phenomena; in the second place, the agents to be employed for treating great masses, must be selected with a view to economy, as well as to chemical action. In analytical chemistry, the main object being exactness of result, and purity of product, little attention is bestowed upon the value of the reagents, on account of the small quantity required for any particular process. But in smelting metals upon the great scale, profit being the sole object, cheap materials and easy operations alone are admissible. The metallic ores as presented by nature, are almost always mixed with a considerable number of foreign substances; and could not therefore be advantageously submitted to metallurgic operations, till they are purified and concentrated to a certain degree by various methods. OF THE PREPARATION OF ORES FOR THE SMELTING HOUSE. There are two kinds of preparation; the one termed mechanical, from the means employed, and the results obtained, consists in processes for breaking and grinding the ores, and for washing them so as to separate the vein-stones, gangues, or other mixed earthy matters, in order to insulate or concentrate the metallic parts. Another kind of preparation, called chemical, has for its object to separate, by means of fire, various volatile substances combined in the ores, and which it is requisite to clear away, at least in a certain degree, before trying to extract the metals they may contain. Lastly, an indispensable operation in several circumstances, is to discover, by simple and cheap methods, called assays, the quantity of metal contained in the different species of ores to be treated. This head of our subject, therefore, falls under three subdivisions:— § 1. The mechanical preparation of ores, including picking, stamping, and different modes of washing. § 2. The chemical preparation, consisting especially in the roasting or calcination of the ores. § 3. The assay of ores, comprehending the mechanical part: that is, by washing; the chemical part, or assays by the dry way; and the assays by the moist way. Section 1. Of the mechanical preparation or dressing of ores.—I. The first picking or sorting takes place in the interior, or underground, workings, and consists in separating the fragments of rocks, that apparently contain no metallic matter, from those that contain more or less of it. The external aspect guides this separation; as also the feeling of density in the hand. The substances when turned out to the day, undergo another sorting, with greater or less care, according to the value of the included metal. This operation consists in breaking the lumps of ore with the hammer, into fragments of greater or less size, usually as large as the fist, whereby all the pieces may be picked out and thrown away that contain no metal, and even such as contain too little to be smelted with advantage. There is for the most part, a building erected near the output of the mine, in which the breaking and picking of the ores are performed. In a covered gallery, or under a shed, banks of earth are thrown up, and divided into separate beds, on each of which a thick plate of cast iron is laid. On this plate, elderly workmen, women, and children, break the ores with hand hammers, then pick and sort them piece by piece. The matters so treated, are usually separated into three parts; 1. the rock or sterile gangue, which is thrown away; 2. the ore for the stamping mill, which presents too intimate a mixture of rock and metallic substance to admit of separation by breaking and picking; and 3. the pure ore, or at least the very rich portion, called the sorted mine or the fat ore. On the sorting floors there remains much small rubbish, which might form a fourth subdivision of ore, since it is treated in a peculiar manner, by sifting, as will be presently mentioned. The distribution of fragments more or less rich, in one class or another, is relative to the value of the included metal, taking into account the expenses necessary for its extraction. II. The very simple operations of picking are common to almost all ores; but there are other operations requiring more skill, care, and expense, which are employed in their final state of perfection only upon ores of metals possessing a certain value, as those of lead, silver, &c. We allude to the washing of ores. The most simple and economical washings are those that certain iron ores, particularly the alluvial, are subjected to, as they are found near the surface of the ground agglutinated in great or little pieces. It is often useful to clean these pieces, in order to pick out the earthy lumps, which would be altogether injurious in the furnaces. This crude washing is performed sometimes by men stirring in the midst of a stream of water, with iron rakes or shovels, the lumps of ore placed in large chests, or basins of wood or iron. In other situations, this washing is executed more economically by a machine called a buddle or dolly-tub by our miners. A trough of wood or iron, with a concave bottom, is filled with the ore to be washed. Within the tub or trough, arms or iron handles are moved round about, being attached to the arbor of a hydraulic wheel. The trough is kept always full of water, which as it is renewed carries off the earthy matters, diffused through it by the motion of the machine, and the friction among the pieces of the ore. When the washing is finished, a door in one of the sides of the trough is opened, and the current removes the ore into a more spacious basin, where it is subjected to a kind of picking. It is frequently indeed passed through sieves in different modes. See Lead and Tin, for figures of buddles and dollies. III. Stamping. Before describing the refined methods of washing the more valuable ores of copper, silver, lead, &c., it is proper to point out the means of reducing them into a powder of greater or less fineness, by stamping, so called from the name stamps of the pestles employed for that purpose. Its usefulness is not restricted to preparing the ores; for it is employed in almost every smelting house for pounding clays, charcoal, scoriÆ, &c. A stamping mill or pounding machine, fig. 670., consists of several movable pillars of wood l l l, placed vertically, and supported in this position between frames of carpentry K K K. These pieces are each armed at their under end with a mass of iron m. An arbor or axle a a, moved by water, and turning horizontally, tosses up these wooden pestles, by means of wipers or cams, which lay hold of the shoulders of the pestles at l l l. These are raised in succession, and fall into an oblong trough below m m, scooped out in the ground, having its bottom covered either with plates of iron or hard stones. In this trough, beneath these pestles, the ore to be stamped is allowed to fall from a hopper above, which is kept constantly full. The trough is closed in at the sides by two partitions, and includes three or four pestles; which the French miners call a battery. They are so disposed that their ascent and descent take place at equal intervals of time. Usually a stamping machine is composed of several batteries (two, three, or four), and the arrangement of the wipers on the arbor of the hydraulic wheel is such that there is constantly a like number of pestles lifted at a time; a circumstance important for maintaining the uniform going of the machine. The matters that are not to be exposed to subsequent washing are stamped dry, that is without leading water into the trough; and the same thing is sometimes done with the rich ores, whose lighter parts might otherwise be lost. Most usually, especially for ores of lead, silver, copper, &c., the trough of the stamper is placed in the middle of a current of water, of greater or less force; which, sweeping off the pounded substances, deposits them at a greater or less distance onwards, in the order of the size and richness of the grain; constituting a first washing, as they escape from beneath the pestles. In the dry stamping, the fineness of the powder depends on the weight of the pestles, the height of their fall, and the period of their action upon the ore; but in the stampers exposed to a stream of water, the retention of the matters in the trough is longer or shorter, according to the facility given for their escape. Sometimes these matters flow out of the chest over its edges, and the height of the line they must surmount has an influence on the size of the grain; at other times, the water and the pounded matter The size of the particles of the pounded ore being different, according to the variable hardness of the matters which compose them, suggests the means of classing them, and distributing them nearly in the order of their size and specific gravity, by making the water, as it escapes from the stamping trough, circulate in a system of canals called a labyrinth, where it deposits successively, in proportion as it loses its velocity, the earthy and metallic matters it had floated along. These metalliferous portions, especially when they have a great specific gravity like galena, would be deposited in the first passages, were it not that from their hardness being inferior to that of the gangue, they are reduced to a much finer powder, or into thin plates, which seem to adhere to both the watery and earthy particles; whence they have to be sought for among the finest portions of the pulverised gangue, called slime, schlich, or schlamme. There are several methods of conducting the stamps; in reference to the size of the grains wished to be obtained, and which is previously determined agreeably to the nature of the ore, and of the gangue; its richness, &c. The height of the slit that lets the pounded matters escape, or the diameters of the holes in the grating, their distance, the quantity of water flowing in, its velocity, &c., modify the result of the stamping operation. When it is requisite to obtain powder of an extreme fineness, as for ores that are to be subjected to the process of amalgamation, they are passed under millstones, as in common corn mills; and after grinding, they are bolted so as to form a species of flour; or they are crushed between rolls. See Lead and Tin. Washing of ores. IV. The ores pounded under the stamps are next exposed to very delicate operations, both tedious and costly, which are called the washings. Their purpose is to separate mechanically the earthy matters from the metallic portion, which must therefore have a much higher specific gravity; for otherwise, the washing would be impracticable. The medium employed to diminish the difference of specific gravity, and to move along the lightest matters, is water; which is made to flow with greater or less velocity and abundance over the schlich or pasty mud spread on a table of various inclination. But as this operation always occasions, not only considerable expense, but a certain loss of metal, it is right to calculate what is the degree of richness below which washing is unprofitable; and on the other hand, what is the degree of purification of the schlich at which it is proper to stop, because too much metal would be lost comparatively with the expense of fusing a small additional quantity of gangue. There cannot, indeed, be any fixed rule in this respect, since the elements of these calculations vary for every work. Before describing the different modes of washing, we must treat of the sifting or riddling, whose purpose, like that of the labyrinth succeeding the stamps, is to distribute and to separate the ores (which have not passed through the water stamps) in the order of the coarseness of grain. This operation is practised particularly upon the debris of the mine, and the rubbish produced in breaking the ores. These substances are put into a riddle, or species of round or square sieve, whose bottom is formed of a grating instead of a plate of metal pierced with holes. This riddle is plunged suddenly and repeatedly into a tub or cistern filled with water. This liquid enters through the bottom, raises up the mineral particles, separates them and keeps them suspended for an instant, after which they fall down in nearly the order of their specific gravities, and are thus classed with a certain degree of regularity. The sieve is sometimes dipped by the immediate effort of the washer; sometimes it is suspended to a swing which the workman moves; in order that the riddling may be rightly done, the sieve should receive but a single movement from below upwards; in this case the ore is separated from the gangue, and if there be different specific gravities, there is formed in the sieve as many distinct strata, which the workman can easily take out with a spatula, throwing the upper part away when it is too poor to be re-sifted. This operation by the hand-sieve, is called riddling in the tub, or riddling by deposit. We may observe, that during the sifting, the particles which can pass across the holes of the bottom, fall into the tub and settle down there; whence they are afterwards gathered out, and exposed to washing when they are worth the trouble. Sometimes, as at Poullaouen, the sieves are conical, and held by means of two handles by a workman; and instead of receiving a single movement, as in the preceding method, the sifter himself gives them a variety of dexterous movements in succession. His object is to separate the poor portions of the ore from the richer; in order to subject the former to the stamp mill. Among the siftings and washings which ores are made to undergo, we must notice Fig. 671 enlarged (103 kB) The grilles anglaises are similar to the sleeping tables used at Idria. The system of these en gradins is represented in fig. 671. There are 5 such systems in the works at Idria, for the sorting of the small morsels of quicksilver ore, intended for the stamping mill. These fragments are but moderately rich in metal, and are picked up at random, of various sizes, from that of the fist to a grain of dust. These ores are placed in the chest a, below the level of which 7 grates are distributed, so that the fragments which pass through the first b, proceed by an inclined conduit on to the second grate c, and so in succession. (See the conduits l, o, p). In front, and on a level with each of the grates b, c, d, &c., a child is stationed on one of the floors, 1, 2, 3, to 7. A current of water, which falls into the chest a, carries the fragments of ore upon the grates. The pieces which remain upon the two grates b and c, are thrown on the adjoining table v, where they undergo a sorting by hand; there the pieces are classified, 1. into gangue to be thrown away; 2. into ore for the stamp mill; 3. into ore to be sent directly to the furnace. The pieces which remain on each of the succeeding grates, d, e, f, g, h, are deposited on those of the floors 3 to 7, in front of each. Before every one of these shelves a deposit-sieve is established, (see t, u,) and the workmen in charge of it stand in one of the corresponding boxes, marked 8 to 12. The sieve is represented only in front of the chest h, for the sake of clearness. Each of the workmen placed in 8, 9, 10, 11, 12, operates on the heap before him; the upper layer of the deposit formed in his sieve, is sent to the stamping house, and the inferior layer directly to the furnace. As to the grains which, after traversing the five grates, have arrived at the chest x, they are washed in the two chests y, which are analogous to the German chests to be presently described. The upper layer of what is deposited in y is sent to the furnace; the rest is treated anew on three tables of percussion, similar to the English brake-sieves, also to be presently described. After several successive manipulations on these tables, an upper stratum of schlich is obtained fit for the furnace; an intermediate stratum, which is washed anew by the same process; and an inferior stratum, that is sent to the system of stamps, fig. 672. Fig. 672 enlarged (128 kB) This figure represents the general ground plan of a stamping and washing mill. The stamps F are composed of two batteries similar to fig. 670. The ore passes in succession under three pestles of cast iron, each of which is heavier the nearer it is to the sieve through which the sand or pounded matter escapes. In the upper part of the figure we see issuing from the stamps, two conduits destined to receive the water and the metalliferous sand with which it is loaded. The first, marked F, S, w, is used only when a certain quality of ore is stamped, richer in metal than is We shall now describe the percussion-tables used in the Hartz, for treating the sand of ore obtained from the conduits represented above. Figs. 673, 674. and 675. exhibit a plan, a vertical section, and elevation, of one of these tables, taken in the direction of its length. The arbor or great shaft in prolongation from the stamps mill, is shown in section perpendicularly to its axis, at A. The cams or wipers are shown round its circumference, one of them having just acted on n. These cams, by the revolution of the arbor, cause the alternating movements of a horizontal bar of wood o, u, which strikes at the point u against a table d, b, c, u. This table is suspended by two chains t, at its superior end, and by two rods at its lower end. After having been pushed by the piece o, u, it rebounds to strike against a block or bracket B. A lever p, q, serves to adjust the inclination of the movable table, the pivots q being points of suspension. The ore-sand to be washed, is placed in the chest a, into which a current of water runs. The ore floated onwards by the water, is carried through a sieve on a sloping small table x, under which is concealed the higher end of the movable table d, b, c, u; and it thence falls on this table, diffusing itself uniformly over its surface. The particles deposited on this table form an oblong talus (slope) upon it; the successive percussions that it receives, determine the weightier matters, and consequently those richest in metal, to accumulate towards its upper end at u. Now the workman by means of the lever p, raises the lower end d a little in order to preserve the same Fig. 676. is a profile of a plan which has been advantageously substituted, in the Hartz, for that part of the preceding apparatus which causes the jolt of the piece o u against the table d b c u. By means of this plan, it is easy to vary, according to the circumstances of a manipulation always delicate, the force of percussion which a bar x y, ought to communicate by its extremity y. With this view, a slender piece of wood u is made to slide in an upright piece, v x, adjusted upon an axis at v. To the piece u a rod of iron is connected, by means of a hinge z; this rod is capable of entering more or less into a case or sheath in the middle of the piece v x, and of being stopped at the proper point, by a thumb-screw which presses against this piece. If it be wished to increase the force of percussion, we must lower the point z; if to diminish it, we must raise it. In the first case, the extremity of the piece u, advances so much further under the cam of the driving shaft t; in the second, it goes so much less forwards; whereby the adjustment is produced. Figs. 677. and 678. represent a complete system of sleeping tables, tables dormantes; such as are mounted in Idria. Fig. 678. is the plan, and fig. 677. a vertical section. The mercurial ores, reduced to a sand by stamps like those of fig. 672., pass into a series of conduits a a, b b, c c, which form three successive floors below the level of the floor of the works. The sand taken out of these conduits is thrown into the cells q; whence they are transferred into the trough e, and water is run upon them by turning two stopcocks for each trough. The sand thus diffused upon each table, runs off with the water by a groove f, comes upon a sieve h, spreads itself upon the board g, and thence falls into the slanting chest, or sleeping table i k. The under surface k of this chest is pierced with holes, which may be stopped at pleasure with wooden plugs. There is a conduit m, at the lower end of each table, to catch the light particles carried off by the water out of the chest i k, through the holes properly opened, while the denser parts are deposited upon the bottom of this chest. A general conduit n passes across at the foot of all the chests i k; it receives the refuse of the washing operations. Fig. 679 enlarged (83 kB) Fig. 679. is a set of stamping and washing works for the ores of argentiferous galena, as mounted at Bockwiese, in the district of Zellerfeldt, in the Hartz. A is the stamp mill and its subsidiary parts; among which are a, the driving or The German chests are rectangular, being about 3 yards long, half a yard broad, with edges half a yard high; and their inclination is such that the lower end is about 15 inches beneath the level of the upper. At their upper end, usually called the bolster, a kind of trough or box, without any edge at the side next the chest, is placed, containing the ore to be washed. The water is allowed to fall upon the bolster in a thin sheet. The sleeping tables have upright edges; they are from 4 to 5 yards long, nearly 2 yards wide, and have fully a yard of inclination. The preceding tables are sometimes covered with cloth, particularly in treating ores that contain gold, on a supposition that the woollen or linen fibres would retain more surely the metallic particles; but this method appears on trial to merit no confidence, for it produces a very impure schlich. Fig. 680. is a swing-sieve employed in the Hartz, for sifting the small fragments of the ore of argentiferous lead. Such an apparatus is usually set up in the outside of a stamp, and washing mill; its place being denoted by the letter A, fig. 672. The two movable chests or boxes A B, of the sieve, are connected together, at their lower ends, with an upright rod, which terminates at one of the arms of a small balance beam, mounted between the driving shaft of the stamps and the sieve, perpendicularly to the length of both. The opposite arm of this beam carries another upright rod, which ears (cams or mentonnets), placed on purpose upon the driving shaft, may push down. During this movement the two lower ends A, B, are raised; and when the peg-cam of the shaft quits the rod which it had depressed, the swing chests fall by their own weight. Thus they In certain mines of the Hartz, tables called À balais, or sweeping tables, are employed. The whole of the process consists in letting flow, over the sloping table, in successive currents, water charged with the ore, which is deposited at a less or greater distance, as also pure water for the purpose of washing the deposited ore, afterwards carried off by means of this sweeping operation. At the upper end of these sweep-tables, the matters for washing are agitated in a chest, by a small wheel with vanes, or flap-boards. The conduit of the muddy waters opens above a little table or shelf; the conduit of pure water, which adjoins the preceding, opens below it. At the lower part of each of these tables, there is a transverse slit, covered by a small door with hinges, opening outwardly, by falling back towards the foot of the table. The water spreading over the table, may at pleasure be let into this slit, by raising a bit of leather which is nailed to the table, so as to cover the small door when it is in the shut position; but when this is opened, the piece of leather then hangs down into it. Otherwise the water may be allowed to pass freely above the leather, when the door is shut. The same thing may be done with a similar opening placed above the conduit. By means of these two slits, two distinct qualities of schlich may be obtained, which are deposited into two distinct conduits or canals. The refuse of the operation is turned into another conduit, and afterwards into ulterior reservoirs, whence it is lifted out to undergo a new washing. In the percussion tables, the water for washing the ores is sometimes spread in slender streamlets, sometimes in a full body, so as to let two cubic feet escape per minute. The number of shocks communicated per minute, varies from 15 to 36; and the table may be pushed out of its settled position at one time, three quarters of an inch, at another nearly 8 inches. The coarse ore-sand requires in general less water, and less slope of table, than the fine and pasty sand. The mechanical operations which ores undergo, take place commonly at their out-put from the mine, and without any intermediate operation. Sometimes, however, the hardness of certain gangues (vein-stones), and of certain iron-ores, is diminished by subjecting them to calcination previously to the breaking and stamping processes. When it is intended to wash certain ores, an operation founded on the difference of their specific gravities, it may happen that by slightly changing the chemical state of the substances that compose the ore, the earthy parts may become more easily separable, as also the other foreign matters. With this view, the ores of tin are subjected to a roasting, which by separating the arsenic, and oxidizing the copper which are intermixed, furnishes the means of obtaining, by the subsequent washing, an oxide of tin much purer than could be otherwise procured. In general, however, these are rare cases; so that the washing almost always immediately succeeds the picking and stamping; and the roasting comes next, when it needs to be employed. The operation of roasting is in general executed by various processes, relatively to the nature of the ores, the quality of the fuel, and to the object in view. The greatest economy ought to be studied in the fuel, as well as the labour; two most important circumstances, on account of the great masses operated upon. Three principal methods may be distinguished; 1. the roasting in a heap in the open air, the most simple of the whole; 2. the roasting executed between little walls, and which may be called case-roasting (rost-stadeln, in German); and 3. roasting in furnaces. We may remark, as to the description about to be given of these different processes, that in the first two, the fuel is always in immediate contact with the ore to be roasted, whilst in furnaces, this contact may or may not take place. 1. The roasting in the open air, and in heaps more or less considerable, is practised upon iron ores, and such as are pyritous or bituminous. The operation consists in general in spreading over a plane area, often bottomed with beaten clay, billets of wood arranged like the bars of a gridiron, and sometimes laid crosswise over one another, so as to form a uniform flat bed. Sometimes wood charcoal is scattered in, so as to fill up the interstices, and to prevent the ore from falling between the other pieces of the fuel. Coal is also employed in moderately small lumps; and even occasionally, turf. The ore either simply broken into pieces, or even sometimes under the form of schlich, is piled up over the fuel; most usually alternate beds of fuel and ore are formed. The fire, kindled in general at the lower part, but sometimes, however, at the middle chimney, spreads from spot to spot, putting the operation in train. The combustion must be so conducted as to be slow and suffocated, to prolong the ustulation, and let the whole mass be equably penetrated with heat. The means employed to direct the fire, are to cover outwardly with earth the portions where too much activity is displayed, and to pierce with holes or to give air to those where it is imperfectly developed. Rains, winds, variable seasons, and especially good primary arrangements of a calcination, have much influence on this process, which requires, besides, an almost incessant inspection at the beginning. Nothing in general can be said as to the consumption of fuel, because it varies with its quality, as well as with the ores and the purpose in view. But it may be laid down as a good rule, to employ no more fuel than is strictly necessary for the kind of calcination in hand, and for supporting the combustion; for an excess of fuel would produce, besides an expense uselessly incurred, the inconvenience, at times very serious, of such a heat as may melt or vitrify the ores; a result entirely the reverse of a well-conducted ustulation. Figs. 681, 682, 683. represent the roasting in mounds, as practised near Goslar in the Hartz, and at Chessy in the department of the Rhone. Fig. 681. is a vertical section in the line h c of figs. 682. and 683. In fig. 682. there is shown in plan, only a little more than one half of the quadrangular truncated pyramid, which constitutes the heap. Fig. 683. shows a little more than one fourth of a bed of wood, arranged at the bottom of the pyramid, as shown by a a, fig. 681., and c g h, fig. 683. C is a wooden chimney, formed within the heap of ore, at whose bottom c there is a little parcel of charcoal, d d are large lumps of ore distributed upon the wooden pile a a; e e are smaller fragments, to cover the larger; f f is rubbish and clay laid smoothly in a slope over the whole. g, fig. 683., a passage for air left under the bed of billets; of which there is a similar one in each of the four sides of the base a a, so that two principal currents of air cross under the upright axis C c, of the truncated pyramid indicated in fig. 681. The kindling is thrown in by the chimney C. The charcoal c, and the wood a a, take fire; the sulphureous ores d e f are heated to such a high temperature as to vaporize the sulphur. In the Lower Hartz, a heap of this kind continues roasting during four months. 2. The second method. The difficulty of managing the fire in the roasting of substances containing little sulphur, with the greater difficulty of arranging and supporting in their place the schlichs to be roasted, and last of all, the necessity of giving successive fires to the same ores, or to inconsiderable quantities at a time, have led to the contrivance of surrounding the area on which the roasting takes place with three little walls, or with four, leaving a door in the one in front. This is what is called a walled area, and sometimes, improperly enough, a roasting furnace. Inside of these little walls, about 3 feet high, there are often vertical conduits or chimneys made to correspond with an opening on the ground level, in order to excite a draught of air in the adjacent parts. When the roasting is once set agoing, these chimneys can be opened or shut at their upper ends, according to the necessities of the process. Several such furnaces are usually erected in connexion with each other by their lateral walls, and all terminated by a common wall, which forms their posterior part; sometimes they are covered with a shed supported partly by the back wall, built sufficiently high for this purpose. These dispositions are suitable for the roasting of schlichs, and in general of all matters which are to have several fires; a circumstance often indispensable to a due separation of the sulphur, arsenic, &c. 3. The furnaces employed for roasting the ores and the mattes differ much, according When iron ores are to be roasted, which require but a simple calcination to disengage the combined water and carbonic acid, egg-shaped furnaces, similar to those in which limestone is burned in contact with fuel, may be conveniently employed; and they present the advantage of an operation which is continuous with a never-cooling apparatus. The analogy in the effects to be produced is so perfect, that the same furnace may be used for either object. Greater dimensions may, however, be given to those destined for the calcination of iron ores. But it must be remembered that this process is applicable only to ores broken into lumps, and not to ores in grains or powder. It has been attempted to employ the same method a little modified, for the roasting of ores of sulphuret of copper and pyrites, with the view of extracting a part of the sulphur. More or less success has ensued, but without ever surmounting all the obstacles arising from the great fusibility of the sulphuret of iron. For sometimes it runs into one mass, or at least into lumps agglutinated together in certain parts of the furnace, and the operation is either stopped altogether, or becomes more or less languid; the air not being able to penetrate into all the parts, the roasting becomes consequently imperfect. This inconvenience is even more serious than might at first sight appear; for, as the ill-roasted ores now contain too little sulphur to support their combustion, and as they sometimes fall into small fragments in the cooling, they cannot be passed again through the same furnace, and it becomes necessary to finish the roasting in a reverberatory hearth, which is much more expensive. In the Pyrenees, the roasting of iron ores is executed in a circular furnace, so disposed that the fuel is contained and burned in a kind of interior oven, above which lie the pieces of ore to be calcined. Sometimes the vault of this oven which sustains the ore, is formed of bricks, leaving between them openings for the passage of the flame and the smoke, and the apparatus then resembles certain pottery kilns; at other times the vault is formed of large lumps of ore, carefully arranged as to the intervals requisite to be left for draught over the arch. The broken ore is then distributed above this arch, care being taken to place the larger pieces undermost. This process is simple in the construction of the furnace, and economical, as branches of trees, without value in the forests, may be employed in the roasting. See Lime-kiln figures. In some other countries, the ores are roasted in furnaces very like those in which porcelain is baked; that is to say, the fuel is placed exteriorly to the body of the furnace in a kind of brick shafts, and the flame traverses the broken ore with which the furnace is filled. In such an apparatus the calcination is continuous. When it is proposed to extract the sulphur from the iron pyrites, or from pyritous minerals, different furnaces may be employed, among which that used in Hungary deserves notice. It is a rectangular parallelopiped of four walls, each of them being perforated with holes and vertical conduits which lead into chambers of condensation, where the sulphur is collected. The ore placed between the four walls on billets of wood arranged as in figs. 681, 682, 683., for the great roastings in the open air, is calcined with the disengagement of much sulphur, which finds more facility in escaping by the lateral conduits in the walls, than up through the whole mass, or across the upper surface covered over with earth; whence it passes into the chambers of condensation. In this way upwards of a thousand tons of pyrites may be roasted at once, and a large quantity of sulphur obtained. See Copper. Roasting of Pyrites.—Figs. 684, 685. represent a furnace which has been long employed at Fahlun in Sweden, and several other parts of that kingdom, for roasting iron pyrites in order to obtain sulphur. This apparatus was constructed by the celebrated Gahn. Fig. 684. is a vertical section, in the line k d n o of fig. 685., which is a plan of the furnace; the top being supposed to be taken off. In both figures the conduit may be imagined to to be broken off at e; its entire length in a straight line is 43 feet beyond the dotted line e n, before the bend, which is an extension of this conduit. Upon the slope a b of a hillock a b c, lumps r of iron pyrites are piled upon the pieces of wood i i for roasting. A conduit d f e forms the continuation of the space denoted by r, which is covered by stone slabs so far as f; and from this point to the chamber h it is constructed in boards. At the beginning of this conduit, there is a recipient g. The chamber h is divided into five chambers by horizontal partitions, which permit the circulation of the The reverberatory furnace affords one of the best means of ustulation, where it is requisite to employ the simultaneous action of heat and atmospherical air to destroy certain combinations, and to decompose the sulphurets, arseniurets, &c. It is likewise evident that the facility thus offered of stirring the matters spread out on the sole, in order to renew the surfaces, of observing their appearances, of augmenting or diminishing the degree of heat, &c., promise a success much surer, a roasting far better executed, than by any other process. It is known, besides, that flame mingled with much undecomposed air issuing from the furnace, is highly oxidizing, and is very fit for burning away the sulphur, and oxidizing the metals. Finally, this is almost the only method of rightly roasting ores which are in a very fine powder. If it be not employed constantly and for every kind of ore, it is just because more economy is found in practising calcination in heaps, or on areas enclosed by walls; besides, in certain mines, a very great number of these furnaces, and many workmen, would be required to roast the considerable body of ores that must be daily smelted. Hence there would result from the construction of such apparatus and its maintenance a very notable outlay, which is saved in the other processes. But in every case where it is desired to have a very perfect roasting, as for blende from which zinc is to be extracted, for sulphuret of antimony, &c., or even for ores reduced to a very fine powder, and destined for amalgamation, it is proper to perform the operation in a reverberatory furnace. When very fusible sulphurous ores are treated, the workman charged with the calcination must employ much care and experience, chiefly in the management of the fire. It will sometimes, indeed, happen, that the ore partially fuses; when it becomes necessary to withdraw the materials from the furnace, to let them cool and grind them anew, in order to recommence the operation. The construction of these furnaces demands no other attention than to give to the sole or laboratory the suitable size, and so to proportion to this the grate and the chimney that the heating may be effected with the greatest economy. The reverberatory furnace is always employed to roast the ores of precious metals, and especially those for amalgamation; as the latter often contain arsenic, antimony, and other volatile substances, they must be disposed of in a peculiar manner. The sole, usually very spacious, is divided into two parts, of which the one farthest off from the furnace is a little higher than the other. Above the vault there is a space or chamber in which the ore is deposited, and which communicates with the laboratory by a vertical passage; which serves to allow the ore to be pushed down, when it is dried and a little heated. The flame and the smoke which escape from the sole or laboratory pass into condensing chambers, before entering into the chimney of draught, so as to deposit in them the oxide of arsenic and other substances. When the ore on the part of the sole farthest from the grate has suffered so much heat as to begin to be roasted, has became less fusible, and when the roasting of that in the nearer part of the sole is completed, the former is raked towards the fire-bridge, and its ustulation is finished by stirring it over frequently with a paddle, skilfully worked, through one of the doors left in the side for this purpose. The operation is considered to be finished when the vapours and the smell have almost wholly ceased; its duration depending obviously on the nature of the ores. When this furnace is employed to roast very arsenical ores, as the tin ores of Schlackenwald in Bohemia, and at Ehrenfriedersdorf in Saxony, the arsenical pyrites of Geyer (in Saxony), &c., the chambers of condensation for the arsenious acid are much more extensive than in the furnaces commonly used for roasting galena, copper, or even silver ores. Figs. 686, 687, 688. represent a reverberatory furnace employed in the smelting works of Lautenthal, in the Hartz, for roasting the schlichs of lead ores, which contain much blende or sulphuret of zinc. In fig. 686. we see that the two parts A B, B C, are absolutely like, the two furnaces being built in one body of brickwork. Fig. 687. is the plan of the furnace B C, taken at the level E F of fig. 686. Fig. 688. is a vertical section of the similar furnace A B, taken in the prolongation of the line G H in fig. 687. a is the fire-place of the furnace, its grate and ash-pit. b is the conduit of vaporization, which communicates with the chambers c; c, chambers into which the vaporized substances are deposited; d, chimney for the escape of the smoke of the fire-place a, after it has gone through the space b c c; e', is the charging door, with a hook hanging in front to rest the long iron rake upon, with which the materials are turned over; f, chamber containing a quantity of schlich destined for roasting; this chamber communicates with the vaulted corridor (gallery) D, seen in fig. 686.; g, orifice through which the schlich is thrown into the furnace; h, area or hearth of the reverberatory furnace, of which the roof is certainly much too high; i, channels for the escape of the watery vapours; k l, front arcade, between which and the furnace, properly speaking, are the two orifices of the conduits, which terminate at the channels m, m'. m is the channel for carrying towards the chimney d, the vapours which escape by the door e'. n is a walled-up door, which is opened from time to time, to take out of the chambers c, c, the substances that may be deposited in them. At the smelting works of Lautenthal, in such a roasting furnace, from 6 to 9 quintals (cwts.) of schlich are treated at a time, and it is stirred frequently with an iron rake upon the altar h. The period of this operation is from 6 to 12 hours, according as the schlich may be more or less dry, more or less rich in lead, or more or less charged with blende. When the latter substance is abundant, the process requires 12 hours, with about 60 cubic feet of cleft billets for fuel. In such furnaces are roasted the cobalt ores of Schneeberg in Saxony, the tin ores of Schlackenwald in Bohemia, of Ehrenfriedersdorf in Saxony, and elsewhere; as also the arsenical pyrites at Geyer in Saxony. But there are poison towers and extensive condensing chambers attached in the latter case. See Arsenic. Figs. 689, 690, 691. represent the reverberatory furnace generally employed in the Hartz, in the district of Mansfeldt, Saxony, Hungary, &c., for the treatment of black copper, and for refining rose copper upon the great scale. An analogous furnace is used at Andreasberg for the liquefaction or purification of the mattes, and for workable lead when it is much loaded with arsenic. Fig. 689. presents the elevation of the furnace parallel to the line I K, of the plan fig. 690.; which plan is taken at the level of the tuyÈre n, of fig. 691.; fig. 691. is a vertical section in the line L M, fig. 690. k represents one of two basins of reception, brasqued with clay and charcoal; n, n, two tuyÈres, through which enters the blast of two pairs of bellows, like those shown at Cupellation of Silver; q, door by which the matter to be melted is laid upon the sole of the furnace; v, v, two points where the sole is perforated, when necessary to run off the melted matter into either of the basins h; x, door through which the slags or cinders floating upon the surface Figs. 692, 693, 694., show the furnace employed for liquation in one of the principal smelting works of the Hartz. Fig. 694. exhibits the working area charged with the liquation cakes and charcoal, supported by sheets of wrought iron; being an image of the process in action. Fig. 693. is the plan, in the line F, G, of fig. 692. A liquation cake is composed of— Black copper holding at least 5 or 6 loths (21/2 or 3 oz.) of silver per cwt., and weighing 90 to 96 lbs. Lead obtained from litharge, 2 cwts. Litharge, 1/2 cwt. From 30 to 32 cakes are successively worked in one operation, which lasts about 5 hours; the furnace is brought into action, as usual, with the aid of slags; then a little litharge is added; when the lead begins to flow, the copper is introduced, and when the copper flows, lead is added, so that the mixture of the metals may be effected in the best way possible. From 8 to 16 of these cakes (pains) are usually placed in the liquation furnace, figs. 692, 693, 694. The operation lasts 3 or 4 hours, in which time about 11/2 quintals of charcoal are consumed. The cakes are covered with burning charcoal, supported, as I have said, by the iron plates. The workable lead obtained flows off towards the basin in front of the furnace; whence it is laded out into moulds set alongside. See fig. 693. If the lead thus obtained be not sufficiently rich in silver to be worth cupellation, it is employed to form new liquation cakes. When it contains from 5 to 6 loths of silver per cwt., it is submitted to cupellation in the said smelting works. See Silver. The trompe, or water-blowing engine, figs. 695, 696, 697. Fig. 695. is the elevation; fig. 696. is a vertical section, made at right angles to the elevation. The machine is formed of two cylindrical pipes, the bodies of the trompe b b, set upright, called the funnels, which terminate above in a water cistern a, and below in a close basin under c, called the tub or The air-pipe e f, fig. 696., is fitted to the upper part of the drum; it is divided, at the point f, into three tubes, of which the principal one is destined for the furnace of cupellation, whilst the other two g g, serve for different melting furnaces. Each of these tubes ends in a leather pocket, and an iron nose-pipe k, adjusted in the tuyÈre of the furnace. At Pesey, and in the whole of Savoy, a floodgate is fitted into the upper cistern a, to regulate the admission of water into the trome; but in Carniola, the funnel p is closed with a wooden plug, suspended to a cord, which goes round a pulley mounted upon a horizontal axis, as shewn in fig. 697. By the plug a being raised more or less, merely the quantity of water required for the operation is admitted. The plug is pierced lengthwise with an oblique hole c c, in which the small tube c is inserted, with its top some way above the water level, through which air may be admitted into the heart of the column descending into the trompe p q. The ordinary height of the trompe apparatus is about 26 or 27 feet to the upper level of the water cistern; its total length is 11 mÈtres (36 feet 6 inches), and its width 2 feet, to give room for the drums. It is situated 10 mÈtres (331/3 feet) from the melting furnace. This is the case at the smelting works of Jauerberg, in Upper Carniola. OF THE ASSAY OF ORES. Assays ought to occupy an important place in metallurgic instructions, and there is By the title Assays, in a metallurgic point of view, is meant the method of ascertaining for any substance whatever, not only the presence and the nature of a metal, but its proportional quantity. Hence the operations which do not lead to a precise determination of the metal in question, are not to be arranged among the assays now under consideration. Experiments made with the blow-pipe, although capable of yielding most useful indications, are like the touchstone in regard to gold, and do not constitute genuine assays. Three kinds of assays may be practised in different circumstances, and with more or less advantage upon different ores. 1. The mechanical assay; 2. the assay by the dry way; 3. the assay by the humid way. 1. Of mechanical assays.—These kinds of assays consist in the separation of the substances mechanically mixed in the ores, and are performed by a hand-washing, in a small trough of an oblong shape, called a sebilla. After pulverizing with more or less pains the matters to be assayed by this process, a determinate weight of them is put into this wooden bowl with a little water; and by means of certain movements and some precautions, to be learned only by practice, the lightest substances may be pretty exactly separated, namely, the earthy gangues from the denser matter or metallic particles, without losing any sensible portion of them. Thus a schlich of greater or less purity will be obtained, which may afford the means of judging by its quality of the richness of the assayed ores, and which may thereafter be subjected to assays of another kind, whereby the whole metal may be insulated. Washing, as an assay, is practised on auriferous sands; on all ores from the stamps, and even on schlichs already washed upon the great scale, to appreciate more nicely the degree of purity they have acquired. The ores of tin in which the oxide is often disseminated in much earthy gangue, are well adapted to this species of assay, because the tin oxide is very dense. The mechanical assay may also be employed in reference to the ores whose metallic portion presents an uniform composition, provided it also possesses considerable specific gravity. Thus the ores of sulphuret of lead (galena) being susceptible of becoming almost pure sulphurets (within 1 or 2 per cent.) by mere washing skilfully conducted, the richness of that ore in pure galena, and consequently in lead, may be at once concluded; since 120 of galena contain 104 of lead, and 16 of sulphur. The sulphuret of antimony mingled with its gangue may be subjected to the same mode of assay, and the result will be still more direct, since the crude antimony is brought into the market after being freed from its gangue by a simple fusion. The assay by washing is also had recourse to for ascertaining if the scoriÆ or other products of the furnaces contain some metallic grains which might be extracted from them by stamping and washing on the great scale; a process employed considerably with the scoriÆ of tin and copper works. Of assays by the dry way.—The assay by the dry way has for its object, to show the nature and proportion of the metals contained in a mineral substance. To make a good assay, however, it is indispensably necessary to know what is the metal associated with it, and even within certain limits, the quantity of the foreign bodies. Only one metal is commonly looked after; unless in the case of certain argentiferous ores. The mineralogical examination of the substances under treatment, is most commonly sufficient to afford data in these respects; but the assays may always be varied with different views, before stopping at a definite result; and in every instance, only such assays can be confided in, as have been verified by a double operation. This mode of assaying requires only a little experience, with a simple apparatus; and is of such a nature as to be practised currently in the smelting works. The air furnace and crucibles employed are described in all good elementary chemical books. These assays are usually performed with the addition of a flux to the ore, or some agent for separating the earthy from the metallic substances; and they possess a peculiar advantage relative to the smelting operations, because they offer many analogies between results on the great scale and experiments on the small. This may even enable us often to deduce, from the manner in which the assay has succeeded with a certain flux, and at a certain degree of heat, valuable indications as to the treatment of the ore in the great way. See Furnace. In the smelting houses which purchase the ore, as in Germany, it is necessary to bestow much attention upon the assays, because they serve to regulate the quality and In the central works of the Hartz, as well as in those of Saxony, the schlichs as delivered are subjected to docimastic assays, which are verified three times, and by three different persons, one of whom is engaged for the interests of the mining partners, another for that of the smelting house, and a third as arbiter in case of a difference. If the first two results of assaying differ by 1/2 loth (or 1/4 ounce) of silver per cwt. of schlich, the operations must be resumed; but this rarely happens. When out of the three assays, the one differs from the two others by no more than 1/4 loth of silver per cwt., but by more in one, and by less in another, the mean result is adopted. As to the contents of the schlich in lead, the mean results of the assays must be taken. The differences allowed, are three pounds for the schlich, when it contains from 12 to 30 per cent. of lead, increasing to six pounds for schlich, when it contains less than 55 per cent. of that metal. Assaying forms in great establishments, an important object in reference to time and expense. Thus, in the single work of Franckenscharn, in the Hartz, no less than 300 assays have to be made in a threefold way, every Monday, without taking into account the several assays of the smelting products which take place every Thursday. Formerly fluxes more or less compound were employed for these purposes, and every assay cost about fifteen pence. At present all these assays are made more simply, by much cheaper methods, and cost a penny farthing each upon an average. Of the assays by the humid way.—The assays by the humid way, not reducible to very simple processes, are true chemical analyses, which may in fact be applied with much advantage, either to ores, or to the products of the furnace; but which cannot be expected to be practised in smelting-houses, on account of the complication of apparatus and reagents they require. Moreover, an expert chemist is necessary to obtain results that can be depended on. The directors of smelting-houses, however, should never neglect any opportunities that may occur of submitting the materials operated upon, as well as their products, to a more thorough examination than the dry way alone can effect. One of the great advantages of similar researches is, to discover and appreciate the minute quantities of injurious substances which impair the malleability of the metals, which give them several bad qualities, about whose nature and cause, more or less error and uncertainty prevail. Chemical analysis, rightly applied to metallurgy, cannot fail to introduce remarkable improvements into the processes.—See the different metals, in their alphabetical places. For assays in the dry way, both of stony and metallic minerals, the process of Dr. Abich deserves recommendation. In consists in mixing the pulverized mineral with 4 or 6 times its weight of carbonate of baryta in powder, fusing the mixture at a white heat, and then dissolving it after it cools, in dilute muriatic acid. The most refractory minerals, even corundum, cyanite, staurolite, zircon, and felspar, yield readily to this treatment. This process may be employed with advantage upon poor refractory ores. The platinum crucible, into which the mixed materials are put for fusion, should be placed in a Hessian crucible, and surrounded with good coak. The following tabular view of the metallic produce of the British mines, is given by two very skilful observers, in a work published in 1827, entitled Voyage Metallurgique en Angleterre, par MM. DufrÉnoy et Elie de Beaumont:—
The manganese raised in England exceeds 2000 tons. M. Heron de Villefosse inserted in the last number of the Annales des Mines for 1827, the following statistical view of the metallic products of France:—
The total value of which is estimated at 80 millions of francs; or about 3,400,000 pounds sterling. 1. They are all, more or less, remarkable for a peculiar lustre, called the metallic. This property of strongly reflecting light, is connected with a certain state of aggregation of their particles, but is possessed, superficially at least, by mica, animal charcoal, selenium, polished indigo;—bodies not at all metallic. 2. The metals are excellent conductors of caloric, and most of them also of electricity, though probably not all. According to Despretz, they possess the power of conducting heat according to the following numbers:—Gold, 1000; platinum, 981; silver, 973; copper, 898; iron, 374; zinc, 363; tin, 304; lead, 179·6. Becquerel gives the following table of metals, as to electrical conduction:— Copper, 100; gold, 93·6; silver, 73·6; zinc, 28·5; platina, 16·4; iron, 15·8; tin, 15·5; lead, 8·3; mercury, 3·5; potassium, 1·33. The metals which hardly, if at all, conduct electricity, are, zirconium; alumium; tantalum, in powder; and tellurium. 3. Metals are probably opaque; yet gold leaf, as observed by Newton, seems to transmit the green rays, for objects placed behind it in the sunbeam appear green. This phenomena has, however, been ascribed to the rays of light passing through an infinite number of minute fissures in the thinly hammered gold. 4. All metals are capable of combining with oxygen, but with affinities and in quantities extremely different. Potassium and sodium have the strongest affinity for it; arsenic and chromium, the feeblest. Many metals become acids by a sufficient dose of oxygen, while, with a smaller dose, they constitute salifiable bases. 5. Metals combine with each other, forming a class of bodies called alloys, except when one of them is mercury, in which case the compound is styled an amalgam. 6. They combine with hydrogen into hydrurets; with carbon, into carburets; with sulphur, into sulphurets; with phosphorus, into phosphurets; with selenium, into seleniurets; with boron, into borurets (borides?); with chlorine, into chlorides; with iodine, into iodides; with cyanogen, into cyanides; with silicon, into silicides; and with fluorine, into fluorides. 7. Metallic salts are definite compounds, mostly crystalline, of the metallic oxides with the acids. See Haloid. The mica of Fahlun, analyzed by Rose, afforded, silica, 46·22; alumina, 34·52; peroxide? of iron, 6·04; potash, 8·22; magnesia, with oxide of manganese, 2·11; fluoric acid, 1·09; water, 0·98.
When milk contained in wire-corked bottles, is heated to the boiling point in a water bath, the oxygen of the included small portion of air under the cork seems to be carbonated, and the milk will afterwards keep fresh, it is said, for a year or two; as green gooseberries and peas do by the same treatment. The Buhr-stones usually occur in beds, which are sometimes continuous, and at others interrupted. These beds are placed amid deposits of sand, or argillaceous and ferruginous marls, which penetrate between them, filling their fissures and honeycomb cavities. Buhr-stones constitute a very rare geological formation, being found in abundance only in the mineral basin of Paris, and a few adjoining districts. Its place of superposition is well ascertained: it forms a part of the lacustrine, or fresh-water formation, which, in the locality alluded to, lies above the fossil-bone gypsum, and the stratum of sand and marine sandstone which cover it. Buhr-stone constitutes, therefore, the uppermost solid stratum of the crust of the globe; for above it there is nothing but alluvial soil, or diluvial gravel, sand, and loam. Buhr-stones sometimes contain no organic forms, at others they seem as if stuffed full of fresh-water shells, or land shells and vegetables of inland growth. There is no exception known to this arrangement; but the shells have assumed a siliceous nature, and their cavities are often bedecked with crystals of quartz. The best Buhr-stones for grinding corn, have about an equal proportion of solid matter, and of vacant space. The finest quarry of them is upon the high ground, near La FertÉ-sous-Jouarre. The stones are quarried in the open air, and are cut out in cylinders, from one to two yards in diameter, by a series of iron and wooden wedges, gradually but equally inserted. The pieces of buhr-stones are afterwards cut into parallelopipeds, called panes, which are bound with iron hoops into large millstones. These pieces are exported chiefly to England and America. Good millstones of a bluish white colour, with a regular proportion of cells, when six feet and a half in diameter, fetch 1200 francs a-piece, or 48l. sterling. A coarse conglomerate sandstone or breccia is, in some cases, used as a substitute for buhr-stones; but it is a poor one. The stratiform deposits are subdivided into two great classes; the primary and the secondary. The former seem to have been called into existence before the creation of organic matter, because they contain no exuviÆ of vegetable or animal beings; while the latter are more or less interspersed, and sometimes replete with organic remains. The primary strata are characterized, moreover, by the nearly vertical or highly inclined position of their planes; the secondary lie for the most part in a nearly horizontal position. Where the primitive mountains graduate down into the plains, rocks of an intermediate character appear, which, though possessing a nearly vertical position, contain a few vestiges of animal beings, especially shells. These have been called transition, to indicate their being the passing links between the first and second systems of ancient deposits; they are distinguished by the fractured and cemented texture of their planes, for which reason they are sometimes called conglomerate. Between these and the truly secondary rocks, another very valuable series is interposed in certain districts of the globe; namely, the coal-measures, the paramount formation of Great Britain. The coal strata are disposed in a basin-form, and alternate with parallel beds of sandstone, slate-clay, iron-stone, and occasionally limestone. Some geologists have called the coal-measures the medial formation. In every mineral plane, the inclination and direction are to be noted; the former being the angle which it forms with the horizon, the latter the point of the azimuth or horizon, towards which it dips, as west, north-east, south, &c. The direction of the bed is that of a horizontal line drawn in its plane; and which is also denoted by the point of the compass. Since the lines of direction and inclination are at right angles to each other, the first may always be inferred from the second; for when a stratum is said to dip to the east or west, this implies that its direction is north and south. The smaller sinuosities of the bed are not taken into account, just as the windings of a river are neglected in stating the line of its course. Masses are mineral deposits, not extensively spread in parallel planes, but irregular heaps, rounded or oval, enveloped in whole or in a great measure by rocks of a different kind. Lenticular masses being frequently placed between two horizontal or inclined strata, have been sometimes supposed to be stratiform themselves, and have been accordingly denominated by the Germans liegende stocke, lying heaps or blocks. The orbicular masses often occur in the interior of unstratified mountains, or in the bosom of one bed. Nests, concretions, nodules, are small masses found in the middle of strata; the first being commonly in a friable state; the second often kidney-shaped, or tuberous; the third nearly round, and encrusted, like the kernel of an almond. Lodes, or large veins, are flattened masses, with their opposite surfaces not parallel, which consequently terminate like a wedge, at a greater or less distance, and do not run parallel with the rocky strata in which they lie, but cross them in a direction not far from the perpendicular; often traversing several different mineral planes. The lodes are sometimes deranged in their course, so as to pursue for a little way the space between two contiguous strata; at other times they divide into several branches. The matter which fills the lodes is for the most part entirely different from the rocks they pass through, or at least it possesses peculiar features. This mode of existence, exhibited by several mineral substances, but which has been long known with regard to metallic ores, suggests the idea of clefts or rents having been made in the stratum posterior to its consolidation, and of the vacuities having been filled with foreign matter, either immediately or after a certain interval. There can be no doubt as to the justness of the first part of the proposition, for there may be observed round many lodes undeniable proofs of the movement or dislocation of the rock; for example, upon each side of the rent, the same strata are no longer situated in the same plane as before, but make greater or smaller angles with it; or the stratum upon one side of the lode is raised considerably above, or depressed considerably below, its counterpart upon the other side. With regard to the manner in which the rent has been filled, different opinions may be entertained. In the lodes which are widest near the surface of the ground, and graduate into a thin wedge below, the foreign matter would seem to have been introduced as into a funnel at the top, and to have carried along with it in its fluid state portions of rounded gravel and organic remains. In other cases, other conceptions seem to be more probable; since many lodes are largest at their under part, and become progressively narrower as they approach the surface; from which circumstance, it has been inferred that the rent has been caused by an In the lodes, the principal matters which fill them are to be distinguished from the accessory substances; the latter being distributed irregularly, amidst the mass of the first, in crystals, nodules, grains, seams, &c. The non-metalliferous exterior portion, which is often the largest, is called gangue, from the German gang, vein. The position of a vein is denoted, like that of the strata, by the angle of inclination, and the point of the horizon towards which they dip, whence the direction is deduced. Veins, are merely small lodes, which sometimes traverse the great ones, ramifying in various directions, and in different degrees of tenuity. A metalliferous substance is said to be disseminated, when it is dispersed in crystals, spangles, scales, globules, &c., through a large mineral mass. Certain ores which contain the metals most indispensable to human necessities, have been treasured up by the Creator in very bountiful deposits; constituting either great masses in rocks of different kinds, or distributed in lodes, veins, nests, concretions, or beds with stony and earthy admixtures; the whole of which become the objects of mineral exploration. These precious stores occur in different stages of the geological formations; but their main portion, after having existed abundantly in the several orders of the primary strata, suddenly cease to be found towards the middle of the secondary. Iron ores are the only ones which continue among the more modern deposits, even so high as the beds immediately beneath the chalk, when they also disappear, or exist merely as colouring matters of the tertiary earthy beds. The strata of gneiss and mica-slate constitute in Europe the grand metallic domain. There is hardly any kind of ore which does not occur there in sufficient abundance to become the object of mining operations, and many are found no where else. The transition rocks and the lower part of the secondary ones, are not so rich, neither do they contain the same variety of ores. But this order of things, which is presented by Great Britain, Germany, France, Sweden, and Norway, is far from forming a general law; since in equinoxial America the gneiss is but little metalliferous; while the superior strata, such as the clay-schists, the sienitic porphyries, the limestones, which complete the transition series, as also several secondary deposits, include the greater portion of the immense mineral wealth of that region of the globe. All the substances of which the ordinary metals form the basis, are not equally abundant in nature; a great proportion of the numerous mineral species which figure in our classifications, are mere varieties scattered up and down in the cavities of the great masses or lodes. The workable ores are few in number, being mostly sulphurets, some oxides, and carbonates. These occasionally form of themselves very large masses, but more frequently they are blended with lumps of quartz felspar, and carbonate of lime, which form the main body of the deposit; as happens always in proper lodes. The ores in that case are arranged in small layers parallel to the strata of the formation, or in small veins which traverse the rock in all directions, or in nests or concretions stationed irregularly, or finally disseminated in hardly visible particles. These deposits sometimes contain apparently only one species of ore, sometimes several, which must be mined together, as they seem to be of contemporaneous formation; whilst, in other cases, they are separable, having been probably formed at different epochs. In treating of the several metals in their alphabetical order, I have taken care to describe their peculiar geological positions, and the rocks which accompany or mineralize them. In mining, as in architecture, the best method of imparting instruction is to display the master-pieces of the respective arts, which speak clearly to the mind through the medium of the eye. It is not so easy, however, to represent at once the general effect of a mine, as it is of an edifice; because there is no point of sight from which the former can be sketched at once, like the latter. The subterraneous structures certainly afford some of the finest examples of the useful labours of man, continued for ages, under the guidance of science and ingenuity; but, however curious, beautiful, and grand in themselves, they cannot become objects of a panoramic view. It is only by the lights of geometry and geology that mines can be contemplated and surveyed, either as a whole or in their details; and, therefore, these marvellous subterranean regions, in which roads are cut 698. A general view of mining operations. As there is no country in the world so truly rich and powerful, by virtue of its mineral stores, as Great Britain, so there are no people who ought to take a deeper interest in their scientific illustration. I have endeavoured in the present article to collect from the most authentic sources the most interesting and instructive examples of mining operations. To the magnificent work of Ville-Fosse, Sur la Richesse Minerale, no longer on sale, I have to acknowledge weighty obligations; many of the figures being copied from his great Atlas. Lodes or mineral veins are usually distinguished by English miners into at least four species. 1. The rake vein. 2. The pipe vein. 3. The flat or dilated vein; and 4. The interlaced mass (stock-werke), indicating the union of a multitude of small veins mixed in every possible direction with each other, and with the rock. 1. The rake vein is a perpendicular mineral fissure; and is the form best known among practical miners. It commonly runs in a straight line, beginning at the superficies of the strata, and cutting them downwards, generally further than can be reached. This vein sometimes stands quite perpendicular; but it more usually inclines or hangs over at a greater or smaller angle, or slope, which is called by the miners the hade or hading of the vein. The line of direction in which the fissure runs, is called the bearing of the vein. 2. The pipe vein resembles in many respects a huge irregular cavern, pushing forward into the body of the earth in a sloping direction, under various inclinations, from an angle of a few degrees to the horizon, to a dip of 45°, or more. The pipe does not in general cut the strata across like the rake vein, but insinuates itself between them; so that if the plane of the strata be nearly horizontal, the bearing of the pipe vein will be conformable; but if the strata stand up at a high angle, the pipe shoots down nearly headlong like a shaft. Some pipes are very wide and high, others are very low and narrow, sometimes not larger than a common mine or drift. 3. The flat or dilated vein, is a space or opening between two strata or beds of stone, the one of which lies above, and the other below this vein, like a stratum of coal 4. The interlaced mass has been already defined. To these may be added the accumulated vein, or irregular mass (butzenwerke), a great deposit placed without any order in the bosom of the rocks, apparently filling up cavernous spaces. The interlaced masses are more frequent in primitive formations, than in the others; and tin is the ore which most commonly affects this locality. See figure of Tin mine. The study of the mineral substances, called gangues or vein-stones, which usually accompany the different ores, is indispensable in the investigation and working of mines. These gangues, such as quartz, calcareous spar, fluor spar, heavy spar, &c., and a great number of other substances, although of little or no value in themselves, become of great consequence to the miner, either by pointing out by their presence that of certain useful minerals, or by characterising in their several associations, different deposits of ores of which it may be possible to follow the traces, and to discriminate the relations, often of a complicated kind, provided we observe assiduously the accompanying gangues. Mineral veins are subject to derangements in their course, which are called shifts or faults. Thus, when a transverse vein throws out, or intercepts, a longitudinal one, we must commonly look for the rejected vein on the side of the obtuse angle which the direction of the latter makes with that of the former. When a bed of ore is deranged by a fault, we must observe whether the slip of the strata be upwards or downwards; for in either circumstance, it is only by pursuing the direction of the fault that we can recover the ore; in the former case by mounting, in the latter by descending beyond the dislocation. When two veins intersect each other, the direction of the offcast is a subject of interest, both to the miner and the geologist. In Saxony it is considered as a general fact that the portion thrown out is always upon the side of the obtuse angle, a circumstance which holds also in Cornwall; and the more obtuse the angle, the out-throw is the more considerable. A vein may be thrown out on meeting another vein, in a line which approaches either towards its inclination or its direction. The Cornish miners use two different terms to denote these two modes of rejection; for the first case, they say the vein is heaved; for the second, it is started. The great copper lode of Carharack, d, fig. 699. in the parish of Gwenap, is one of the most instructive examples of intersection. The power or thickness of this vein is 8 feet; its direction is nearly due east and west, and it dips towards the north at an inclination of two feet per fathom; its upper part being in the killas (a greenish clay-slate); its lower part in the granite. The lode has suffered two intersections; the first produced by meeting the vein h, called Steven’s fluckan, which runs from north-east to south-west, and which throws the lode several fathoms out; the second is produced by another vein i, almost at right angles with the first, and which occasions another out-throw of 20 fathoms to the right side. The fall of the vein occurs therefore in the one case to the right, and in the other to the left; but in both it is towards the side of the obtuse angle. This distribution is very singular; for one part of the vein appears to have mounted while the other has descended. N, S denotes North and South. d is the copper lode running east and west. h, i, are systems of clay-slate veins called fluckans; the line over S, represents the down-shift, and d' the up-shift. General observations on the localities of ores, and on the indications of metallic mines. 1. Tin, exists principally in primitive rocks, appearing either in interlaced masses, in beds, or as a constituent part of the rock itself, and more rarely in distinct veins. Tin ore is found indeed sometimes in alluvial land, filling up low situations between lofty mountains. 2. Gold, occurs either in beds, or in veins, frequently in primitive rocks; though in other formations, and particularly in alluvial earth, it is also found. When this metal exists in the bosom of primitive rocks, it is particularly in schists; it is not found in serpentine, but it is met with in greywacke in Transylvania. The gold of alluvial districts, 3. Silver, is found particularly in veins and beds, in primitive and transition formations; though some veins of this metal occur in secondary strata. The rocks richest in it are, gneiss, mica-slate, clay-slate, greywacke, and old alpine limestone. Localities of silver-ore itself are not numerous, at least in Europe, among secondary formations; but it occurs in combination with the ores of copper or of lead. 4. Copper, exists in the three mineral epochas; 1. in primitive rocks, principally in the state of pyritous copper, in beds, in masses, or in veins; 2. in transition districts, sometimes in masses, sometimes in veins of copper pyrites; 3. in secondary strata, especially in beds of cupreous schist. 5. Lead, occurs also in each of the three mineral epochas; abounding particularly in primitive and transition grounds, where it usually constitutes veins, and occasionally beds of sulphuretted lead (galena). The same ore is found in strata or in veins among secondary rocks, associated now and then with ochreous iron-oxide and calamine (carbonate of zinc); and it is sometimes disseminated in grains through more recent strata. 6. Iron, is met with in four different mineral eras, but in different ores. Among primitive rocks, magnetic iron ore and specular iron ore occur chiefly in beds, sometimes of enormous size; the ores of red or brown oxide of iron (hÆmatite) are found generally in veins, or occasionally in masses with sparry iron, both in primitive and transition rocks; as also sometimes in secondary strata; but more frequently in the coal-measure strata, as beds of clay-ironstone, of globular iron oxide, and carbonate of iron. In alluvial districts we find ores of clay-ironstone, granular iron-ore, bog-ore, swamp-ore, and meadow-ore. The iron ores which belong to the primitive period have almost always the metallic aspect, with a richness amounting even to 80 per cent. of iron, while the ores in the posterior formations become in general more and more earthy, down to those in alluvial soils, some of which present the appearance of a common stone, and afford not more than 20 per cent. of metal, though its quality is often excellent. 7. Mercury, occurs principally among secondary strata, in disseminated masses, along with combustible substances; though the metal is met with occasionally in primitive countries. 8. Cobalt, belongs to the three mineral epochas; its most abundant deposits are veins in primitive rocks; small veins containing this metal are found, however, in secondary strata. 9. Antimony, occurs in veins or beds among primitive and transition rocks. 10, 11. Bismuth and nickel do not appear to constitute the predominating substance of any mineral deposits; but they often accompany cobalt. 12. Zinc, occurs in the three several formations: namely, as sulphuret or blende, particularly in primitive and transition rocks; as calamine, in secondary strata, usually along with oxide of iron, and sometimes with sulphuret of lead. An acquaintance with the general results collected and classified by geology must be our first guide in the investigation of mines. This enables the observer to judge whether any particular district, should from the nature and arrangement of its rocks, be susceptible of including within its bosom, beds of workable ores; it indicates also, to a certain degree, what substances may probably be met with in a given series of rocks, and what locality these substances will preferably affect. For want of a knowledge of these facts, many persons have gone blindly into researches equally absurd and ruinous. Formerly indications of mines were taken from very unimportant circumstances; from thermal waters, the heat of which was gratuitously referred to the decomposition of pyrites; from mineral waters, whose course is however often from a far distant source; from vapours incumbent over particular mountain groups; from the snows melting faster in one mineral district than another; from the different species of forest trees, and from the greater or less vigour of vegetation, &c. In general, all such indications are equally fallacious with the divining rod, and the compass made of a lump of pyrites suspended by a thread. Geognostic observation has substituted more rational characters of metallic deposits, some of which may be called negative and others positive. The negative indications are derived from that peculiar geological constitution, which from experience or general principles excludes certain metallic matters; for example, granite, and in general every primitive formation, forbids the hope of finding within them combustible fossils (pit-coal), unless it be beds of anthracite; there also it would be vain to seek for sal gem. It is very seldom that granite rocks include silver; or limestones, ores of tin. Volcanic territories never afford any metallic ores worth the working; nor do extensive veins usually run into secondary and alluvial formations. The richer ores of iron do not occur in secondary strata; and the ores of this metal peculiar to these localities, do not exist among primary rocks. Among positive indications, some are proximate and others remote. The proximate are, an efflorescence, so to speak, of the subjacent metallic masses; magnetic attraction for iron ores; bituminous stone, or inflammable gas for pit-coal; the frequent occurrence of fragments of particular ores, &c. The remote indications consist in the geological epocha, and nature of the rocks. From the examples previously adduced, marks of this kind acquire new importance when in a district susceptible of including deposits of workable ores, the gangues or vein-stones are met with which usually accompany any particular metal. The general aspect of mountains whose flanks present gentle and continuous slopes, the frequency of sterile veins, the presence of metalliferous sands, the neighbourhood of some known locality of an ore, for instance that of iron-stone in reference to coal, lastly the existence of salt springs and mineral waters, may furnish some indications; but when ferruginous or cupreous waters issue from sands or clays, such characters merit in general little attention, because the waters may flow from a great distance. No greater importance can be attached to metalliferous sands and saline springs. In speaking of remote indications, we may remark that in several places, and particularly near Clausthal in the Hartz, a certain ore of red oxide of iron occurs above the most abundant deposits of the ores of lead and silver; whence it has been named by the Germans the iron-hat. It appears that the iron ore rich in silver, which is worked in America under the name of pacos, has some analogy with this substance; but iron ore is in general so plentifully diffused on the surface of the soil, that its presence can be regarded as only a remote indication, relative to other mineral substances, except in the case of clay ironstone with coal. Of the instruments and operations of subterranean operations.—It is by the aid of geometry in the first place that the miner studies the situation of the mineral deposits, on the surface and in the interior of the ground; determines the several relations of the veins and the rocks; and becomes capable of directing the perforations towards a suitable end. The instruments are, 1. the magnetic compass, which is employed to measure the direction of a metallic ore, wherever the neighbourhood of iron does not interfere with its functions; 2. the graduated semicircle which serves to measure the inclination, which is also called the clinometer. 3. The chain or cord for measuring the distance of one point from another. 4. When the neighbourhood of iron renders the use of the magnet uncertain, a plate or plane table is employed. The dials of the compasses generally used in the most celebrated mines, are graduated into hours; most commonly into twice 12 hours. Thus the whole limb is divided into 24 spaces, each of which contains 15° = 1 hour. Each hour is subdivided into 8 parts. Means of penetrating into the interior of the earth.—In order to penetrate into the interior of the earth, and to extract from it the objects of his toils, the miner has at his disposal several means, which may be divided into three classes: 1. manual tools, 2. gunpowder, and 3. fire. The tools used by the miners of Cornwall and Devonshire are the following: Fig. 700. The pick. It is a light tool, and somewhat varied in shape according to circumstances. One side used as a hammer is called the poll, and is employed to drive in the gads, or to loosen and detach prominences. The point is of steel, carefully tempered, and drawn under the hammer to the proper form. The French call it pointerolle. Fig. 701. The gad. It is a wedge of steel, driven into crevices of rocks, or into small openings made with the point of the pick. Fig. 702. The miner’s shovel. It has a pointed form, to enable it to penetrate among the coarse and hard fragments of the mine rubbish. Its handle being somewhat bent, a man’s power may be conveniently applied without bending his body. The blasting or shooting tools are:—
Besides these tools the miner requires a powder-horn, rushes to be filled with gunpowder, tin cartridges for occasional use in wet ground, and paper rubbed over with gunpowder or grease, for the smifts or fuses. The borer, fig. 704., is an iron bar tipped with steel, formed like a thick chisel, and is used by one man holding it straight in the hole with constant rotation on its axis, while another strikes the head of it with the iron sledge or mallet, fig. 703. The hole is cleared out from time to time by the scraper, fig. 707., which is a flat iron rod turned up at one end. If the ground be very wet, and the hole gets full of mud, it is cleaned out by a stick bent at the end into a fibrous brush, called a swab-stick. Fig. 709. represents the plan of blasting the rock, and a section of a hole ready for firing. The hole must be rendered as dry as possible, which is effected very simply by filling it partly with tenacious clay, and then driving into it a tapering iron rod, which nearly fills its calibre, called the claying bar. This being forced in with great violence, condenses the clay into all the crevices of the rock, and secures the dryness of the hole. Should this plan fail, recourse is had to tin cartridges furnished with a stem or tube (see fig. 710.,) through which the powder may be inflamed. When the hole is dry, and the charge of powder introduced, the nail, a small taper rod of copper, is inserted so as to reach the bottom of the hole, which is now ready for tamping. By this difficult and dangerous process, the gunpowder is confined, and the disruptive effect produced. Different substances are employed for tamping, or cramming the hole, the most usual one being any soft species of rock free from siliceous or flinty particles. Small quantities of it only are introduced at a time, and rammed very hard by the tamping-bar, which is held steadily by one man, and struck with a sledge by another. The hole being thus filled, the nail is withdrawn by putting a bar through its eye, and striking it upwards. Thus a small perforation or vent is left for the rush which communicates the fire. Besides the improved tamping-bar faced with hard copper, other contrivances have been resorted to for diminishing the risk of those dreadful accidents that frequently occur in this operation. Dry sand is sometimes used as a tamping material, but there are many rocks for the blasting of which it is ineffective. Tough clay will answer better in several situations. For conveying the fire, the large and long green rushes which grow in marshy ground are selected. A slit is made in one side of the rush, along which the sharp end of a bit of stick is drawn, so as to extract the pith, when the skin of the rush closes again by its own elasticity. This tube is filled up with gunpowder, dropped into the vent-hole, and made steady with a bit of clay. A paper smift, adjusted to burn a proper time, is then fixed to the top of the rush-tube, and kindled, when the men of the mine retire to a safe distance. In fig. 709. the portion of the rock which would be dislodged by the explosion, is that included between A and B. The charge of powder is represented by the white part which fills the hole up to C; from which point to the top, the hole is filled with tamping. The smift is shewn at D. Fig. 711. is an iron bucket, or as it is called in Cornwall, a kibble, in which the ore is raised in the shafts, by machines called whims, worked by horses. The best kibbles Fig. 712. represents the wheelbarrow used under ground for conveying ore and waste to the foot of the shafts. It is made of light deal, except the wheel, which has a narrow rim of iron. Fig. 713. represents Mr. Taylor’s ingenious ventilator, or machine for renewing fresh air in mines. It is so simple in construction, so complete in its operation, requires so little power to work it, and is so little liable to injury from wear, that nothing further of the kind can be desired in ordinary metallic mines. The shaft of the mine is represented at A; at either the top or bottom of which the machine may be placed, as is found most convenient, but the foul air must be discharged into a floor, furnished with a valve-door to prevent its return into the mine. B is the air-pipe from the mine, passing through the bottom of the fixed vessel or cylinder C, which is formed of timber, and bound with iron hoops. It is filled with water nearly to the top of the pipe B, on which is fixed a valve opening upwards at D. E, the air, or exhausting cylinder of cast-iron, open at bottom, and suspended over the air-pipe, but immersed some way in the water. It is furnished with a wooden top, having an aperture fitted with a valve likewise opening upwards at F. This exhausting cylinder is moved up and down by the bob G, brought into connexion with any engine by the horizontal rod H; the weight of the cylinder being balanced, if necessary, by the counterpoise I. The action is as follows:—When the cylinder rises, the air from the mine rushes up through the pipe and valve D; and when it descends, this valve shuts, and prevents the return of the air, which is expelled through the valve F. With a cylinder two feet in diameter and six feet long, working from two to three strokes per minute, 200 gallons of air may be discharged in the same time. Gunpowder is the most valuable agent of excavation; possessing a power which has no limit, and which can act every where, even under water. Its introduction, in 1615, caused a great revolution in the mining art. It is employed in mines in different manners, and in different quantities, according to circumstances. In all cases, however, the process resolves itself into boring a hole, and enclosing a cartridge in it, which is afterwards made to explode. The hole is always cylindrical, and is usually made by means of the borer, fig. 704., a stem of iron, terminated by a blunt-edged chisel. It sometimes ends in a cross, formed by two chisels set transversely. The workman holds the stem in his left hand, and strikes it with an iron mallet held in his right. He is careful to turn the punch a very little round at every stroke. Several punches are employed in succession, to bore one hole; the first shorter, the latter ones longer, and somewhat thinner. The rubbish is withdrawn as it accumulates, at the bottom of the hole, by means of a picker, which is a small spoon or disc of iron fixed at the end of a slender iron rod. When holes of a large size are to be The gunpowder, when used, is most commonly put up in paper cartridges. Into the side of the cartridge, a small cylindrical spindle or piercer is pushed. In this state the cartridge is forced down to the bottom of the hole, which is then stuffed, by means of the tamping bar, fig. 708., with bits of dry clay, or friable stones coarsely pounded. As the piercer must not only be slender, but stiff, so as to be easily withdrawn when the hole is tamped, iron spindles are usually employed, though they occasionally give rise to sparks, and consequently to dangerous accidents, by their friction against the sides of the hole. Brass piercers have been sometimes tried; but they twist and break too readily. Each hole bored in a mine, should be so placed in reference to the schistose structure of the rock, and to its natural fissures, as to attack and blow up the least resisting masses. Sometimes the rock is prepared beforehand for splitting in a certain direction, by means of a narrow channel excavated with the small hammer. The quantity of gunpowder should be proportional to the depth of the hole, and the resistance of the rock; and merely sufficient to split it. Anything additional would serve no other purpose than to throw the fragments about the mine, without increasing the useful effect. Into the holes of about an inch and a quarter diameter, and 18 inches deep, only two ounces of gunpowder are put. It appears that the effect of the gunpowder may be augmented by leaving an empty space above, in the middle of, or beneath the cartridge. In the mines of Silesia, the consumption of gunpowder has been eventually reduced, without diminishing the product of the blasts, by mixing sawdust with it in certain proportions. The hole has also been filled up with sand in some cases, according to Mr. Jessop’s plan, instead of being packed with stones, which has removed the danger of the tamping operation. The experiments made in this way have given results very advantageous in quarry blasts with great charges of gunpowder; but less favourable in the small charges employed in mines. Water does not oppose an insurmountable obstacle to the employment of gunpowder; but when the hole cannot be made dry, a cartridge bag impermeable to water must be had recourse to, provided with a tube also impermeable, in which the piercer is placed. After the explosion of each mining charge, wedges and levers are employed, to drag away and break down what has been shattered. Wherever the rock is tolerably hard, the use of gunpowder is more economical and more rapid than any tool-work, and is therefore always preferred. A gallery, for example, a yard and a half high, and a yard wide, the piercing of which by the hammer formerly cost from five to ten pounds sterling, the running yard, in Germany, is executed at the present day by gunpowder at from two to three pounds. When, however, a precious mass of ore is to be detached, when the rock is cavernous, which nearly nullifies the action of gunpowder, or when there is reason to apprehend that the shock caused by the explosion may produce an injurious fall of rubbish, hand-tools alone must be employed. In certain rocks and ores of extreme hardness, the use both of tools and gunpowder becomes very tedious and costly. Examples to this effect are seen, in the mass of quartz mingled with copper pyrites, worked at Rammelsberg, in the Hartz, in the masses of stanniferous granite of Geyer and Altenberg in the Erzgebirge of Saxony, &c. In these circumstances, fortunately very rare, the action of fire is used with advantage to diminish the cohesion of the rocks and the ores. The employment of this agent is not necessarily restricted to these difficult cases. It was formerly applied very often to the working of hard substances; but the introduction of gunpowder into the mining art, and the increase in the price of wood, occasion fire to be little used as an ordinary means of excavation, except in places where the scantiness of the population has The action of fire may be applied to the piercing of a gallery, or to the advancement of a horizontal cut, or to the crumbling down of a mass of ore, by the successive upraising of the roof of a gallery already pierced. In any of these cases, the process consists in forming bonfires, the flame of which is made to play upon the parts to be attacked. All the workmen must be removed from the mine during, and even for some time after, the combustion. When the excavations have become sufficiently cool to allow them to enter, they break down with levers and wedges, or even by means of gunpowder, the masses which have been rent and altered by the fire. To complete our account of the manner in which man may penetrate into the interior of the earth, we must point out the form of the excavations that he should make in it. In mines, three principal species of excavations may be distinguished; viz. shafts, galleries, and the cavities of greater or less magnitude which remain in the room of the old workings. A shaft or pit is a prismatic or cylindrical hollow space, the axis of which is either vertical or much inclined to the horizon. The dimension of the pit, which is never less than 32 inches in its narrowest diameter, amounts sometimes to several yards. Its depth may extend to 1000 feet, and more. Whenever a shaft is opened, means must be provided to extract the rubbish which continually tends to accumulate at its bottom, as well as the waters which may percolate down into it; as also to facilitate the descent and ascent of the workmen. For some time a wheel and axle erected over the mouth of the opening, which serve to elevate one or two buckets of proper dimensions, may be sufficient for most of these purposes. But such a machine becomes ere long inadequate. Horse-whims, or powerful steam-engines, must then be had recourse to; and effectual methods of support must be employed to prevent the sides of the shaft from crumbling and falling down. A Gallery is a prismatic space, the straight or winding axis of which does not usually deviate much from the horizontal line. Two principal species are distinguished; the galleries of elongation, which follow the direction of a bed or a vein; and the transverse galleries, which intersect this direction under an angle not much different from 90°. The most ordinary dimensions of galleries are a yard wide, and two yards high; but many still larger may be seen traversing thick deposits of ore. There are few whose width is less than 24 inches, and height less than 40; such small drifts serve merely as temporary expedients in workings. Some galleries are several leagues in length. We shall describe in the sequel the means which are for the most part necessary to support the roof and the walls. The rubbish is removed by waggons or wheelbarrows of various kinds. See fig. 712. It is impossible to advance the boring of a shaft or gallery beyond a certain rate, because only a limited set of workmen can be made to bear upon it. There are some galleries which have taken more than 30 years to perforate. The only expedient for accelerating the advance of a gallery, is to commence, at several points of the line to be pursued, portions of galleries which may be joined together on their completion. Whether tools or gunpowder be used in making the excavations, they should be so applied as to render the labour as easy and quick as possible, by disengaging the mass out of the rock at two or three of its faces. The effect of gunpowder, wedges, or picks, is then much more powerful. The greater the excavation, the more important is it to observe this rule. With this intent, the working is disposed in the form of steps (gradins), placed like those of a stair; each step being removed in successive portions, the whole of which, except the last, are disengaged on three sides, at the instant of their being attacked. The substances to be mined occur in the bosom of the earth, under the form of alluvial deposits, beds, pipe-veins, or masses, threads or small veins, and rake-veins. When the existence of a deposit of ore is merely suspected, without positive proofs, recourse must be had to labours of research, in order to ascertain the richness, nature, and disposition of a supposed mine. These are divided into three kinds; open workings, subterranean workings, and boring operations. 1. The working by an open trench, has for its object to discover the outcropping or basset edges of strata or veins. It consists in opening a fosse of greater or less width, which, after removing the vegetable mould, the alluvial deposits, and the matters disintegrated by the atmosphere, discloses the native rocks, and enables us to distinguish the beds which are interposed, as well as the veins that traverse them. The trench ought always to be opened in a direction perpendicular to the line of the supposed deposit. This mode of investigation costs little, but it seldom gives much insight. It is chiefly employed for verifying the existence of a supposed bed or vein. The subterranean workings afford much more satisfactory knowledge. They are executed by different kinds of perforations; viz. by longitudinal galleries hollowed out If a vein or bed unveils itself on the flank of a mountain, it may be explored, according to the greater or less slope of its inclination, either by a longitudinal gallery opened in its mass, from the outcropping surface, or by a transverse gallery falling upon it in a certain point, from which either an oblong gallery or a sloping shaft may be opened. If our object be to reconnoitre a highly inclined stratum, or a vein in a level country, we shall obtain it with sufficient precision, by means of shafts, 8 or 10 yards deep, dug at 30 yards distance from one another; excavated in the mass of ore, in the direction of its deposit. If the bed is not very much inclined, only 45°, for example, vertical shafts must be opened in the direction of its roof, or of the superjacent rocky stratum, and galleries must be driven from the points in which they meet the ore, in the line of its direction. When the rocks which cover valuable minerals are not of very great hardness, as happens generally with the coal formation, with pyritous and aluminous slates, sal gem, and some other minerals of the secondary strata, the borer is employed with advantage to ascertain their nature. This mode of investigation is economical, and gives, in such cases, a tolerably exact insight into the riches of the interior. The method of using the borer, has been described under Artesian Wells. OF MINING IN PARTICULAR. The mode of working mines is two-fold; by open excavations, and subterranean. Workings in the open air present few difficulties, and occasion little expense, unless when pushed to a great depth. They are always preferred for working deposits little distant from the surface; where, in fact, other methods cannot be resorted to, if the substance to be raised be covered with incoherent matters. The only rules to be observed are, to arrange the workings in terraces, so as to facilitate the cutting down of the earth; to transport the ores and the rubbish to their destination at the least possible expense; and to guard against the crumbling down of the sides. With the latter view, they ought to have a suitable slope, or to be propped by timbers whenever they are not quite solid. Open workings, are employed for valuable clays, sands, as also for the alluvial soils of diamonds, gold, and oxide of tin, bog iron ores, &c., limestones, gypsums, building stones, roofing slates, masses of rock salt in some situations, and certain deposits of ores, particularly the specular iron of the island of Elba; the masses of stanniferous granite of Geyer, Altenberg, and Seyffen, in the Erzgebirge, a chain of mountains between Saxony and Bohemia; the thick veins or masses of black oxide of iron of Nordmarch, Dannemora, &c., in Sweden; the mass of cupreous pyrites of RÆraas, near Drontheim, in Norway; several mines of iron, copper, and gold in the Ural mountains, &c. Subterranean workings may be conveniently divided into five classes, viz.:— 1. Veins, or beds, much inclined to the horizon, having a thickness of at least two yards. 2. Beds of slight inclination, or nearly horizontal, the power or thickness of which does not exceed two yards. 3. Beds of great thickness, but slightly inclined. 4. Veins, or beds highly inclined, of great thickness. 5. Masses of considerable magnitude in all their dimensions. Subterranean mining requires two very distinct classes of workings; the preparatory, and those for extraction. The preparatory consist in galleries, or in pits and galleries destined to conduct the miner to the point most proper for attacking the deposit of ore, for tracing it all round this point, for preparing chambers of excavation, and for concerting measures with a view to the circulation of air, the discharge of waters, and the transport of the extracted minerals. If the vein or bed in question be placed in a mountain, and if its direction forms a very obtuse angle with the line of the slope, the miner begins by opening in its side, at the lowest possible level, a gallery of elongation, which serves at once to give issue to the waters, to explore the deposit through a considerable extent, and then to follow it in another direction; but to commence the real mining operations, he pierces either shafts or galleries, according to the slope of the deposit, across the first gallery. For a stratum little inclined to the horizon, placed beneath a plain, the first thing is to pierce two vertical shafts, which are usually made to arrive at two points in the same line of slope, and a gallery is driven to unite them. It is, in the first place, for the sake of circulation of air that these two pits are sunk; one of them, which is also destined for the drainage of the waters, should reach the lowest point of the intended workings. With a vein of less than two yards thick, as soon as the preparatory labours have brought the miners to the point of the vein from which the ulterior workings are to ramify, whenever a circulation of air has been secured, and an outlet to the water and the matters mined, the first object is to divide the mass of ore into large parallelopipeds, by means of oblong galleries, pierced 20 or 25 yards below one another, with pits of communication opened up, 30, 40, or 50 yards asunder, which follow the slope of the vein. These galleries and shafts are usually of the same breadth as the vein, unless when it is very narrow, in which case it is requisite to cut out a portion of the roof or the floor. Such workings serve at once the purposes of mining, by affording a portion of ore, and the complete investigation of the nature and riches of the vein, a certain extent of which is thus prepared before removing the cubical masses. It is proper to advance first of all, in this manner, to the greatest distance from the central point which can be mined with economy, and afterwards to remove the parallelopiped blocks, in working back to that point. This latter operation may be carried on in two different ways; of which one consists in attacking the ore from above; and another from below. In either case, the excavations are disposed in steps similar to a stair upon their upper or under side. The first is styled a working in direct or descending steps; and the second a working in reverse, or ascending steps. 1. Suppose, for example, that the post N, fig. 714., included between the horizontal gallery A C, and the shaft A B, is to be excavated by direct steps, a workman stationed upon a scaffold at the point a, which forms the angle between the shaft and the elongated drift, attacks the rock in front of him and beneath his feet. Whenever he has cut out a parallelopiped (a rectangular mass), of from four to six yards broad, and two yards high, a second miner is set to work upon a scaffold at a', two yards beneath the first, who, in like manner, excavates the rock under his feet and before him. As soon as the second miner has removed a post of four or six yards in width, by two in height, a third begins upon a scaffold at a'' to work out a third step. Thus, as many workmen are employed as there are steps to be made between the two oblong horizontal galleries which extend above and below the mass to be excavated; and since they all proceed simultaneously, they continue working in similar positions, in floors, over each other, as upon a stair with very long wide steps. As they advance, the miners construct before them wooden floors c c c c, for the purpose of supporting the rubbish which each workman extracts from his own step. This floor, which should be very solid, serves also for wheeling out his barrow filled with ore. The round billets which support the planks sustain the roof or the wall of the mineral vein or bed under operation. If the rubbish be very considerable, as is commonly the case, the floor planks are lost. However strongly they may be made, as they cannot be repaired, they sooner or later give way under the enormous pressure of the rubbish; and as all the weight is borne by the roof of the oblong gallery underneath, this must be sufficiently timbered. By this ingenious plan, a great many miners may go to work together upon a vein without mutual interference; as the portions which they detach have always two faces at least free, they are consequently more easily separable, either 2. To attack a mass Y, fig. 715., a scaffold m, is erected in one of its terminal pits P P, at the level of the ceiling of the gallery R R', where it terminates below. A miner placed on this scaffold, cuts off at the angle of this mass a parallelopiped 1, from one to two yards high, by six or eight long. When he has advanced thus far, there is placed in the same pit, upon another scaffold m', a second miner, who attacks the vein above the roof of the first cutting, and hews down, above the parallelopiped 1, a parallelopiped of the same dimensions 1', while the first is taking out another 2, in advance of 1. When the second miner has gone forward 6 or 8 yards, a third is placed also in the same pit. He commences the third step, while the first two miners are pushing forwards theirs, and so in succession. In this mode of working, as well as in the preceding, it is requisite to support the rubbish and the walls of the vein. For the first object, a single floor n n n, may be sufficient, constructed above the lower gallery, substantial enough to bear all the rubbish, as well as the miners. In certain cases, an arched roof may be substituted; and in others, several floors are laid at different heights. The sides of the vein are supported by means of pieces of wood fixed between them perpendicularly to their planes. Sometimes, in the middle of the rubbish, small pits are left at regular distances apart, through which the workmen throw the ore coarsely picked, down into the lower gallery. The rubbish occasionally forms a slope f f f, so high that miners placed upon it can work conveniently. When the rich portions are so abundant as to leave too little rubbish to make such a sloping platform, the miners plant themselves upon movable floors, which they carry forward along with the excavations. These two modes of working in the step-form, have peculiar advantages and disadvantages; and each is preferred to the other according to circumstances. In the descending workings or in direct steps, fig. 714., the miner is placed on the very mass or substance of the vein; he works commodiously before him; he is not exposed to the splinters which may fly off from the roof; but by this plan he is obliged to employ a great deal of timber to sustain the rubbish; and the wood is fixed for ever. In the ascending workings, or in reversed steps, fig. 715., the miner is compelled to work in the re-entering angle formed between the roof and the front wall of his excavation, a posture sometimes oppressive; but the weight of the ore conspires with his efforts to make it fall. He employs less timber than in the workings with direct steps. The sorting of the ore is more difficult than in the descending working, because the rich ore is sometimes confounded with the heap of rubbish on which it falls. When seams of diluvium or gravel-mud, occur on one of the sides of the vein, or on both, they render the quarrying of the ore more easy, by affording the means of uncovering the mass to be cut down, upon an additional face. Should the vein be very narrow, it is necessary to remove a portion of the sterile rock which encloses it, in order to give the work a sufficient width to enable the miner to advance. If, in this case, the vein be quite distinct from the rock, the labour may be facilitated, as well as the separation of the ore, by disengaging the vein, on one of its faces through a certain extent, the rock being attacked separately. This operation is called stripping the vein. When it is thus uncovered, a shot of gunpowder is sufficient to detach a great mass of it, unmixed with sterile stones. By the methods now described, only those parallelopipeds are cut out, either in whole or in part, which present indications of richness adequate to yield a prospect of benefit. In other cases, it is enough to follow out the threads of ore which occur, by workings made in their direction. The miner, in searching within the crust of the earth for the riches which it conceals, is exposed to many dangers. The rocks amidst which he digs are seldom or never entire, but are almost always traversed by clefts in various directions, so that impending fragments threaten to fall and crush him at every instant. He is even obliged at times to cut through rotten friable rocks or alluvial loams. Fresh atmospheric air follows him with difficulty in the narrow channels which he lays open before him; and the waters which circulate in the subterranean seams and fissures filter incessantly into his excavation, and tend to fill it. Let us now take a view of the means he employs to escape from these three classes of dangers. 1. Of the timbering of excavations.—The excavations of mines, are divisible into three principal species; shafts, galleries, and chambers. When the width of these excavations is inconsiderable, as is commonly the case with shafts and galleries, their sides can sometimes stand upright of themselves; but more frequently they require to be propped or stayed by billets of wood, or by walls built with bricks or stones; or even by stuffing the space with rubbish. These three kinds of support are called timbering, walling, and filling up. Timbering is most used. It varies in form for the three species of excavations, according to the solidity of the walls which it is destined to sustain. In a gallery, for example, it may be sufficient to support merely the roof, by means of joists placed across, bearing at their two ends in the rock; or the roof and the two walls by means of an upper joist S, fig. 716., which is then called a cap or cornice beam, resting on two lateral upright posts or stanchions, a, b, to which a slight inclination towards each other is given, so that they approach a little at the top, and rest entirely upon the floor. At times, only one of the walls and the roof need support. This case is of frequent occurrence in pipe veins. Pillars are then set up only on one side, and on the other the joists rest in holes of the rock. It may happen that the floor of the gallery shall not be sufficiently firm to afford a sure foundation to the standards; and it may be necessary to make them rest on a horizontal piece called the sole. This is timbering with complete frames. The upright posts are usually set directly on the sole; but the extremities of the cap or ceiling, and the upper ends of the standards, are mortised in such a manner that these cannot come nearer, whereby the cap shall possess its whole force of resistance. In friable and shivery rocks there is put behind these beams, both upon the ceiling and the sides, facing boards, which are planks placed horizontally, or spars of cleft wood, set so close together as to leave no interval. They are called fascines in French. In ordinary ground, the miner puts up these planks in proportion as he goes forwards; but in a loose soil, such as sand or gravel, he must mount them a little in advance. He then drives into the mass behind the wooden frame-work, thick but sharp-pointed planks or stakes, and which, in fact, form the sides of the cavity, which he proceeds to excavate. Their one extremity is thus supported by the earth in which it is thrust, and their other end by the last framing. Whenever the miner gets sufficiently on, he sustains the walls by a new frame. The size of the timber, as well as the distance between the frames or stanchions, depends on the degree of pressure to be resisted. When a gallery is to serve at once for several distinct purposes, a greater height is given to it; and a flooring is laid on it at a certain level. If, for example, a gallery is to be employed, both for the transport of the ores and the discharge of the waters, a floor e e, fig. 715., is constructed above the bottom, over which the carriages are wheeled, and under which the waters are discharged. The timbering of shafts varies in form, as well as that of galleries, according to the nature and the locality of the ground which they traverse, and the purposes which they are meant to serve. The shafts intended to be stayed with timber are usually square or rectangular, because this form, in itself more convenient for the miner, renders the execution of the timbering more easy. The wood-work consists generally of rectangular frames, the spars of which are about eight inches in diameter, and placed at a distance asunder of from a yard to a yard and a half. The spars are never placed in contact, except when the pressure of the earth and the waters is very great. The pieces composing the frames are commonly united by a half-check, and the longer of the two pieces extends often beyond the angles, to be rested in the rock. Whether the shaft is vertical or inclined, the frame-work is always placed so that its plane may be perpendicular to the axis of the pit. It happens sometimes in inclined shafts that there are only two sides, or even a single one, which needs to be propped. These are stayed by means of cross beams, which rest at their two ends in the rock. When the frames In the large rectangular shafts, which serve at once for extracting the ores, for the discharge of the waters, and the descent of the workmen, the spaces destined for these several purposes are in general separated by partitions, which also serve to increase the strength of the timberings, by acting as buttresses to the planks in the long sides of the frame-work. Occasionally a partition separates the ascending from the descending basket, to prevent their jostling.—Lastly, particular passages are left for ventilation. As it is desirable that the wood shall retain its whole force, only those pieces are squared which absolutely require it. The spars of the frames in shafts and galleries are deprived merely of their bark, which by holding moisture, would accelerate the decomposition of the wood. The alburnum of oak is also removed. Resinous woods, like the pine, last much shorter than the oak, the beech, and the cherry-tree; though the larch is used with advantage. The oak has been known to last upwards of 40 years; while the resinous woods decay frequently in 10. The fresher the air in mines, the more durable is the timbering. The marginal figs. 717, 718. represent two vertical sections of a shaft, the one at right angles to the other, with the view of showing the mode of sustaining the walls of the excavation by timbering. It is copied from an actual mine in the Hartz. There we may observe the spaces allotted to the descent of the miners by ladders, to the drainage of the waters by pumps P, and rods t, and to the extraction of the mineral substances by the baskets B. a, b, c, f, h, k, various cross timbers; A, C, E, upright do.; R, pump cistern; V, W, corve-ways. The shafts here shown, are excavated in the line of the vein itself,—the rock enclosing it being seen in the second figure. In a great many mines it is found advantageous to support the excavations by brick or stone buildings, constructed either with or without mortar. These constructions are often more costly than wooden ones, but they last much longer, and need fewer repairs. They are employed instead of timberings, to support the walls and roof of galleries, to line the sides of shafts, and to bear up the roofs of excavations. Sometimes the two sides of a gallery are lined with vertical walls, and its roof is supported by an ogee vault, or an arch. If the sides of the mine are solid, a simple arch is sufficient to sustain the roof and at other times the whole surface of a gallery is formed of a single elliptic vault, the great axis of which is vertical; and the bottom is surmounted by a wooden plank, under which the waters run off; see fig. 719. Walled shafts also are sometimes constructed in a circular or elliptic form, which is better adapted to resist the pressure of the earth and waters. Rectangular shafts of all dimensions, however, are frequently walled. The sides of an excavation may also be supported by filling it completely with rubbish. Wherever the sides need to be supported for some time without the necessity of passing along them, it is often more economical to stuff them up with rubbish, than to keep up their supports. In the territory of Liege, for example, there have been shafts thus filled up for several centuries; and which are found to be quite entire when they are emptied. The rubbish is also useful for forming roads among steep strata, for closing air-holes, and forming canals of ventilation. Figs. 719. 720. 721. represent the principal kinds of mason-work employed in the galleries and shafts of mines. Fig. 722. exhibits the walling in of the cage of an overshot water-wheel, as mounted within a mine. Before beginning to build, an excavation In walling galleries, attention must be paid to the direction of the pressure, and to build vertically or with a slope accordingly. Should the pressure be equal in all directions, a closed vault, like fig. 719., should be formed. For walls not far from the vertical, salient or buttressed arches are employed, as shown in fig. 720., called in German Überspringende bogen; for other cases, twin-arches are preferred, with an upright wall between. Fig. 721. is a transverse section of a walled drain-gallery, from the grand gallery of the Hartz; see also fig. 722. a is the rock which needs to be supported only at the sides and top; b, the masonwork, a curve formed of the three circular arcs upon one level; c, the floor for the watercourse. Fig. 719. is a cross section of a walled gallery, as at Schneeberg, Rothenburg, Idria, &c.; d, is the rock, which is not solid either at the flanks, roof, or floor; e, the elliptic masonwork; f, the wooden floor for the waggons, which is sometimes, however, arched in brick to allow of a watercourse beneath it. Fig. 720. shows two vertical projections of a portion of a walled shaft with buttresses, as built at the mine Vater Abraham, near Marienberg. J is a section in the direction of the vein g h, to show the roof of the shaft. I, a section exhibiting the slope of the vein g h, into which the shaft is sunk; m is the wall of the vein; k is the roof of the same vein; n, buttresses resting upon the flanks of the shaft; g, great arcs on which the buttresses bear; y, vertical masonwork; z, a wall which divides the shaft into two compartments, of which the larger p is that for extracting the ore, and the smaller for the draining and descent of the miners. Fig. 722. C D is the shaft in which the vertical crank-rods c g, e d, move up and down. F, is a double hydraulic wheel, which can be stopped at pleasure by a brake mounted upon the machine of extraction. G, is the drum of the gig or whim for raising the corves or tubs (tonnes); H, is the level of the ground, with the carpentry which supports the whim and its roof. k, is the key-stone of the ogee arch which covers the water-wheel; a, is the opening or window, traversed by the extremity of the driving shaft, upon each side of the water-wheel, through which a workman may enter to adjust or repair it; c b, line of conduits for the streams of water which fall upon the hydraulic Figs. 723. 724. present two vertical sections of the shaft of a mine walled, like the roof of a cavern, communicating with the galleries of the roof and the wall of the vein, and well arranged for both the extraction of the ore, and the descent of the miners. The vertical partition of the shaft for separating the passage for the corves or tubs from the ladders is omitted in the figure, for the sake of clearness. In fig. 723., A, B are the side walls supported upon the buttresses C and D; in fig. 724., E is the masonry of the wall, borne upon the arch F at the entrance to a gallery; the continuation being at G, which is sustained by a similar arch built lower. L, is the vault arch of the roof, supported upon another vault M, which presents a double curvature, at the entrance of a gallery; at H is the continuation of the arch or vault L, which underneath is supported in like manner at the entrance of a lower gallery. a b, c d, fig. 723., are small upright guide-bars or rods for one of the corves, or kibbles. e f, g h, are similar guide-bars for the other corf. i i, are cross-bars of wood, which support the stays of the ladders of descent. k k, are also cross-bars by which the guide-rods are secured. t, a corf, or extraction kibble, furnished with friction rollers; the other corf is supposed to be drawn up to a higher level, in the other vertical passage. Figs. 725. 726. represent in a vertical section the mode of timbering the galleries of the silver and lead mines at Andreasberg in the Hartz. Fig. 725. shows the plan viewed from above. Upon the roof of the timbering, the workman throws the waste rubbish, and in the empty space below, which is shaded black, he transports in his waggons or wheelbarrows the ores towards the mouth of the mine. Fig. 726. is the cross section of the gallery. In the two figures, a represents the rock, and b the timbering; round which there is a garniture of small spars or lathes for the purpose of drainage and ventilation, with the view of promoting the durability of the wood-work. The working of minerals by the mass is well exemplified a few leagues to the north of Siegen, near the village of MÜsen, in a mine of iron and other metals, called Stahlberg, which forms the main wealth of the country. The plan of working is termed the excavation of a direct or transverse mass. It shows in its upper part the danger of bad mining, and in its inferior portion, the regular workings, by whose means art has eventually prevented the destruction of a precious mineral deposit. Fig. 727. is a vertical section of the bed of ore, which is a direct mass of spathose iron, contained in transition rock (greywacke). a, a, a, are pillars of the sparry ore, reserved to support the successive stages or floors, which are numbered 1. 2. 3. &c.; b, b, b, are excavations worked in the ore; which exhibit at the present day several floors of arches, of greater or less magnitude, according to the localities. It may be remarked, that where the metallic deposit forms one entire mass, rich in spathose iron ore of good quality, there is generally given to the vaults a height of three fathoms; leaving a thickness over the roof of two fathoms, on account of the numerous fissures which pervade the mass. But where this mass is divided into three principal branches, the roof of the vaults has only a fathom and a half of thickness, while the excavation is three fathoms and a half high. In the actual state of the workings, it may be estimated that from all this direct mass, there is obtained no more out of every floor than one-third of the mineral. Two-thirds remain as labours of reserve, which may be resumed at some future day, in consequence of the regularity and the continuation of the subterranean workings. e is a shaft for extraction, communicating below with the gallery of efflux k; h is an upper gallery of drainage, which runs in different directions (one only being visible in this section) over a length of 400 fathoms. The lower gallery k runs 646 fathoms in a straight line. The mine of Stahlberg has furnished annually on an average since 1760 about 25,000 cubic feet (French) of an excellent spathose ore of iron. m m, represents the mass of sparry iron. Figs. 728, 729, 730. represent the cross system of mining, which consists in forming galleries through a mineral deposit, from its wall or floor towards its roof, and not, as usual, in the direction of its length. This mode was contrived towards the middle of the 18th century, for working the very thick veins of the Schemnitz mine in Hungary, and it is now employed with advantage in many places, particularly at Idria in Carniola. In the two sections figs. 728., 730., as well as in the ground plan fig. 729., the wall is denoted by m m, and the roof by t t. A first gallery of prolongation E F, fig. 730., being formed to the wall, transverse cuts, a a, are next established at right angles to this gallery, so that between every two there may be room enough to place three others, b, c, b, fig. 729. From each of the cuts a, ore is procured by advancing with the help of timbering, till the roof t be reached. When this is done, these first cuts a, are filled up with rubbish, laid upon pieces of timber with which the ground is covered, so that if eventually, it should be wished to mine underneath, no downfall of detritus is to be feared. These heaps of rubbish rise only to within a few inches of the top of the cuts a, in order that the working of the upper story may be easier, the bed of ore being there already laid open upon its lower face. In proportion as the cuts a, of the first story E F, are thus filled up, the greater part of the timbering is withdrawn, and made use of elsewhere. The intermediate cuts b, c, b, are next mined in like manner, either beginning with the cuts c, or the cuts b, according to the localities. From fig. 729. it appears that the working may be so arranged, that in case of necessity, there may be always between two cuts in activity the The exploration of the upper stories E' F', E2 F2, E3 F3, is now prepared in a similar manner; with which view shafts h h3, k k3, are formed from below upwards in the wall m of the deposit, and from these shafts oblong galleries proceed, established successively on a level with the stories thus raised over one another. See fig. 730. The following objects may be specified in the figures:— a a, the first cuts filled up with rubbish, upon the first story E F, fig. 729. b b, other cuts subsequently filled up, upon the same story. c, the cut actually working. d, the front of the cut, or place of actual excavation of the mineral deposit. e, masses of the barren rock, reserved in the cutting, as pillars of safety. f, galleries, by means of which the workmen may turn round the mass e, in order to form, in the roof t, an excavation in the direction of the deposit. g, rubbish behind the mass e. k k, two shafts leading from the first story E F, to the upper stories of the workings, as already stated. m, the wall, and t the roof of the mineral bed. In the second story E' F', the gallery of prolongation F', figs. 728. and 730., is not entirely perforated; but it is further advanced than that of the third story, which, in its turn, is more than the gallery of the fourth. From this arrangement there is produced upon fig. 730. the general aspect of a working by reversed steps. Whenever the workings of the cuts c in the first story are finished, those of the second, a' a', may be begun in the second; and thus by mounting from story to story, the whole deposit of ore may be taken out and replaced with rubbish. One great advantage of this method is, that nothing is lost; but it is not the only one. The facilities offered by the system of cross workings for disposing of the rubbish, most frequently a nuisance to the miner, and expensive to get rid of, the solidity which it procures by the banking up, the consequent economy of timbering, and saving of expense in the excavation of the rock, reckoning from the second story, are so many important circumstances which recommend this mode of mining. Sometimes, indeed, rubbish may be wanted to fill up, but this may always be procured by a few accessory perforations; it being easy to establish in the vicinity of the workings a vast excavation in the form of a vault, or kind of subterraneous quarry, which may be allowed to fall in with proper precautions, and where rubbish will thus accumulate in a short time, at little cost. Fig. 731. represents a section of the celebrated lead mines of Bleyberg in Carinthia, not far from Villach. b, c, is the ridge of the mountains of compact limestone, in whose bosom the workings are carried on. e, is the metalliferous valley, running from east to west, between the two parallel f g, is the direction of a great many vertical beds of metalliferous limestone. On considering the direction and dip of the marly schist, and metalliferous limestone, in the space w, w, to the west of the line 1, s, it would appear that a great portion of this system of mountains has suffered a slip between 1, s, and a parallel one towards the east; whereby, probably, that vertical position of the strata has been produced, which exists through a considerable extent. The metalliferous limestone is covered to a certain thickness with a marly schist, and other more recent rocks. It is in this schist that the fine marble known under the name of the lumachella of Bleyberg is quarried. The galena occurs in the bosom of this rock in flattened masses, or blocks of a considerable volume, which are not separated from the rest of the calcareous beds by any seam. It is accompanied by zinc ore (calamine), especially in the upper parts of the mountain. Several of the workable masses are indicated by r, r3; each presents itself as a solid analogous to a very elongated ellipse, whose axis dips, not according to the inclination of the surrounding rock, but to an oblique or intermediate line between this inclination, and the direction of the beds of limestone; as shown by r w, r' u. Every thing indicates the contemporaneous formation of the limestone, and the lying beds of the lead ore. The accidents or faults called kluft (rent) at Bleyberg are visible on the surface of the ground. Experienced miners have remarked that the rich masses occur more frequently in the direction of these accidents than elsewhere. It is in general by galleries cut horizontally in the body of the mountain, and at different levels, s, g, s f, that the miner advances towards the masses of ore r, r3. Many of these galleries are 500 fathoms long before they reach a workable mass. The several galleries are placed in communication by a few shafts, such as t; but few of these are sunk deeper than the level of the valley e. The total length of the mines of Bleyberg is about 10,000 yards, parallel to the valley e; in which space there are 500 concessions granted by the government to various individuals or joint stock societies, either by themselves or associated with the government. The metalliferous valley contains 5000 inhabitants, all deriving subsistence from the mines; 300 of whom are occupied in the government works. Each concession has a number and a name; as Antoni, Christoph, MatthÆus, Oswaldi, 2, 8, 36, &c. Fig.. 732 is a section in the quicksilver mine of Idria. 1. is the gray-limestone; 2. is a blackish slate; 5. is a grayish slate. Immediately above these transition rocks lies the bed containing the ores called corallenerz, which consist of an intimate mixture of sulphuret of mercury and argillaceous limestone; in which four men can cut out, in a month, 21/2 toises cube of rock. Fig. 733. represents a section of part of the copper mine of Mansfeldt; containing the cellular limestone, called rauchwacke, always with the compact marl-limestone called zechstein; the cupreous schist, or kupferschiefer; the wall of grayish-white sandstone, called the weisse liegende; and the wall of red sandstone, or the rothe liegende. The thin dotted stratum at top is vegetable mould; the large dotted portion to the right of the figure is oolite; the vein at its side is sand; next is rauchwacke; and lastly, the main body of fetid limestone, or stinkstein. Fig. 734. represents one of the Mansfeldt copper schist mines in the district called Burgoerner, or Preusshoheit. 1. Vegetable mould, with siliceous gravel. 2. Ferruginous clay or loam. 3. Sand, with fragments of quartz. 4. Red clay, a bed of variable thickness as well as the lower strata, according as the cupreous schist is nearer or farther from the surface. 5. Oolite (roogenstein). 6. Newer variegated sandstone, (bunter sandstein). 7. Newer gypsum; below which, there is 8. A bluish marly clay. 9. Stinkstone, or lucullite. 10. Friable grayish marl. 11. Older gypsum, a rock totally wanting in the other districts of the mines of Rothenberg; but abounding in Saxon Mansfeldt, where it includes vast caverns known among the miners by the name of schlotten, as indicated in the figure. 12. The calcareous rock called zechstein. The lower part of this stratum shows symptoms of the cupriferous schist that lies underneath. It presents three thin bands, differently modified, which the miner distinguishes as he descends by the names of the sterile or rotten (faÜle) rock; the roof (dachklotz); and the main rock (oberberg.) 13. Is a bed of cupriferous schist (kupferschiefer), also called the bitumino-marly schist, in which may be noted, in going down, but not marked in the figure:—
These seams are not worth smelting; the following, however, are:—
14. The wall of sandstone, resting upon a porphyry. Fig. 735. is a section of the mines of Kiegelsdorf in Hessia, presenting— 1. Vegetable mould. 2. Limestone distinctly stratified, frequently of a yellowish colour, called lagerhafter kalkstein. 3. Clay, sometimes red, sometimes blue, sometimes a mixture of red, blue, and yellow. 4. The cellular limestone (rauhkalk). This rock differs both in nature and position from the rock of the same name at Mansfeldt. 5. Clay, usually red, containing veins of white gypsum, and fine crystals of selenite. 6. Massive gypsum of recent formation. 7. Fetid limestone, compact and blackish gray, or cellular and yellowish gray. 8. Pulverulent limestone, with solid fragments interspersed. 9. Compact marl-limestone, or zechstein, which changes from a brownish colour above to a blackish schist below, as it comes nearer the cupreous schist, which seems to form a part of it. 10. Cupreous schist (kuperschiefer), of which the bottom portion, from 4 to 6 inches thick, is that selected for metallurgic operations. Beneath it, is found the usual wall or bed of sandstone. A vein of cobalt ore a, which is rich only in the grayish-white sandstone (weisse liegende), traverses and deranges all the beds wherever it comes. Of working mines by fire.—The celebrated mine worked since the tenth century in the mountain called Rammelsberg, in the Hartz, to the south of Goslar, presents a stratified A mine so ancient as that of Rammelsberg, and which was formerly divided among several adventurous companies, cannot fail to present a great many shafts and excavations; but out of the 15 pits, only two are employed for the present workings; namely, those marked A B and E F, in fig. 736., by which the whole extraction and drainage are executed.—The general system of exploitation by fire, as practised in this mine, consists of the following operations:— 1. An advance is made towards the deposits of ore, successively at different levels, by transverse galleries which proceed from the shaft of extraction, and terminate at the wall of the stratiform mass. 2. There is formed in the level to be worked, large vaults in the heart of the ore, by means of fire, as we shall presently describe. 3. The floor of these vaults is raised up by means of terraces formed from the rubbish, in proportion as the roof is scooped out. 4. The ores detached by the fire from their bed, are picked and gathered; sometimes the larger blocks are blasted with gunpowder. 5. Lastly, the ores thus obtained are wheeled towards the shaft of extraction, and turned out to the day. Let us now see how the excavation by fire is practised; and in that view, let us consider the state of the workings in the mines of Rammelsberg in 1809. We may remark in fig. 736. the regularity of the vaults previously scooped out above the level B C, and the other vaults which are in full activity of operation. It is, therefore, towards the lower levels that the new workings must be directed. For this purpose, the transverse gallery being already completed, there is prepared on the first of these floors a vault of exploitation at b, which eventually is to become similar to those of the superior levels. At the same time, there is commenced at the starting point below it, reached by a small well dug in the line of the mineral deposit, a transverse gallery in the rock, by means of blasting with gunpowder. The rock is also attacked at the starting-point by a similar cut, which advances to meet the first perforation. In this way, whenever the vaults of the level C are exhausted of ore and terraced up with rubbish, those of the level beneath it will be in full activity. Others will then be prepared at a lower level; and the exploitation may afterwards be driven below this level by pursuing the same plan, by which the actual depth of excavation has been gained. In workings by fire we must distinguish, 1. The case where it is necessary to open a vault immediately from the floor; 2. The case where the vault having already a certain elevation, it is necessary to heighten its roof. In the former case, the wall or floor of the mineral deposit is first penetrated by blasting with gunpowder. As soon as this penetration is effected over a certain length, parallel to the direction of the future vault, as happens at b, there is arranged on the bottom a horizontal layer of billets of firwood, over which other billets are piled in nearly a vertical position, which rest upon the ore, so that the flame in its expansion comes to play against the mineral mass to be When the vault has already a certain height, care is always taken that between the roof of the vault and the rubbish on which the pile is arranged, no more than two yards of space should intervene, in order that the flame may embrace equally the whole concavity of the vault, and produce an uniform effect on all its parts. Here, the pile is formed of horizontal beds, disposed crosswise above one another, and presents four free vertical faces, whence it has been called a chest by the miners. It is usually on Saturday that the fire is applied to all the piles of faggots distributed through the course of the week. Those in the upper floors of exploitation are first burned, in order that the inferior piles may not obstruct by their vitiated air, the combustion of the former. Thus, at 4 o’clock in the morning, the fires are kindled in the upper ranges; from pile to pile, the fireman and his assistant descend towards the lower floors, which occupies them till 3 o’clock in the afternoon. Vainly should we endeavour to describe the majestic and terrific spectacle which the fire presents, as it unfolds its wings under its metallic vaults, soon filled with vast volumes of smoke and flame. Let us mark the useful effect which it produces. When the flame has beat for a few instants on the beds of ore, a strong odour of sulphur, and sometimes of arsenic is perceived; and soon thereafter loud detonations are heard in the vaults. Suddenly the flame is seen to assume a blue colour, or even a white; and at this period, after a slight explosion, flakes of the ore, of greater or less magnitude, usually fall down on the fire, but the chief portion of the heated mineral still remains fixed to the vault. The ores pass now into a shattered and divided condition, which allows them afterwards to be detached by long forks of iron. In this manner the fire, volatilizing entirely some principles, such as sulphur, zinc, arsenic, and water, changing the aggregation of the constituent parts of the ore, and causing fissures by their unequal expansibilities, facilitates the excavation of such materials as resist by their tenacity the action of gunpowder. The combustion goes on without any person entering the mine from Saturday evening till Monday morning, on which day, the fireman and his assistants proceed to extinguish the remains of the bonfires. On Monday also some piles are constructed in the parts where the effect of the former ones has been incomplete; and they are kindled after the workmen have quitted the mine. On Tuesday all hands are employed in detaching the ores, in sorting them, taking them out, and preparing new piles against the next Saturday. The labour of a week consists for every man of five posts during the day, each of 8 hours, and of one post of four hours for Saturday. Moreover, an extra allowance is made to such workmen as employ themselves some posts during the night. The labour of one compartment or atelier of the mine consists therefore in arranging the faggots, in detaching the ore which has already experienced the action of the fire, in breaking the blocks obtained, in separating the ore from the dÉbris of the pile, and whenever it may be practicable or useful, in boring holes for blasting with gunpowder. The heat is so great in this kind of mine, that the men are obliged to work in it without clothing. We have already remarked, that besides the working by fire, which is chiefly used here, recourse is sometimes had to blasting by gunpowder. This is done in order either to recover the bottom part or ground of the vaults on which the fire can act but imperfectly, to clear away some projections which would interfere with the effect of the pile, or lastly to strip the surrounding rock from the mass of the ore, and thence to obtain schist proper for the construction of the rubbish-terraces. The blasting process is employed when the foremen of the workshop or mine-chamber judge that a hole well placed may separate enough of ore to pay the time, the repair of tools, and the gunpowder expended. But this indemnification is rarely obtained. The following statement will give an idea of the tenacity which the mineral deposit often presents. In 1808, in a portion of the Rammelsberg mine, the ore, consisting of extremely compact iron and copper pyrites, was attacked by a single man, who bored a mining hole. It is therefore evident that though the timber, of which the consumption is prodigiously great, were much less abundant and dearer than it still is at Rammelsberg, mining by fire would be preferable to every other mode of exploitation. It is even certain, that on any supposition, the employment of gunpowder would not be practicable for every part of the mine; and if fuel came to fail, it would be requisite to renounce the workings at Rammelsberg, although this mountain still contains a large quantity of metals. If in all mines the free circulation of air be an object of the highest importance, we must perceive how indispensable it must be in every part of a mine where the mode of exploitation maintains the temperature of the air at 112° Fahr., when the workmen return into it after the combustion of the piles, and in which besides it is necessary that this combustion be effected with activity in their absence. But in consequence of the extent and mutual ramifications of the workings, the number of the shafts, galleries, and their differences of level, the ventilation of the mine is in a manner spontaneously maintained. The high temperature is peculiarly favourable to it. The aid of art consists merely in placing some doors judiciously, which may be opened or shut at pleasure, to carry on the circulation of the air. In considering the Rammelsberg from its summit, which rises about 400 yards above the town of Goslar, we observe, first, beds of slaty sandstone, which become the more horizontal the nearer they approach to the surface. At about 160 yards below the top level there occurs, in the bosom of the slaty graywacke, a powerful stratum of shells impasted in a ferruginous sandstone. See D, fig. 730. In descending towards the face of the ore, the parallel stratification of the clay-slate which forms its walls and roof grows more and more manifest. Here the slate is black, compact, and thinly foliated. The inclination of the different beds of rock is indicated at B. The substance of the workable mass is copper and iron pyrites, along with sulphuret of lead, accompanied by quartz, carbonate of lime, compact sulphate of baryta, and occasionally gray copper (fahlerz), sulphuret of zinc, and arsenical pyrites. The ores are argentiferous and auriferous, but very slightly so, especially as to the gold. It is the ores of lead and copper which contain the silver, and in the latter the gold is found, but without its being well ascertained in what mineral it is deposited. Sometimes the copper occurs in the native state, or as copper of cementation. Beautiful crystals of sulphate of lime are found in the old workings. Fig. 737 enlarged (150 kB) In figs. 736. 737., A B is the shaft of extraction, called the Kahnenkuhler; N is the ventilation shaft, called Breitlingerwetterschacht; P is the extraction shaft, called Innier-schacht. E F, is a new extraction-shaft, called Neuer treibschacht, by which also the water is pumped up; by A B, and E F, the whole extraction and draining are carried on. The ores are raised in these shafts to the level of the waggon-gallery (galerie de roulage) i, by the whims l, q, provided with ropes and buckets. 1, 2, 3, 4, fig. 736., represent the positions of four water-wheels for working the whims; the first two being employed in extracting the ores, the last two in draining. The driving stream is led to the wheel 1, along the drift l; whence it falls in succession upon the wheels 2, 3, 4. The general system of working consists of the following operation;— 1. The bed of ore is got at by the transverse galleries, m, n, o, q, r, s, which branch off from the extraction shaft, and terminate at the wall of the main bed; 2. Great vaults are scooped out at the level of the workings, by means of fire; 3. The roofs of these vaults are progressively propped with mounds of rubbish; 4. The ores thus detached, or by blasting with gunpowder, are then collected; 5. Lastly, they are wheeled out to the day; and washed near Z. Comparative Table of celebrated Mines in Europe and America. By F. Burr, Esq.
VENTILATION OF MINES. When men penetrate by narrow passages into the interior of the earth, their respiration, joined to the combustion of candle and gunpowder, are not long of vitiating the air. The decomposition of wood contributes to the same effect, as also the mineral bed itself, especially in coal mines, by the carburetted hydrogen and carbonic acid evolved, and from the absorption of oxygen by pyrites. In many cases, arsenical and mercurial vapours are disengaged. Hence the necessity of maintaining in subterranean These means are divided into natural and artificial. The natural means are the currents produced by the difference of density between the air of mines and the external air; the artificial are air-exhausters or condensers, fires, &c. The temperature of the air of the subterranean workings surpasses the mean temperature of the place in which the mine is opened. Hence it is lighter in winter, but in summer often heavier than the air of the atmosphere. For this reason, when the mine presents two openings at different levels, the air naturally flows out by the most elevated in winter, and by the lowest in summer. We may take advantage of this circumstance, to lead the air into the bottom of even a very long gallery, opening into the side of the mountain, by piercing a shaft into its roof at some distance from the entrance, and dividing the gallery by a horizontal floor into two parts, which have no mutual communication, except at the furthest extremity—the upper part communicating with the shaft, and the under with the mouth of the gallery. If the two compartments have different dimensions, the air in the smaller sooner comes into an equilibrium of temperature with the rock; and the difference of temperature of the two compartments is sufficient to produce a current. If a streamlet of water flows through this gallery, it facilitates the flow of the air along the lower compartment. If a mine has several openings situated on the same level, it rarely happens but some peculiar circumstance destroys, during the colds of winter and the heats of summer, the equilibrium of the air. But in spring and autumn, when the external air is nearly of the same temperature with that of the mines, the above-named causes are almost always too feeble to excite an issuing current. This effect is, however, frequently obtained by raising over one of the shafts a chimney 20 or 30 yards high, which alone produces the effect of an opening at a different level. It has been remarked that stormy weather usually deranges every system of ventilation. See Pitcoal and Ventilation. The best minium, however, called orange mine, is made by the slow calcination of good white lead (carbonate) in iron trays. If the lead contains either iron or copper, it affords a minium which cannot be employed with advantage in the manufacture of flint-glass, for pottery glazes, or for house-painting. Dumas found several samples of red lead which he examined to consist of the chemical sesquioxide and the protoxide, in proportions varying from 50 of the former and 50 of the latter, to 95·3 of the former and 4·7 of the latter. The more oxygen gas it gives out when heated, the better it is, generally speaking. See Naples Yellow. The inconvenience of using ingots in general trade, on account of the difficulty of defining fractional values, has determined governments to coin pieces of money, that is, quantities of metal whose weight and standard were made known and guaranteed by the effigies of the prince. It is true, indeed, that kings have become frequently coiners But since knowledge has become more generally diffused, it has been shown that these frauds are equally injurious to the prince and to public faith. A sovereign may, it is true, declare by a decree that a shilling-piece is to be held worth five; but let us consider the consequences of this decree. All the individuals who have rents or capital sums to receive, will be ruined, by getting in metallic value only one-fifth of what is due to them; for although the nominal value should be the same as what they are entitled to, the intrinsic value would be but a fifth of the former; so that when they go to purchase the necessaries or comforts of life, the dealer who sells them will at once raise their price five-fold. Each article of merchandise would thus acquire a nominal price 5 times greater; and he who had received payment of a debt in that money, could not with it procure more than one-fifth of the goods he could have previously commanded. That fraudulent law would, therefore, favour the debtors at the expense of the creditors; and as the state is commonly a great debtor, especially when it has recourse to the depreciation of the currency, it is obvious, that however illicit the gain which it makes, it still does gain; and this is the reason why princes have so often tampered with the mint. But let us examine the other consequences of this decree. If the sovereign is a debtor, he is also a creditor and consumer, and even the most considerable of any. The taxes which he imposes are paid him in this deteriorated money, returned to him at its nominal value; and the purveyors of his armies, his buildings, and his household, sell him their commodities only at the actual market price. We may infer from this simple development that the coin with which he pays for any object has the same intrinsic value as the object; and that the name given to the coin is of no consequence. The prince may call it a crown, a ducat, or a rix-dollar at his pleasure; and he may assign any value to it that his caprice may suggest, yet this will not affect its value; for this is fixed beyond his control by the general nature of things. The prince may, indeed, at the outset, have profited by defrauding his creditors, and by authorizing each debtor to imitate him, but he will soon lose whatever he may have gained; and he will thus learn to his cost that it was bad policy to sacrifice his character by giving an example of a fraud so truly unprofitable in the issue. Moreover, he will lose still as much in the following years, because his treasury will receive only one-fifth part of the taxes, unless he has quintupled the imposts. It may be said, indeed, that he might do the one thing along with the other. But every one knows that this power is neither generally permitted to princes, nor if it were, could it be safely exercised. Serious political crises would combine to endanger the stability of the government; which besides, as the main consumer in the nation, must lose always as much as it seems to gain. It is therefore manifest that the alteration of the standard and weight of the coinage is at once a crime and a ruinous action for the sovereign power to commit; and hence such disastrous measures have been long abandoned in all well-regulated states. A gold sovereign is intrinsically worth 20 shillings minus the cost of coinage; for were it worth more, all our sovereign pieces would be exported or melted down, to obtain the difference of value, however trifling it might be; and were it worth less, it would be the source of loss similar to what the state occasions when it depreciates the coin. To comprehend the true value of a coin, we must regard this piece as an article of merchandise, whose value depends, as that of every thing else, on its usefulness, the esteem in which it is held, and the demand for it in the market. Grain increases in value when there are few sellers and many buyers; gold and silver are in the same predicament. The value of these metals is much augmented, indeed, by the universal currency they obtain when struck into money; a value additional to what they possess as objects of the arts. This value of the precious metals changes with time and place, like that of every merchandise; their abundance, since the discovery of America, has greatly lowered their value; that is, with the same weight of metal, we cannot at the present day purchase the same quantity of corn, land, wool, &c. as formerly. In the countries where silver abounds, this metal has less value, or, in other terms, commodities are dearer. Hence the metal tends to resume its equilibrium in flowing into those places where it is rarer; which means, that the consumer prefers purchasing his commodities there rather than in another place, if he can easily transport them to where they are dearer. It was formerly believed that a country is rich when it has a great deal of gold and silver; but this popular illusion has passed away. Spain has never been poorer than since the discovery of America, because its national industry has been ruined, and the With regard to the relative value of gold and silver, several details have already been given in our view of the mineral wealth of the globe. Three centuries ago, an ounce of gold was worth at London or Paris 10 ounces of silver; now it may be exchanged for 15 ounces and a half. The par of two coins results from the comparison of their weight and standard fineness. Let us take for an example the conversion of English gold sovereigns worth 20 shillings or a pound sterling, in relation to the French louis of 20 francs. The standard of the sovereign gold is 0·917, fine gold being 1000; its weight is 125·256 gr. English, or 7·980855 grammes; by multiplying this weight into its standard, we have a product of 7·318444035; this is, in grammes, the quantity of pure gold contained in the sovereign piece. The piece of 20 francs has a legal standard of 0·9; and multiplying this number by the weight of the louis, 6·45161 grammes, we find that it contains 5·806449 of pure metal. We then make this proportion:— As 5·806449 : 20 francs ? 7·31844 : 25·2079 francs; or the value of the English sovereign is nearly 25·21 francs, in French gold coin. A similar calculation may be made for silver coins. The French rule for finding the par of a foreign gold coin, or its intrinsic value in francs, is to multiply its weight by its standard or titre, and that product by 34/9. The par of foreign silver money, or its intrinsic value in francs, is obtained by multiplying its weight in grammes by its standard in thousand parts, and by 2/9. The French 5-franc piece has its standard or titre at 0·9, and weighs 25 grammes. The assaying of gold for coin and trinkets requires very delicate management. The French take half a gramme at most (about 71/2 grains) of gold, and fuse it with thrice its weight of silver, as already described under Assay. The parting is the next operation. For this purpose the button of gold and silver alloy is first hammered flat on a piece of steel, and then made feebly red hot in burning charcoal or over a lamp flame. After being thus annealed, the metal is passed through the rolling press, till it be converted into a plate about 1/70 of an inch thick. After annealing this riband, it is coiled into a spiral form, introduced immediately into a small matrass of a pear shape, an assay matrass, and about 500 grains of nitric acid, sp. grav. 1·185, are poured over it. Heat being now applied to the vessel, the solution of the silver and copper alloys ensues, and after 22 minutes of constant ebullition, the liquid is poured off and replaced by an equal quantity of nitric acid, likewise very pure, but of the density 1·28. This is made to boil for about 10 minutes, and is then poured off, when the matrass is filled up with distilled water to the brim. In conclusion, a small annealing crucible is inverted as a cup over the mouth of the matrass, which is now turned upside down with a steady hand; the slip of metal falls into the crucible through the water; which by sustaining a part of its weight, softens its descent and prevents its tearing. The matrass is then dexterously removed, without letting its water overflow the crucible. The water is gently decanted from the crucible, which is next covered, placed in the middle of burning charcoal, and withdrawn whenever it becomes red hot. After cooling, the metal slip is weighed very exactly, whence the weight of fine gold in the alloy is known. Stronger acid than that prescribed above would be apt to tear the metallic riband to pieces, and it would be difficult to gather the fine particles of gold together again. The metallic plate becomes at last merely a golden sieve, with very little cohesion. When copper is to be separated from gold by cupellation, a higher temperature is requisite than in cupelling silver coin. The coining apparatus of the Royal Mint of London is justly esteemed a masterpiece of mechanical skill and workmanship. It was erected in 1811, under the direction of the inventor, Mr. Boulton; and has since been kept in almost constant employment. The melting pots (fig. 738.) are made of cast iron, and hold conveniently 400 pounds of metal. They are furnished with a spout or lip for pouring out the metal, and with two ears, on which the tongs of the crane lay hold in lifting them out of the furnace. The pot rests on pedestals on the grate of the furnace, and has a ring cast on its edge to prevent the fuel falling into it. Whenever it becomes red hot, the metal properly prepared and mixed, so as to produce an alloy containing 0·915 parts of gold, is put in, and during the melting, which occupies some hours, it is occasionally stirred. The moulds are meanwhile prepared by warming them in a stove, and thereafter by rubbing their The pot of fused metal is lifted out of the furnace by the crane (fig. 740.), then swung round, and lowered down into the cradle l, m, n, o of the pouring machine, until the ring on the edge of it rests on the iron hoop n, which, being screwed tight up, holds it secure, and the crane-tongs are removed. One of the assistants now takes the winch handle s in one hand, and y in the other. By turning y he moves the carriage forward, so as to bring the first mould beneath the lip of the melting pot; and by turning s, he inclines the pot, and pours the metal into the mould. He then fills the other moulds in succession. The first portion of liquid metal is received in a small iron spoon, and is reserved for the assay-master; a second sample is taken from the centre of the pot, and a third from the bottom part. Each of these is examined as to its quality. Fig. 741., where A represents a large spur wheel, fixed on the extremity of a long The rolling mill contains four pairs of rollers, each driven by its train of wheel work; the mill, therefore, consists of two such sets of wheels and rollers as are represented in our figure. The two shafts are situated parallel to each other, and receive their motion from the same steam engine. This admirable rolling mill was erected by John Rennie, Esq. The ingots are heated to redness in a furnace before they are rolled. The two furnaces for this purpose are situated before two pairs of rollers, which, from being used to consolidate the metal by rolling whilst hot, are termed breaking-down rollers. Two men are employed in this operation; one taking the metal from the furnace with a pair of tongs, introduces it between the rollers; and the other, catching it as it comes through, lifts it over the top roller, and returns it to his fellow, who puts it through again, having previously approximated the rollers a little by their adjusting screws. After having been rolled in this manner four or five times, they are reduced to nearly two-tenths of an inch thick, and increased lengthwise to about four times the breadth of the ingot. These plates, while still warm, are rubbed over with a dilute acid or pickle, to remove the colour produced by the heat, and are then cut up into narrow slips across the breadth of the plate, by means of the circular shears fig. 742. This machine is worked by a spur-wheel at the extremity of the main shaft B of the rolling mill (fig. 741.) It consists of a framing of iron A A, supporting two shafts B B, which are parallel to each other, and move together by means of two equal spur-wheels C C, the lower one of which works with the teeth of the great wheel above mentioned, upon the main shaft of the rolling mill. At the extremities of the two shafts, wheels or circular cutters are fixed with their edges overlapping each other a little way. F represents a shelf on which the plate is laid, and advanced forward to present it to the cutter; and G is a ledge or guide, screwed down on it, to conduct the metal and to regulate the breadth of the piece to be cut off. Hence the screws which fasten down the ledge are fitted in oblong holes, which admit of adjustment. The workman holds the plate flat upon the surface F, and pushing it towards the shears, they will lay hold of it, and draw it through until they have cut the whole length. The divided parts are also prevented from curling up into scrolls, as they do when cut by a common pair of shears; because small shoulders on E and D, behind the cutting edge, keep them straight. Behind the standard, supporting the back pivots of the shafts B B of the cutter, is a frame l, with a screw m tapped through it. This is used to draw the axis of the upper cutter D endwise, and keep its edge in close contact with the edge of the other cutter E. The slips or ribands of plate are now carried to the other two pairs of rollers in the rolling mill, which are made of case-hardened iron, and better polished than the breaking-down rollers. The plates are passed cold between these, to bring them to exactly the same thickness; whence they are called adjusting or planishing rollers. The workman here tries every piece by a common gauge, as it comes through. This is a piece of steel having a notch in it; the inside lines of which are very straight, and inclined to one another at a very acute angle. They are divided by fine lines, so that the edge of the plate being pressed into the notch, will have its thickness truly determined by the depth to which it enters, the divisions showing the thickness in fractions of an inch. In rolling the plate the second time, all the plates are successively passed through the rollers; then the rollers being adjusted, they are passed through another time. This is repeated thrice or even four times; after which they are all tried by the gauge, and A great improvement has been made on that mode of lamination, by the late Mr. Barton’s machine for equalizing the thickness of slips of metal for making coin, which has been for several years introduced into the British mint. A side elevation is shown in fig. 743., and a plan in fig. 744. It operates in the same way as wire-drawing mechanisms; namely, pulls the slips of metal forcibly through an oblong opening, left between two surfaces of hardened steel. The box or case which contains the steel dies, composed of two hardened cylinders, is represented at C in fig. 743. The pincers employed to hold the metal, and draw it through, are shown at s r. The slips of metal to be operated on by the drawing machine, are first rendered thinner at one end, that they may be introduced between the dies, and also between the jaws of the pincers. This thinning of the ends is effected by another machine, consisting of a small pair of rollers, mounted in an iron frame, similar to a rolling-mill. The upper roller is cylindrical, but the lower is formed with 3 flat sides, leaving merely portions of the cylinder entire, between these flat sides. The distance between the centres of the rollers is regulated by screws, furnished with wheels on their upper ends, similar to what is seen in the drawing dies at C. The two rollers have pinions on their axes, which make them revolve together; they are set in motion by an endless strap passing round a drum, upon whose axis is a pinion working into the teeth of a wheel fixed upon the axis of the lower roller. The end of a slip of metal is presented between the rollers while they are in motion, not on that side of the roller which would operate to draw in the slip between them, as in the rolling-press above described, but on the contrary side, so that when one of the flat sides of the under roller fronts horizontally the circumference of the upper roller, an opening is formed, through which the slip of metal is to be inserted until it bears against a fixed stop at the back of the rollers. As the rollers continue to turn round, the cylindrical portions come opposite to each other, and press the metal between them, forcing it outwards, and rendering the part which has been introduced between the rollers as thin as the space between their cylindrical surfaces. Thus the end of the slip of metal becomes attenuated enough to pass between the dies of the drawing machine, and to be seized by the pincers. In using the drawing machine, a boy takes hold of the handle s of the pincers, their hook of connexion with the endless chain l, l, not shown in the present figure, being disengaged, and he moves them upon their wheels towards the die-box C. In this movement the jaws of the pincers get opened, and they are pushed up so close to the The cutting-out machine is exhibited in fig. 745. A A is a basement of stone to support an iron plate B B, on which stand the columns C C, that bear the upper part D of the frame. The iron frame of the machine E, F, E, is fixed down upon the iron plate B, B. The punch d is fixed in the lower part of the inner frame, and is moved up and down by the screw a, which is worked by wipers turned by a steam engine, impelling the lever H, and turning backwards and forwards the axis G, through a sufficient space for cutting the thickness of the metallic lamina. A boy manages this machine. There are twelve of them mounted on the same basement frame in a circular range contained in an elegant room, lighted from the roof. The whole are moved by a steam engine of 16-horse power. The blanks or planchets thus cut out, were formerly adjusted by filing the edges, to bring them to the exact weight; a step which Mr. Barton’s ingenious mechanism has rendered in a great measure unnecessary. The edge is then milled, by a process which Mr. Boulton desires to keep secret, and which is therefore not shown in our mint. But the French mint employs a very elegant machine for the purpose of lettering or milling the edges, called the cordon des monnaies, invented by M. Gengembre, which has entirely superseded the older milling machine of M. Castaing, described in the Encyclopedias. The Napoleon coins of France bear on the edge, in sunk letters, the legend, Dieu protÈge la France; and those of the king, Domine salvum fac regem. This is marked before striking the blank or flan. One machine imprints this legend, and its service is so prompt and easy, that a single man marks in a day 20,000 pieces of 5 francs, or 100,000 francs. Each of the two arc dies E, D, (fig. 746.) carries one half of the legend, engraved in relief on the curved face; these arcs are pieces of steel tempered very hard, and fixed with two screws, one immoveably at E, on the sill which bears the apparatus; the other at D, at the extremity of the lever P, D, which turns round the axis C. The letters of these demi-legends are exactly parallel, and inscribed in an inverse order on the dies. An alternating circular motion is communicated to the handle P. The curvatures of the two dies are arcs of circles described from the centre C; and the interval which separates them, or the difference of the radii, is precisely the diameter of the piece to be milled. As the centre C sustains the whole strain of the milling, and produces, of consequence, a hard friction, this axis must possess a considerable size. It is composed of a squat At a is a vertical tube, containing a pile of blanks for milling. It is kept constantly full; the tube being open at both ends, a little elevated above the circular space a, K, b, which separates the dies, and fixed by a tail m with a screw to the motionless piece A, B. The branch I, c, movable with the piece P, D, passes under the tube, and pushes before it the blank at the bottom of the column, which is received into a small excavation in the form of a circular step, and carried forwards. Matters are thus so arranged as to regulate the issue of the blanks, one by one, on the small step, called the posoir (bed.) As soon as the blank is pushed forwards into contact with the lower edge of the engraved grooves, it is seized by them, and carried on by the strain of milling, without exposing the upper or under surfaces of the blank to any action which may obstruct the printing on its edge. The blank is observed to revolve between the two dies according as the lever P completes its course, and this blank passing from a to K, then to b, meets a circular aperture b, through which it falls into a drawer placed under the sill. The range of the movable lever P is regulated by four pieces, F, F, F, F, solidly sunk in the plate N, N, which bears the whole apparatus. A stud placed on this lever towards D, makes the arm of the posoir I c retire no farther than is necessary for the little blank to issue from the column; and a spring fixed to the centre c, and supported on a peg, brings back the posoir; so that when a screw I comes to strike against the column, the posoir stops, and the movable die D, which continues its progress, finds the blank in a fit position for pressing, seizing, and carrying it on, by reaction of the fixed die E. Thus the edge of the blank is lettered in half a second. A hundred may easily be marked in about three minutes. The coining press is the most beautiful part of the whole mechanism in the British mint; but the limits of this volume will not allow of its being figured upon an adequate scale. An engraving of it may be seen in the Encyclopedia Britannica. The only attention which this noble machine requires is that of a little boy, who stands in a sunk place before the press, and always keeps the tube full of blanks. He has two strings, one of which, when pulled, will put the press in motion by the concealed mechanism in the apartment above; and the other string, when snatched, stops the press. This coining operation goes on at the rate of 60 or 70 strokes per minute; and with very few interruptions during the whole day. The press-room at the Royal Mint contains eight machines, all supported on the same stone base; and the iron beams between the columns serve equally for the presses on each side. The whole has therefore a magnificent appearance. The eight presses will strike more than 19,000 coins in an hour, with only a child to supply each. The grand improvement in these presses, consists; 1. in the precision with which they operate to strike every coin with equal force, which could not be ensured by the old press impelled by manual labour; 2. The rising collar or steel ring in which they are struck, keeps them all of one size, and makes a fair edge, which was not the case with the old coins, as they were often rounded and defaced by the expansion of the metal under the blow; 3. The twisting motion of the upper die is thought to produce a better surface on the flat parts of the coin; but this is somewhat doubtful; 4. The feeding mechanism is very complete, and enables the machine to work much quicker than the old press did, where the workman, being in constant danger of having his fingers caught, was obliged to proceed cautiously, as well as to place the coin true on the die, which was seldom perfectly done. The feeding mechanism of the above press is a French invention; but Mr. Boulton is supposed to have improved upon it. The protoxide consists of 85·69 of metal, and 14·31 of oxygen; the deutoxide consists of 75 of metal, and 25 of oxygen; and the peroxide, or molybdic acid, of 66·6 of metal, and 33·4 of oxygen. These substances are too rare at present to be used in any manufacture. Such is the result with insoluble colouring matters; but for those which are soluble it should be quite the reverse, since they do not possess an affinity for the organic fibres which can counterbalance their affinity for water. In such circumstances, the dyer must have recourse to intermediate bodies, which add their affinity for the colouring matter to that possessed by the particles of the stuff, and increase by this twofold action the intimacy and the stability of the combination. These intermediate bodies are the true mordants. Mordants are in general found among the metallic bases or oxides; whence they might be supposed to be very numerous, like the metals; but as they must unite the twofold condition of possessing a strong affinity for both the colouring matter and the organic fibre, and as the insoluble bases are almost the only ones fit to form insoluble combinations, we may thus perceive that their number may be very limited. It is well known, that although lime and magnesia, for example, have a considerable affinity for colouring particles, and form insoluble compounds with them, yet they cannot be employed as mordants, because they possess no affinity for the textile fibres. Experience has proved, that of all the bases, those which succeed best as mordants are alumina, tin, and oxide of iron; the first two of which, being naturally white, are the only ones which can be employed for preserving to the colour its original tint, at least In order that a combination may result between two bodies, they must not only be in contact, but they must be reduced to their ultimate molecules. The mordants that are to be united with stuffs are, as we have seen, insoluble of themselves, for which reason their particles must be divided by solution in an appropriate vehicle. Now this solvent or menstruum will exert in its own favour an affinity for the mordant, which will prove to that extent an obstacle to its attraction for the stuff. Hence we must select such solvents as have a weaker affinity for the mordants than the mordants have for the stuffs. Of all the acids which can be employed to dissolve alumina, for example, vinegar is the one which will retain it with least energy, for which reason the acetate of alumina is now generally substituted for alum, because the acetic acid gives up the alumina with such readiness, that mere elevation of temperature is sufficient to effect the separation of these two substances. Before this substitution of the acetate, alum alone was employed; but without knowing the true reason, all the French dyers preferred the alum of Rome, simply regarding it to be the purest; it is only within these few years that they have understood the real grounds of this preference. This alum has not, in fact, the same composition as the alums of France, England, and Germany, but it consists chiefly of cubic alum having a larger proportion of base. Now this extra portion of base is held by the sulphuric acid more feebly than the rest, and hence is more readily detached in the form of a mordant. Nay, when a solution of cubic alum is heated, this redundant alumina falls down in the state of a subsulphate, long before it reaches the boiling point. This difference had not, however, been recognised, because Roman alum, being usually soiled with ochre on the surface, gives a turbid solution, whereby the precipitate of subsulphate of alumina escaped observation. When the liquid was filtered, and crystallized afresh, common octahedral alum alone was obtained; whence it was most erroneously concluded, that the preference given to Roman alum was unjustifiable, and that its only superiority was in being freer from iron. Here a remarkable anecdote illustrates the necessity of extreme caution, before we venture to condemn from theory a practice found to be useful in the arts, or set about changing it. When the French were masters in Rome, one of their ablest chemists was sent thither to inspect the different manufactures, and to place them upon a level with the state of chemical knowledge. One of the fabrics, which seemed to him furthest behindhand, was precisely that of alum, and he was particularly hostile to the construction of the furnaces, in which vast boilers received heat merely at their bottoms, and could not be made to boil. He strenuously advised them to be new modelled upon a plan of his own; but, notwithstanding his advice, which was no doubt very scientific, the old routine kept its ground, supported by utility and reputation, and very fortunately, too, for the manufacture; for had the higher heat been given to the boilers, no more genuine cubical alum would have been made, since it is decomposed at a temperature of about 120° F., and common octahedral alum would alone have been produced. The addition of a little alkali to common alum brings it into the same basic state as the alum of Rome. The two principal conditions, namely, extreme tenuity of particles, and liberty of action, being found in a mordant, its operation is certain. But as the combination to be effected is merely the result of a play of affinity between the solvent and the stuff to be dyed, a sort of partition must take place, proportioned to the mass of the solvent, as well as to its attractive force. Hence the stuff will retain more of the mordant when its solution is more concentrated, that is, when the base diffused through it is not so much protected by a large mass of menstruum; a fact applied to very valuable uses by the practical man. On impregnating in calico printing, for example, different spots of the same web with the same mordant in different degrees of concentration, there is obtained in the dye-bath a depth of colour upon these spots intense in proportion to the strength of their various mordants. Thus, with solution of acetate of alumina in different grades of density, and with madder, every shade can be produced, from the fullest red to the lightest pink; and, with acetate of iron and madder, every shade from black to pale violet. We hereby perceive that recourse must indispensably be had to mordants at different stages of concentration; a circumstance readily realized by varying the proportions of the watery vehicle. See Calico-printing and Madder. When these mordants are to be topically applied, to produce partial dyes upon cloth, they must be thickened with starch or gum, to prevent their spreading, and to permit a sufficient body of them to become attached to the stuff. Starch answers best for the more neutral mordants, and If the mordant applied to the surface of the cloth were completely decomposed, and the whole of its base brought into chemical union with it, a mere rinsing or scouring in water would suffice for removing the viscid substances added to it, but this never happens, whatsoever precautions may be taken; one portion of the mordant remains untouched, and besides, one part of the base of the portion decomposed does not enter into combination with the stuff, but continues loose and superfluous. All these particles, therefore, must be removed without causing any injury to the dyes. If in this predicament the stuff were merely immersed in water, the free portion of the mordant would dissolve, and would combine indiscriminately with all the parts of the cloth not mordanted, and which should be carefully protected from such combination, as well as the action of the dye. We must therefore add to the scouring water some substance that is capable of seizing the mordant as soon as it is separated from the cloth, and of forming with it an insoluble compound; by which means we shall withdraw it from the sphere of action, and prevent its affecting the rest of the stuff, or interfering with the other dyes. This result is obtained by the addition of cow-dung to the scouring bath; a substance which contains a sufficiently great proportion of soluble animal matters, and of colouring particles, for absorbing the aluminous and ferruginous salts. The heat given to the dung-bath accelerates this combination, and determines an insoluble and perfectly inert coagulum. Thus the dung-bath produces at once the solution of the thickening paste; a more intimate union between the alumina or iron and the stuff, in proportion to its elevation of temperature, which promotes that union; an effectual subtraction of the undecomposed and superfluous part of the mordant, and perhaps a commencement of mechanical separation of the particles of alumina, which are merely dispersed among the fibres; a separation, however, which can be completed only by the proper scouring, which is done by the dash-wheel with such agitation and pressure (see Bleaching and Dunging) as vastly facilitate the expulsion of foreign particles. See also Bran. Before concluding this article, we may say a word or two about astringents, and especially gall-nuts, which have been ranked by some writers among mordants. It is rather difficult to account for the part which they play. Of course we do not allude to their operation in the black dye, where they give the well known purple-black colour with salts of iron; but to the circumstance of their employment for madder dyes, and especially the Adrianople red. All that seems to be clearly established is, that the astringent principle or tannin, whose peculiar nature in this respect is unknown, combines like mordants with the stuffs and the colouring substance, so as to fix it; but as this tannin has itself a brown tint, it will not suit for white grounds, though it answers quite well for pink grounds. When white spots are desired upon a cloth prepared with oil and galls, they are produced by an oxygenous discharge, effected either through chlorine or chromic acid. The best medium for sticking gold and silver leaf to wood, is the following, called mixtion by the French artists:—1 pound of amber is to be fused, with 4 ounces of mastic in tears, and 1 ounce of Jewish pitch, and the whole dissolved in 1 pound of linseed oil rendered drying by litharge. Painters in distemper sometimes increase the effect of their work, by patches of gold leaf, which they place in favourable positions; they employ the above mordant. The manufacturers of paper hangings of the finer kinds attach gold and silver leaf to them by the same varnish. These crystals, which contain 6·32 per cent. of combined water, are transparent, colourless, four-sided prisms, without smell, and nearly void of taste, fusible at a moderate heat, and then concrete into a radiated translucent mass, but at a higher temperature they grow purple-red. Morphia consists of 72·34 of carbon; 6·366 of hydrogen; 5 of azote; and 16·3 of oxygen. It burns with a red and very smoky flame, is stained red by nitric acid, is soluble in 30 parts of boiling anhydrous alcohol, in 500 parts of boiling water, but hardly if at all in cold water, and is insoluble in ether and oils. The solutions have a strong bitter taste, and an alkaline reaction upon litmus paper. The saline compounds have a bitter taste, are mostly crystallizable, are soluble in water and alcohol (but not in ether), and give a blue colour to the peroxide salts of iron. It is a very poisonous substance. Acetate of morphia is sometimes prescribed, instead of opium, in medicine. The following analyses of different hydraulic limestones, by Berthier, merit confidence:—
No. 1. is from the fresh-water lime formation of ChÂteau-Landon, near Nemours; No. 2. the large-grained limestone of Paris; both of these afford a fat lime when burnt. Dolomite affords a pretty fat lime, though it contains 42 per cent. of carbonate of magnesia; No. 3. is a limestone from the neighbourhood of Paris, which yields a poor lime, possessing no hydraulic property; No. 4. is the secondary limestone of Metz; No. 5. is the lime marl of Senonches, near Dreux; both the latter have the property of hardening under water, particularly the last, which is much used at Paris on this account. All good hydraulic mortars must contain alumina and silica; the oxides of iron and manganese, at one time considered essential, are rather prejudicial ingredients. By adding silica and alumina, or merely the former, in certain circumstances, to fat lime, a water-cement may be artificially formed; as also by adding to lime any of the following native productions, which contain silicates; puzzolana, trass or tarras, pumice-stone, basalt-tuff, slate-clay. Puzzolana is a volcanic product, which forms hills of considerable extent to the south-west of the Appenines, in the district of Rome, the Pontine marshes, Viterbo, Bolsena, and in the Neapolitan region of Puzzuoli, whence the name. A similar volcanic tufa is found in many other parts of the world. According to Berthier, the Italian puzzolana consists of 44·5 silica; 15·0 alumina; 8·8 lime; 4·7 magnesia; 1·4 potash; 4·1 soda; 12 oxides of iron and titanium; 9·2 water; in 100 parts. The tufa stone, which when ground forms trass, is composed of 57·0 silica, 16·0 clay, 2·6 lime, 1·0 magnesia, 7·0 potash, 1·0 soda, 5 oxides of iron and titanium, 9·6 water. This tuff is found abundantly filling up valleys in beds of 10 or 20 feet deep, in the north of Ireland, among the schistose formations upon the banks of the Rhine, and at Monheim in Bavaria. The fatter the lime, the less of it must be added to the ground puzzolana or trass, to form a hydraulic mortar; the mixture should be made extemporaneously, and must at any rate be kept dry till about to be applied. Sometimes a proportion of common sand mortar instead of lime is mixed with the trass. When the hydraulic cement hardens too soon, as in 12 hours, it is apt to crack; it is better when it takes 8 days to concrete. Through the agency of the water, silicates of lime, alumina, (magnesia), and oxide of iron are formed, which assume a stony hardness. Besides the above two volcanic products, other native earthy compounds are used in making water cements. To this head belong all limestones which contain from 20 to 30 per cent. of clay and silica. By gentle calcination, a portion of the carbonic acid is expelled, and a little lime is combined with the clay, while a silicate of clay and lime results, associated with lime in a subcarbonated state. A lime-marl containing less clay will bear a stronger calcining heat without prejudice to its qualities as a hydraulic cement; but much also depends upon the proportion of silica present, and the physical structure of all the constituents. The mineral substance most used in England for making such mortar, is vulgarly called cement-stone. It is a reniform limestone, which occurs distributed in single nodules or rather lenticular cakes, in beds of clay. They are mostly found in those argillaceous strata which alternate with the limestone beds of the oolite formation, as also in the clay strata above the chalk, and sometimes in the London clay. On the coasts of Kent, in the isles of Sheppey and Thanet, on the coasts of Yorkshire, Somersetshire, and the Isle of Wight, &c., these nodular concretions are found in considerable quantities, having been laid bare by the action of the sea and weather. They were called by the older mineralogists Septaria and Ludus Helmontii (Van Helmont’s coits). When sawn across, they show veins of calc-spar traversing the siliceous clay, and are then sometimes placed in the cabinets of virtuosi. They are found also in several places on the Continent, as at Neustadt-Eberswalde, near Antwerp, near Altdorf in Bavaria; as also at Boulogne-sur-mer, where they are called Boulogne-pebbles (galets). These nodules vary in size from that of a fist to a man’s head, they are of a yellow-gray or brown colour, interspersed with veins of calc-spar, and sometimes contain cavities bestudded with crystals. Their specific gravity is 2·59. Analyses of several cement-stones, and of the cement made with them:—
No. 1. English cement-stone, analyzed by Berthier; No. 2. Boulogne stone, by Drapiez; No. 3. English ditto, by Davy; No. 4. reniform limestone nodules from Arkona, by HÜhnefeld; No. 5. cement-stone of Avallon, by Dumas. In England the stones are calcined in shaft-kilns, or sometimes in mound-kilns, then ground, sifted, and packed in casks. The colour of the powder is dark-brown-red. When made into a thick paste with water, it absorbs little of it, evolves hardly any heat, and soon indurates. It is mixed with sharp sand in various proportions, immediately before using it; and is employed in all marine and river embankments, for securing the seams of stone or brick floors or arches from the percolation of moisture, and also for facing walls to protect them from damp. The cement of Pouilly is prepared from a Jurassic (secondary) limestone, which contains 39 per cent. of silica, with alumina, magnesia, and iron oxide. Vicat forms a factitious Roman cement by making bricks with a pasty mixture of 4 parts of chalk, and 1 part of dry clay, drying, burning, and grinding them. River sand must be added to this powder; and even with this addition, its efficacy is somewhat doubtful; though it has, for want of a better substitute, been much employed at Paris. The cement of Dihl consists of porcelain or salt-glaze potsherds ground fine, and mixed with boiled linseed oil. Hamelin’s mastic or lithic paint to cover the faÇades of brick buildings, &c., is composed of 50 measures of siliceous sand, 50 of lime-marl, and 9 of litharge or red-lead ground up with linseed oil. Mosaic gold, the aurum musivum of the old chemists, is a sulphuret of tin. By sealing up muriate of ammonia and sulphuric acid, apart, in a strong glass tube recurved, and then causing them to act on each other, Sir H. Davy procured liquid muriatic acid. He justly observes, that the generation of elastic substances in close vessels, either with or without heat, offers much more powerful means of approximating their molecules than those dependent on the application of cold, whether natural or artificial; for as gases diminish only 1/480 in volume for every degree of Fahrenheit’s scale, beginning at ordinary temperatures, a very slight condensation only can be produced by the most powerful freezing mixtures, not half as much as would result from the application of a strong flame to one part of a glass tube, the other part being of ordinary temperature: and when attempts are made to condense gases into liquids by sudden mechanical compression, the heat instantly generated presents a formidable obstacle to the success of the experiment; whereas in the compression resulting from their slow generation in close vessels, if the process be conducted with common precautions, there is no source of difficulty or danger; and it may be easily assisted by artificial cold, in cases where gases approach near to that point of compression and temperature at which they become vapours.—Phil. Trans. 1823. The muriatic acid of commerce has usually a yellowish tinge, but when chemically pure it is colourless. It fumes strongly in the air, emitting a corrosive vapour of a peculiar smell. The characteristic test of muriatic acid in the most dilute state, is nitrate of silver, which causes a curdy precipitate of chloride of silver. The preparation of this acid upon the great scale is frequently effected in this country by acting upon sea-salt in hemispherical iron pots, or in cast-iron cylinders, with concentrated sulphuric acid; taking 6 parts of the salt to 5 of the acid. The mouth of the pot may be covered with a slab of siliceous freestone, perforated with two holes of about two inches diameter each, into the one of which the acid is poured by a funnel in successive The decomposition of sea-salt by sulphuric acid, was at one time carried on by some French manufacturers in large leaden pans, 10 feet long, 5 feet broad, and a foot deep, covered with sheets of lead, and luted. The disengaged acid gas was made to circulate in a conduit of glazed bricks, nearly 650 yards long, where it was condensed by a sheet of water exceedingly thin, which flowed slowly in the opposite direction of the gas down a slope of 1 in 200. At the end of this canal nearest the apparatus, the muriatic acid was as strong as possible, and pretty pure; but towards the other end, the water was hardly acidulous. The condensing part of this apparatus was therefore tolerably complete; but as the decomposition of the salt could not be finished in the leaden pans, the acid mixture had to be drawn out of them, in order to be completely decomposed in a reverberatory furnace; in this way nearly 50 per cent. of the muriatic acid was lost. And besides, the great quantity of gas given off during the emptying of the lead-chambers was apt to suffocate the workmen, or seriously injured their lungs, causing severe hemoptysis. The employment of muriatic acid is so inconsiderable, and the loss of it incurred in the preceding process is of so little consequence, that subsequently, both in France and in England, sulphate of soda, for the soda manufacture, has been procured with the dissipation of the muriatic acid in the air. In the method more lately resorted to, the gaseous products are discharged into extensive vaults, where currents of water condense them and carry them off into the river. The surrounding vegetation is thereby saved in some measure from being burned up, an accident which was previously sure to happen when fogs precipitated the floating gases upon the ground. At Newcastle, Liverpool, and Marseilles, where the consumption of muriatic acid bears no proportion to the manufacture of soda, this process is now practised upon a vast scale. The apparatus for condensing muriatic acid gas has been modified and changed, of late years, in many different ways. The Bastringue apparatus. At the end of a reverberatory furnace, (see Copper, smelting of, and Soda, manufacture of,) a rectangular lead trough or pan, about 1 foot deep, of a width equal to that of the interior of the furnace, that is about 5 feet wide, and 61/2 feet long, is encased in masonry, having its upper edges covered with cast-iron plates or fire tiles, and placed upon a level with the passage of the flame, as it escapes from the reverberatory. The arch which covers that pan forms a continuation of the roof of the reverberatory, and is of the same height. The flame which proceeds from the furnace containing the mixture of salt and sulphuric acid is made to escape between the vault and the surface of the iron plates or fire tiles, through a passage only 4 inches in height. When the burned air and vapours reach the extremity of the pan, they are reflected downwards, and made to return beneath the bottom of the pan, in a flue, which is afterwards divided so as to lead the smoke into two lateral flues, which terminate in the chimney. The pan is thus surrounded as it were with the heat and flame discharged from the reverberatory furnace. See Evaporation. A door is opened near the end of the pan, for introducing the charge of sea-salt, amounting to 12 bags of 2 cwt. each, or 24 cwt. This door is then luted on as tightly as possible, and for every 100 parts of salt, 110 of sulphuric acid are poured in, of specific gravity 1·594, containing 57 per cent. of dry acid. This acid is introduced through a funnel inserted in the roof of the furnace. Decomposition ensues, muriatic acid gas mingled with steam is disengaged, and is conducted through 4 stone-ware tubes into the refrigerators, where it is finally condensed. These refrigerators consist of large stone-ware carboys, called dame-jeans in France, to the number of 7 or 8 for each pipe, and arranged so that the neck of the one communicates with the body of the other; thus the gas must traverse the whole series, and gets in a good measure condensed by the water in them, before reaching the last. When the operation is finished, the door opposite the pan is opened, and the residuum in it, is discharged, in the form of a fluid magma, upon a square bed of bricks, exterior to the furnace. This paste speedily concretes on cooling, and is then broken into fragments and carried to the soda manufactory. The immense quantity of gas exhaled in discharging the pan, renders this part of the operation very painful to the workmen; and wasteful in reference to the production of muriatic acid. The difficulty of luting securely the cast-iron plates or fire tiles which cover the pan, the impossibility of completing the decomposition of the salt, since the residuum must be run off in a liquid state, finally, the damage sustained by the melting and corrosion of the lead, &c., are among the causes why no more than 80 or 90 parts of muriatic acid at 1·170 are collected, equivalent to 25 per cent. of real acid for every 100 of salt employed, instead of much more than double that quantity, which it may be made to yield by a well conducted chemical process. The cylinder apparatus is now much esteemed by many manufacturers. Fig. 747. After the salt has been introduced, and the fire kindled, 831/4 per cent. of its weight of sulphuric acid, of spec. grav. 1·80, should be slowly poured into the cylinder through a lead funnel, with a syphon-formed pipe. The three-necked carboys may be either placed in a series for each retort, like a range of Woulfe’s bottles, or all the carboys of the front range may be placed in communication with one another, while the last carboy at one end is joined to the first of the second range; and thus in succession. They must be half filled with cold water; and when convenient, those of the front row at least, should be plunged in an oblong trough of running water. The acid which condenses in the carboys of that row is apt to be somewhat contaminated with sulphuric acid, muriate of iron, or even sulphate of soda; but that in the second and third will be found to be pure. In this way 100 parts of sea-salt will yield 130 parts of muriatic acid, of spec. grav. 1·19; while the sulphate of soda in the retort will afford from 208 to 210 of that salt in crystals. It is proper to heat all the parts of the cylinders equably, to insure the simultaneous decomposition of the salt, and to protect it from the acid; for the hotter the iron, and the stronger the acid, the less erosion ensues. Some manufacturers, with the view of saving fuel by the construction of their furnaces oppose to the flame as many obstacles as they can, and make it perform numerous circulations round the cylinders; but this system is bad, and does not even effect the desired economy, because the passages, being narrow, impair the draught, and become speedily choked up with the soot, which would be burned profitably in a freer space; the decomposition also, being unequally performed, is less perfect, and the cylinders are more injured. It is better to make the flame envelope at once the body of the cylinder; after which it may circulate beneath the vault, in order to give out a portion of its caloric before it escapes at the chimney. The fire should be briskly kindled, but lowered as soon as the distillation commences; and then continued moderate till the evolution of gas diminishes, when it must be heated somewhat strongly to finish the decomposition. The iron door is now removed, Liquid muriatic acid has a very sour corrosive taste, a pungent suffocating smell, and acts very powerfully upon a vast number of mineral, vegetable, and animal substances. It is much employed for making many metallic solutions; and in combination with nitric acid, it forms the aqua regia of the alchemists, so called from its property of dissolving gold. Table of Muriatic Acid, by Dr. Ure.
With 2 pounds of very fine flour of mustard, mix half an ounce of each of the following fresh plants; parsley, chervil, celery, and tarragon, along with a clove of garlic, and twelve salt anchovies, all well minced. The whole is to be triturated with the flour of mustard till the mixture becomes uniform. A little grape-must or sugar is to be added, to give the requisite sweetness; then one ounce of salt, with sufficient water to form a thinnish paste by rubbing in a mortar. With this paste the mustard pots being nearly filled, a redhot poker is to be thrust down into the contents of each, which removes (it is said) some of the acrimony of the mustard, and evaporates a little water, so as to make room for pouring a little vinegar upon the surface of the paste. Such table mustard not only keeps perfectly well, but improves with age. The mode of preparing table mustard patented by M. SoyÉs, consisted in steeping mustard seed in twice its bulk of weak wood vinegar for eight days, then grinding the whole into paste in a mill, putting it into pots, and thrusting a redhot poker into each of them. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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