ARTIFICIAL PERFUME-MATERIALS.

In speaking of the volatile oils used in perfumery, two artificial perfume-materials, artificial oils of bitter almonds and wintergreen have already been mentioned. There can be no doubt that when the chemical construction of volatile oils is better known, chemistry will succeed in preparing still more such combinations, valuable for perfumery, or in converting cheap volatile oils into more valuable ones, as has, for instance, been done by Bouchardat and Lafont, who have successfully converted oil of turpentine into oil of lemons. These chemists rectified French oil of turpentine at exactly 311° to 314.6° F., dissolved in the distillate, which amounted to 120 grammes, an equal quantity (120 grammes) of glacial acetic acid, cooled the mixture and then carefully added, so that the temperature never exceeded 104° F., 88 grammes of crystallized chromic acid dissolved in a sufficient quantity of acetic acid. Notwithstanding that the greater portion of the oil of turpentine remained unoxidized, a thorough reaction took place, and the product of decomposition proved to be a hydrocarbon, boiling at from 345.2° to 352.4° F., to which Bouchardat and Lafont have applied the term "terpilene." The properties of this hydrocarbon, especially its boiling point, corresponded with those of oil of lemons, its odor also resembling that of the latter, but it contained about one-sixth cymol which it was impossible to remove. Though thus far this artificial oil of lemons is of no importance for perfumery, it is of interest as showing the possibility of converting one volatile oil into another.

The artificial musk, spoken of under "Musk," cannot be classed with the previously-mentioned artificial perfumed-materials. The odoriferous principle of the natural and artificial musk have nothing in common, the odor depending not on a common chemical combination.

Besides the artificial perfume-materials already mentioned, but a few others are employed in perfumery, viz: Cumarin, heliotropin, vanillin, and nitrobenzol, or oil of mirbane. Another series of artificial perfume-materials, the so-called fruit ethers, have also been recommended for perfumery purposes. Although such products are sometimes used, their employment is not advisable, since they produce an irritating effect upon the bronchial tubes and respiratory organs, and frequently cause headache.

Cumarin.—The agreeable odor of new-mown hay is chiefly due to the sweet-scented vernal grass (Anthoxanthum odoratum, L.). This grass contains an odoriferous substance, the cumarin. The latter is also found in many other plants; for instance, in the tonka bean (the seeds of Dipterix odorata), in the sweet woodruff (Asperula odorata), and, combined with melilotic acid, in the melilot (Melilotus officinalis, Descr.).

Cumarin forms small, colorless crystals of a silky lustre. It is very hard, cracks between the teeth, shows a smooth fracture, and sinks in water. It has a very agreeable aromatic odor, which, on rubbing the substance with the fingers, becomes like that of oil of bitter almonds, and has a bitter, warm, and pungent taste. When pure it melts at 152.6° F., but when containing fat, like that separated from tonka beans, at from 104° to 122° F. Its boiling point lies at 554° F.; it volatilizes, however, at far lower temperatures, diffusing an odor resembling that of oil of bitter almonds, and sublimating in white needles. It is soluble in alcohol, ether, acetic acid, fat, and volatile oils. Of cold water (59° F.) 400 parts are, according to Buchner, required for its solution, but of boiling water only 45 parts.

Tonka beans are the ripe seeds of Dipterix odorata. They are much used in perfumery on account of their content of cumarin, and formerly constituted the initial point for its manufacture. In commerce two varieties are distinguished, viz., Dutch tonka beans, derived from Dipterix odorata, Willd., indigenous to the forests of Guiana, and English tonka beans, from Dipterix oppositifolia, Willd., indigenous to Cayenne.

The Dutch tonka bean is 1.18 to 1.57 inches long, 0.39 to O.59 inch wide, and O.27 to O.43 inch thick. It is generally slightly curved, provided under the point with the hilum, and covered with a thin, fragile, brown-black or black skin of a fatty lustre, upon which small crystals of cumarin are generally found, so that it appears coated, especially in the wrinkles, with a whitish dust. The kernel consists of two yellow-brownish oleiferous catyledons, between which layers of cumarin are generally found. The odor is agreeable, resembling that of melilot, and the taste aromatic bitter. Dutch tonka beans contain fat, sugar, malic acid, and malate of lime; further, starch, gum, and 1 to 5 per cent. of cumarin (C₉H₆O₂). The English tonka beans are smaller, white-yellowish inside, nearly black outside, and of inferior quality to the Dutch beans.

From tonka beans, cumarin may be obtained by two different methods. One method consists in repeatedly extracting the bruised beans with spirit of wine, distilling the latter off from the extract, and mixing the residue with cold water, whereby cumarin contaminated with fat is precipitated. To remove the fat, bring the whole to the boiling point, filter the hot solution through a moist filter upon which the fat is retained, and allow to cool, whereby the greater portion of the cumarin crystallizes out; the remaining small portion is obtained by evaporating the mother-lye.

According to the other method, the bruised tonka beans are distilled with water. After 24 hours the greater portion of the cumarin separates in a crystalline form. The residue remaining in solution can be withdrawn from the water by shaking with petroleum-ether and subsequent evaporation of the solvent. From one pound of good tonka beans, up to 4 drachms of cumarin may be obtained.

Cumarin is sometimes also obtained by purifying by recrystallization of the dÉbris found in the original boxes of tonka beans, which chiefly consists of cumarin.

Perkin has recently succeeded in artificially preparing cumarin from salicylic acid. By boiling the sodium salt of the latter in acetic anhydride for a few minutes and then pouring into water, an oil-like body is separated, whilst sodium acetate passes into solution. The former is a mixture of acetic anhydride, salicylic acid and cumarin; in distilling, the latter passes over last (at 554° F.), and congeals in the receiver to a crystalline mass.

Cumarin is now synthetically prepared by several firms, that brought into the market by Schimmel & Co., of Leipsic, especially being of excellent quality. Although artificial cumarin is considerably lower in price than that obtained from tonka beans, most perfumers still prefer the extract from tonka beans prepared by themselves. There is, however, no good reason for this, since a change in the respective receipts for perfumes presents no difficulties, 8.46 drachms of cumarin corresponding to 2.2 lbs. of best tonka beans.

Heliotropin or piperonal is of great importance in the manufacture of perfumes. It forms small, colorless prismatic crystals, which have an agreeable odor of hÉliotrope. Upon the tongue heliotropin produces the same sensation as oil of peppermint under the same conditions, the sensation being, however, more lasting. It melts at about 104° F., and volatilizes at a higher temperature without leaving a residue. It is soluble in alcohol and ether, and insoluble in cold water; in hot water it melts to an oily liquid which floats upon the water.

Exposed to the action of heat and air, heliotropin acquires an uncomely appearance, balls together and, under very unfavorable circumstances, turns brown. It is then entirely decomposed and useless, and, hence, should be kept in summer in as cool a place as possible. A temperature of 95° F. has already an injurious effect upon the perfume, and it is best not to buy it at all in the hot summer months. To preserve the perfume in its entire freshness, it is advisable for consumers in hot climates to at once dissolve the heliotropin in alcohol and to keep the solution in a cool place.

Pepper serves as the initial point for heliotropin or piperonal, the white variety being the best for the purpose. To obtain piperine, contained in varying qualities (7 to 9 per cent.) in pepper, the latter is repeatedly extracted with boiling alcohol. The extract is then evaporated to one-third its volume, or the greater portion of the alcohol is distilled off, and the resinous mass, obtained after the addition of water, is repeatedly washed in water with the addition of a small quantity of potash or soda lye, dissolved in alcohol and purified by repeated recrystallization. To convert the white-yellow piperine thus obtained into potassium piperate it is, together with equal parts of potassium hydroxide and 5 to 6 parts of alcohol, kept gently boiling for 24 hours in a well-closed flask provided with an ascending Liebig cooler. A capacious flask should be used, as the mass pounds quite vigorously. After cooling, the precipitate, which is obtained in yellowish, lustrous lamina, is separated through a filter from the dark-brown mother-lye, washed with cold alcohol and several times recrystallized from hot water. A further discoloration may be effected by the addition of animal charcoal.

The potassium piperate thus obtained forms nearly colorless prisms in verucose groups, which, however, turn yellow when exposed to light. By boiling the alcoholic mother-lye with ? of the previously used potash-lye, further small quantities of potassium piperate may be obtained.

To obtain piperonal from the potassium piperate, dissolve 1 part of the latter in 40 to 50 parts of hot water, and then slowly introduce, with constant stirring, a solution of 2 parts potassium permanganate in 50 parts of water. This precaution is absolutely necessary, as otherwise the piperonal formed would be partially further oxidized and lost. The paste-like mass formed is passed, while still hot, through a straining cloth, and the residue repeatedly washed with boiling water until it shows nothing more of the characteristic odor of hÉliotrope. The wash-waters are combined with the first filtrate, and subjected to distillation over a free fire.

The first distillates are richest in piperonal, it generally separating already in the cooler. The fractionally caught distillate is allowed to stand one or two days in as cool a place as possible, whereby the greater portion of the piperonal separates in a crystalline form or in fine lamina. To obtain the piperonal still remaining dissolved in the water, the mother-lye, after the separation of the crystals through a filter, may be repeatedly agitated with ether, whereby the piperonal dissolves in the ether. The latter is carefully distilled off at as low a temperature as possible (104° to 122° F.) in the water-bath or allowed naturally to evaporate.

Vanillin.—Vanilla is the not entirely ripe, pod-like, capsular fruit (wrongly called pod), of a tropical orchid (Vanilla planifolia, Andrews), which is cultivated in Mexico, the West Indies, and South America. It is extensively used for flavoring, and its odoriferous substance is highly valued in perfumery. The cross-section of the capsule is thick and fleshy, filled with very small, black, lustrous seeds stuck together by a gummy balsam with which they are coated. The capsule has a sourish taste and has no value, the seeds, or rather the balsam enveloping the seeds, being the substance on which the odor and taste of vanilla depend. When the vanilla fruit becomes ripe, the capsule opens and empties its content of seeds in the form of a balsam-like mass.

The lustrous black-brown surface of vanilla is frequently coated with white, delicate crystals, which were formerly taken for benzoic acid. Bley and Vee first recognized them as a peculiar substance, which was further examined by Gobley and Stokkebye. This substance, to which Gobley applied the term vanillin, is the chief odoriferous substance of vanilla. It is deposited upon the vanilla-crystals, when the latter are densely and closely packed together and for some time exposed to a heat of about 77° F. Of vanillin, vanilla contains 1.5 to 2.75 per cent.; the Mexican variety containing 1.69 to 1.32 per cent., the Bourbon No. I, 2.48 to 1.91 per cent., Bourbon No. II, 1.55 to 0.75 per cent., and the Java, 2.75 to 1.56 per cent. It is singular, that the highly valued Mexican vanilla has, generally speaking, a lower content of vanillin than the other varieties.

At present, vanillin is prepared artificially. Tiemann and Harmann first showed that by the oxidation of coniferin, a glucoside occurring in the cambial sap of the ConiferÆ, a product, perfectly identical with the vanillin prepared from vanilla, is obtained. The coniferin is obtained by barking the pine or silver fir, scraping together the sap under the bark together with a portion of the liber and pouring it into a vessel. The sap is then pressed off, boiled to separate the albumin, filtered, evaporated to one-fifth its volume, and set aside to crystallize. One hundred quarts of sap are said to yield from 1 to 2 pounds of coniferin-crystals. By now allowing an aqueous coniferin-solution to run into a heated mixture of 10 parts potassium bichromate, 15 parts concentrated sulphuric acid, and 80 parts water, and heating for 3 hours in a flask with back-flow cooler, a liquid is obtained from which ether takes up a yellow oil. After treating the latter with animal charcoal, dissolving in ether and evaporating the latter, there remain colorless, acicular crystals of the odor and taste of vanilla. These crystals consist of vanillin contaminated with some vanillic acid. To separate the latter, purify with acid sodium sulphite and recrystallize. After this operation, vanillin represents a nearly white crystalline powder which melts at from 176° to 177.8° F. In this form it is brought into commerce as a complete substitute for vanilla, 5.64 drachms of it corresponding to about 1 pound of vanilla. A medium-sized pine tree is said to yield vanillin of the value of 80 marks ($19.20).

Vanillin may also be prepared by oxidation from eugenol. Oil of cloves is diluted with three times its volume of ether and agitated with weak caustic potash solution to fix the eugenol on the potash. By acidulating the alkaline solution and shaking with ether, the eugenol is collected. After distilling off the ether, the eugenol is converted with acetic anhydride into aceteugol, and the latter oxidized with dilute, moderately-warmed potassium permanganate solution. The filtrate is made slightly alkaline, concentrated, then compounded with acid and the vanillin extracted with ether.

Vanillin (C₈H₈O₃) forms small colorless prisms of a strong vanilla odor, a warm, vanilla taste, and an acid reaction. It is readily soluble in hot water, alcohol, ether, chloroform, fat and volatile oils, as well as in solutions of caustic alkalies and alkaline carbonates. It melts when heated to from 176° to 177.8° F.; at a higher temperature it sublimates without leaving a residue.

According to a notice published in the "Deutsch-Amerikanischen Apotheker Zeitung," vanillin adulterated with benzoic acid has occurred in the United States. A sample subjected to examination is said to have been nothing but benzoic acid perfumed with vanillin. Such an adulteration can be detected with the microscope, since vanillin crystallizes in acicular crystals, and benzoic acid in lamina, which can be readily recognized. Pure vanillin melts at 176° F., while the melting points of such mixtures are considerably higher, it being in one case at 249° F. By extracting such mixture with thin sodium carbonate solution, benzoic acid passes into solution. After neutralizing with hydrochloric acid, the filtrate yields with ferric chloride a fawn-brown precipitate of ferric benzoate, and on adding hydrochloric acid in excess, the benzoic acid, which dissolves with great difficulty in cold water, is precipitated. By treating the latter, or the ferric benzoate, with dilute sulphuric acid and magnesium, the benzoic acid is reduced to benzaldehyde, which is recognized by its characteristic odor of oil of bitter almonds.

Nitrobenzol is obtained by treating benzol, or a mixture of it, with toluol and their higher homologues, with strong nitric acid, or a mixture of nitric and sulphuric acids, washing the product of reaction with water and soda, caustic soda or ammonia, expelling the unaltered hydrocarbons with steam and rectifying the residue. Three varieties distinguished by their boiling points and odor occur in commerce. The nitrobenzol or oil of mirbane (essence de mirbane) is the so-called light nitrobenzol, which boils at from 401° to 415° F. The heavier varieties boil at a higher temperature and have a more or less disagreeable odor; they are used in the manufacture of aniline and aniline colors.

Pure oil of mirbane is pale yellow, the finest qualities being colorless and almost as clear as water. It has an agreeable odor resembling that of oil of bitter almonds, a specific gravity of 1.186 to 1.2 = 25° BÉ., and congeals at 37.4° F. to a crystalline mass. It is scarcely soluble in water, sparingly so in alcohol and with difficulty in watery spirit of wine; it is miscible in all proportions with ether, benzine, volatile oils, and most fat oils.

Oil of mirbane is largely manufactured in England, but the German product is now generally preferred, it being purer and does not impart to soap perfumed with it a yellowish tinge. The finest oil of mirbane is prepared from pure crystallizable benzol, and again purified by washing with potassium bichromate and sulphuric acid, and by rectification with steam.

Pure nitrobenzol suffers no change by boiling with soda lye, while the poorly rectified product colors the lye yellow or brown.

Nitrobenzol is frequently adulterated with spirit of wine, which is recognized by shaking the oil with fat oil of almonds; in the presence of spirit of wine a turbid mixture is formed. By shaking nitrobenzol containing spirit of wine with an equal volume of water in a graduated cylinder, its volume decreases.

Oil of mirbane is much used for perfuming soaps, but even the finest quality of it cannot replace oil of bitter almonds for fine soaps and perfumery. Great care has to be exercised in storing, as well as in working, nitrobenzol, it igniting very readily, and it is also poisonous. Even the vapors, when inhaled for some time, may produce symptoms of poisoning, which consist in the skin acquiring a leaden color, and heavy feelings in the limbs with cold extremities, especially the hands and feet.

Fruit Ethers. At the London Exhibition, in 1851, various products called apple oil, pear oil, pine-apple oil, etc., were shown. They were examined by A. W. Hofmann, and found to consist of solutions of certain ethers in alcohol. Since then the manufacture has greatly increased and large quantities are now brought into commerce under the name of fruit ethers or fruit essences.

Fruit ethers are fluids possessing an agreeable, refreshing odor closely resembling that of some fruits. For this reason they are used in confectionery, in the manufacture of liqueurs and also as a substitute for volatile oils, in the manufacture of perfumery. Chemically, fruit ethers are combinations of an organic acid—acetic, butyric, valerianic, etc.—with a so-called alcohol radicle, such as ethyl and amyl. The preparation of fruit ethers being connected with many difficulties, is seldom attempted by perfumers, especially as products of an excellent quality can at a low rate be procured from chemical laboratories making a specialty of their manufacture. However, for the sake of completeness, a brief description of the fabrication of the principal ethers used in their preparation shall here be given.

Acetic amyl ether or amyl acetate, C₅H₁₁O.C₂H₃O, is prepared by mixing 1 part of amyl alcohol with 1 part of concentrated sulphuric acid, and distilling the mixture with 2 parts of potassium acetate. The distillate is washed with water, to which some carbonate of soda has been added, and then rectified over magnesia. It forms a colorless liquid of an agreeable fruity odor. It boils, according to Kopp, at 280° F. and, at 59° F., its specific gravity is 0.8692.

For use in perfumery, the ether is best prepared, according to Fehling's directions, by heating for some time at a temperature of 212° F. 1 part of glacial acetic acid with ½ part of sulphuric acid and one part of amyl alcohol. By then adding water the ether is separated. By this process distillation is avoided.

Acetic ethyl ether or ethyl acetate, C₂H₃O.O.C₂H₅. Acetic ether is formed by the decomposition of sodium acetate by ethyl sulphuric acid:—

One molecule of sulphuric acid or 98 parts is mixed with one molecule of alcohol or 46 parts, or with 1 molecule of alcohol of 90 per cent. which contains 85.75 per cent. of absolute alcohol, hence with 53.6 parts of alcohol, and distilled with 1 molecule or 82 parts of anhydrous sodium acetate. Since commercial sulphuric acid always contains 5 or 6 per cent. of water, this has to be taken into consideration, and 105 to 106 parts of it have to be used in order to decompose the entire quantity of sodium acetate. The crude sodium acetate found in commerce may be used. It is nearly white and at the utmost contaminated by traces of sulphuric acid and chlorine, which in this case are not injurious. The crystallized salt is heated in an iron kettle whereby it melts in its water of crystallization. With constant stirring the water is then completely evaporated until an entirely dry mass of salt remains behind. The latter may be quite strongly heated without fear of destroying the acetic acid. The dried salt is immediately powdered, passed through a medium fine sieve and kept for use in well-closed vessels.

On a large scale the distillation of the ether may be effected in an iron kettle, which is provided with a well-fitting lid and connected by a copper head with a cooling apparatus—a worm lying in cold water. Bring into the kettle the required quantity of concentrated sulphuric acid, add, with vigorous stirring, the alcohol and allow the mixture to rest for 24 hours. Then throw the dry sodium acetate into the mixture, mix it thoroughly, by stirring, with the ethyl sulphuric acid, and, after luting all the joints of the apparatus, heat at first moderately. Distillation proceeds quietly and uniformly, the fire being regulated according to how the ether runs off from the worm. Such uniform distillation is, however, only attained by the use of the sodium acetate in the form of powder, and thoroughly mixing it with the acid. If large pieces of the salt are present or the powdered salt balls together, the formation of ether sometimes takes place so suddenly that the vapors cannot condense in the cooling apparatus, but escape violently, or if they cannot escape rapidly from the condenser, may even burst the apparatus. The reason for this is that the larger pieces float in the superheated acid without being saturated by it, and, when they suddenly collapse, form a mass of ether-vapors.

Distillation is continued until that which at last passes over is not inflammable. With the above-mentioned proportions 88 parts of acetic ether are formed, but as some water always passes over, distillation need not be interrupted until the receiver contains at least 90 parts of crude ether.

The crude ether always contains more or less water, some alcohol, and a small quantity of free acetic acid. With the above-mentioned proportions, the content of alcohol can, however, be only very small. To neutralize the acetic acid, add some burnt magnesia or shake with carbonate of soda solution until the acid reaction disappears. For the absorption of the water and alcohol, add as much sharply dried (not fused) calcium chloride as the fluid will dissolve, and then let it stand with an excess of the salt for one day. The calcium chloride combines with the water and alcohol and separates as a heavy layer beneath the ether. The latter is decanted off and brought into a rectifying vessel—a copper still, heated by steam, and provided with a cooling pipe. The ether is distilled off at a moderate heat, the last portion, about 1/10, being caught in a special receiver, to be again rectified at the next operation.

According to Grossschopf, 40 lbs. of pulverized anhydrous sodium acetate, together with a cooled mixture of 46 lbs. of concentrated sulphuric acid and 37 lbs. of 95 per cent. alcohol, free from fusel oil, are distilled in a copper still heated by steam. Distillation is continued with constant stirring by means of an apparatus in the still, until no more fluid smelling and tasting of acetic ether passes over. The crude distillate, amounting to 55 or 56 lbs., is brought into bottles which are filled ? full. The bottles are then filled up with water and potassium carbonate is added until the fluid, after shaking, shows no acid reaction. The aqueous fluid beneath the ether is then drawn off by means of a siphon, and the ether several times washed by shaking with water and allowing to settle. Since the wash-water absorbs a quite considerable quantity of ether, it is collected and subjected to rectification, whereby an alcoholic acetic ether is obtained. The ether, being freed from acetic acid and alcohol by neutralization and washing, is brought in contact with fused calcium chloride to free it from water, and finally rectified over magnesia. In this manner 36 to 37 lbs. of pure acetic ether are obtained.

Acetic ether is a clear, colorless fluid of a pleasant, etheral odor. It boils at 170.6° F., and at 59° F. its specific gravity is 0.9068. Pure acetic ether dissolves in 11 to 12 parts of water; a content of alcohol or the addition of water increases its solubility. Hence, its solubility in water is a criterion of its purity.

Benzoic ether or ethyl benzoate, C₇H₅O.OC₂H₅, is most readily prepared by mixing 4 parts of alcohol, 2 parts of crystallized benzoic acid, and 1 part fuming hydrochloric acid, and for some time heating the mixture in a flask. The benzoic acid is thereby gradually and completely converted into ether. The fluid is mixed with water, whereby the ether is completely separated. It is several times washed with carbonate of soda solution, and, for the purpose of withdrawing the last trace of free acid, distilled over lead oxide. It forms a colorless oil of an aromatic odor, specific gravity 1.0502, and boils at 412° F. In cold water it is insoluble. However, like all varieties of ether, it dissolves readily in alcohol and ether.

Butyric ethyl ether or ethyl butyrate, C₄H₇O.OC₂H₅. The preparation of this ether must be preceded by that of butyric acid. The latter is obtained, according to Bensch, by dissolving 6 lbs. of cane sugar and 8 drachms of tartaric acid in 13 quarts of hot water, allowing the liquid to stand a few days and then adding 7 ozs. of old rotten cheese, which has been stirred up in 4 quarts of skimmed sour milk and 3 lbs. of finely pulverized chalk. The mixture must be kept at a uniform temperature of from 86° to 95° F. for some weeks, from time to time mixing it by stirring, and replacing the water lost by evaporation.

By the action of a ferment the sugar is first converted into lactic acid. In 10 to 12 days the entire mass congeals to a paste of calcium lactate. By now allowing fermentation to proceed without interruption, it gradually enters another stage; gas bubbles consisting of carbonic acid and hydrogen rise up, until in the course of 5 or 6 weeks the process is finished. This is recognized by the fluid becoming quiet, no more gas being evolved. The fluid then contains a solution of calcium lactate, which is converted into the corresponding sodium salt by the addition of 8 lbs. of crystallized soda. It is then filtered and concentrated by evaporation to 5 quarts. By adding 5½ lbs. of sulphuric acid, diluted with an equal volume of water, butyric acid is separated as a dark-colored oily mass.

The crude butyric acid thus obtained and freed from water by shaking with calcium chloride, is a mixture of acetic, butyric, and capric acids, but does not contain propionic and valerianic acids. To obtain from it pure butyric acid, fractional distillation is required. For manufacturing on a large scale, a copper distilling apparatus with silver head and silver cooling pipe is used, the bulb of a thermometer being placed in the head. In the first rectification, the receiver is changed after the thermometer has risen to 311° F.; the portion passing over between 311° and 329° F. is caught up by itself, and the receiver being again changed, distillation is continued until finished. The first distillate contains mostly acetic acid, besides a small quantity of butyric acid, the second the greater portion of the butyric acid besides a little acetic and capric acids, while the third consists chiefly of capric acid. For preparing butyric ether for technical purposes, the fraction passing over between 311° and 329° F. is sufficiently pure. To obtain chemically pure butyric acid, the rectification of the portion passing over between 311° and 329° F. is in the same manner repeated, until finally a product with a constant boiling point at 324.2° F. is obtained.

Butyric acid fermentation proceeds more rapidly by using, instead of rotten cheese, putrefying meat, and in place of sugar, starch paste or mashed boiled potatoes, 1 part of meat to 4 parts of starch or a corresponding quantity of potatoes being employed. The same products are formed as in the preceding process, but much more rapidly, fermentation being finished, according to Schubert, in 5 to 6 days.

Butyric acid, C₄H₇O.OH, or C₃H₇COOH, is a liquid of a very sour taste and odor, and at an intense cold congeals to a crystalline mass which melts at 32° F. In a pure state it boils at 324.2° F. It is soluble in water, but separates again if soluble salts are added to this solution. Its specific gravity, after being completely freed from water, is 0.974.

Besides the normal butyric acid, there is known another one called isobutyric' acid or dimethyl acetic acid. It is distinguished from the normal acid by being less soluble in water and by its boiling point, which lies at 309.2° F. It occurs in St. John's bread or carob, in the volatile oil from Arnica montana and in croton oil.

Butyric ether is formed by mixing 2 parts of butyric acid with 2 parts of alcohol and 1 part of sulphuric acid. The fluid is heated to 176° F., and, after being for several hours kept at that temperature, is poured into cold water, whereby the ether separates as an oily fluid. It is then separated from the aqueous solution, washed with water to which some chalk has been added for the neutralization of the free acid, and finally the water is withdrawn from the ether by, for several days, leaving it in contact with calcium chloride. To obtain it entirely pure, it is only necessary to distil it once. It forms a clear, very mobile fluid of a pine-apple odor, and a specific gravity of 0.900. It boils at 249.8° F.

Commercial butyric ether, large quantities of which are used for the preparation of the so-called pine-apple ether or essence, is seldom pure, it being generally obtained from simply rectified butyric acid. According to another method, which is, however, not as profitable, it is obtained by distilling butter-soap with alcohol and sulphuric acid. For this purpose, bring 20 pounds of butter-soap, cut up in small pieces, into a distilling apparatus, pour over it 10 pounds of 90 per cent. alcohol and heat moderately until the soap is dissolved. Since a portion of the alcohol evaporates thereby, add 10 pounds more of alcohol and then 20 pounds of sulphuric acid. On further heating, a fluid of a very agreeable odor distils over, which is an alcoholic solution of the ethers of the volatile acids found in butter. Towards the end of the operation, in consequence of the further progress of decomposition, a development of sulphurous acid generally takes place. This is removed from the distillate by allowing it to remain for several days in contact with finely-pulverized pyrolusite (peroxide of manganese) and rectifying over burnt magnesia. In the first distillation, the heavy volatile acids of the butter remain behind; they are freed from the excess of sulphuric acid and the sulphate of sodium or potassium by washing with hot water, and can be utilized in the manufacture of soap.

The butyric ether obtained from butter-soap is far from being pure butyric ether, it containing, besides it, a mixture of various kinds of ether derived from the volatile acids—caproic, capric, and caprylic acids. However, these varieties of ether possess similar properties to that of butyric acid; in alcoholic solutions their taste and odor are nearly alike, and hence can be employed in this mixture for the preparation of essences of an agreeable odor and taste.

A suitable material for the preparation of butyric ether is also the St. John's bread or carob, the pods of Silequa dulcis. Redtenbacher established in them the occurrence of about 2 per cent. butyric acid, which Gruenzweig later on proved to be isobutyric acid. Besides butyric acid and other volatile acids, St. John's bread contains about 40 per cent. of fermentable varieties of sugar, which can be utilized after their conversion to butyric acid. For this purpose Stinde has proposed the following process: Convert the pods together with the seeds to a coarse powder; bring 100 lbs. of this powder into a capacious barrel placed in a warm place, and pour sufficient water of 82.5° F. over it, to form a thin paste; after 4 to 5 days add 24 lbs. of whiting and await fermentation. The paste, which gradually becomes thicker, is from time to time stirred, and, if necessary, a small quantity of lukewarm water added. In summer fermentation is finished in six weeks, after which the preparation of the ether is proceeded with.

For this purpose bring the paste into a still provided with a steam jacket; the evening before mix 36 lbs. of concentrated sulphuric acid with 60 lbs. of alcohol of 95 per cent., and add the mixture to the paste in the still; then lute the joints of the distilling apparatus, and quickly introduce steam. Distillation soon commences, and, when once introduced, is continued with a moderate admission of steam.

The first pound of the distillate is caught by itself, and, after changing the receiver, distillation is continued until but little passes over, even with an increased admission of steam. Thus an abundant yield of alcoholic butyric ether is obtained. When distillation is finished 20 lbs. more of alcohol may be brought into the still; the distillate obtained thereby being still rich in butyric ether.

The St. John's bread used should be of the best quality, free from worms and mould, as otherwise the ether would not possess the pure, agreeable odor characteristic of butyric ether.

Formic ethyl ether, or ethyl formate, CHO.OC₂H₅.—This ether is also much manufactured for the preparation of the so-called essences which are employed for the purpose of imitating the odor of plants, fruits, etc. It is formed by the action of formic acid upon alcohol, or by bringing ethyl sulphuric acid, or a mixture of alcohol and sulphuric acid, in contact with formates, or finally by bringing formic acid at the moment of its formation in contact with alcohol.

The most simple process is that recommended by Lorin:—

Into a capacious distilling apparatus connected with the cooling pipe, so that the distillate constantly flows back, bring 1 part, by weight, of glycerin of the consistency of syrup, add ¼ of its weight of crystallized oxalic acid and the same quantity of alcohol of 90 to 95 per cent. With moderate heating a vigorous development of gas soon takes place. The oxalic acid in contact with the glycerin splits into formic acid and carbonic acid, according to the following equation:—

The glycerine does not undergo alteration thereby. The nascent formic acid converts the alcohol present into formic ether, water being separated. When, after continued heating, the development of carbonic acid abates, add the same quantities of oxalic acid and alcohol to the contents of the still, heat again until but little carbonic acid is evolved, and then add, twice in succession, the same quantities of oxalic acid and alcohol as before, until finally as much oxalic acid is consumed as glycerin has been employed. When the evolution of carbonic acid ceases, the receiver is reversed and the ether distilled off. The glycerin remaining behind is again concentrated to the consistency of syrup, and may be re-used.

The distillate is freed from free acid by the addition of magnesia, and the alcohol and water are separated by shaking with calcium chloride, after which the pure ether is obtained by rectification.

Formic ether is colorless, thinly-fluid, of a pleasant smell, specific gravity 0.945, boiling point 130° F., soluble in cold water, and miscible in every proportion with alcohol and ether.

Nitrous ether, or ethyl nitrite, C₂H₅.ONO.—In a pure state this ether is best prepared according to the method given by E. Kopp. It consists in bringing equal volumes of alcohol and ordinary nitric acid together with copper filings into a distilling apparatus, which is so arranged that the vapors first pass through a flask filled with water of 77° F., then through a calcium chloride tube, and are finally condensed in a receiver surrounded by snow and common salt. The nitric acid is first decomposed by the copper, nitrous acid being thereby developed, which is so transposed that its radicle NO occupies the position of the typical hydrogen in the alcohol, while the rest of the acid forms water with the hydrogen of the alcohol. By the reaction such a quantity of heat is liberated that the process requires assistance by external heating only towards the end of the operation. In the receiver is then a pale yellow fluid having the taste and odor of apples and, at 59° F., a specific gravity of 0.947. According to Liebig, the boiling point of nitrous ether lies at 61.5° F.; hence it can be condensed only by careful cooling, and has to be kept in glass tubes fused together. In water it is but sparingly soluble, but readily so in alcohol. By the addition of water it is separated from the alcoholic solution.

Mohr has modified Kopp's method as follows: Mix alcohol of 0.833 specific gravity, water, and nitric acid of 1.200 specific gravity, each 24 parts and add 4 parts of copper filings. Of this mixture draw off 24 parts of distillate, mix the latter with litmus tincture and neutralize the free acid by adding, drop by drop, solution of caustic potash or soda until the litmus tincture becomes blue. Rectify the distillate and catch of it 8 parts. Compound the latter with 16 parts alcohol of 0.833 specific gravity, whereby the product is made equal to the quantity of alcohol originally used. The product is kept in glasses holding from 2 to 3 ozs. each. This alcoholic nitrous ether is of a yellow color, very strong and has a pure odor.

In England and America, nitrous ether is much used for aromatizing whiskies and for other purposes. According to Stinde[9] it is prepared on a large scale as follows:—

A stone-ware flask of at least 120 lbs. capacity, such as is used for the preparation of chlorine, is so placed upon a tripod in a sheet-iron cylinder that the neck projects over the edge of the cylinder. The space between the flask and the walls of the cylinder is completely filled with mats or coarse pack-cloth. A steam-pipe enters the lower part of the cylinder, while a cock placed on the bottom of the cylinder serves for discharging the condensed water. The cylinder is closed by a sheet-iron cover provided in the centre with a hole through which passes the neck of the flask. The flask is filled with 60 lbs of 90 per cent. alcohol free from fusel oil, to which, in small portions, 15 lbs. of crude nitric acid of 36° BÉ. are added.

The neck of the flask is provided with an exactly-fitting tube of pure tin. The tube is bent twice at a right angle, and one end is provided with an annular piece to prevent it from slipping too far into the interior of the flask. The joints between the tube and the neck of the flask are luted with a stiff paste of flaxseed meal, a wet strip of linen being, for greater security, wrapped over the cement. The other end of the tin-tube, which here occupies the place of a still-head, is in the same manner connected with a long tin-worm lying in a large cooling vat.

Everything being prepared, but little steam is at first introduced into the iron cylinder in order to slowly warm the apparatus. When this is done the admission of steam is gradually increased. The mats or pack-cloth placed between the walls of the cylinder and the flask prevent the latter from bursting, which otherwise might readily happen. Distillation commences in about ten minutes. The admission of steam is then moderated, care being had that the ether passes over in an uninterrupted stream of the thickness of a goose-quill.

When, with the admission of the same amount of steam, the distillate commences to run drop by drop, the steam-cock is closed and the operation interrupted, this being the case in about six to seven hours.

The next day the flask—without removing the residue—is charged in the same manner. However, the third day only 30 pounds of alcohol are poured in.

The combined distillates come into a copper still with double walls, between which steam can be admitted, and are neutralized with dry calcium hydrate. The cooling pipe connected with the still consists of tin, and is provided with a beak dipping into a flask filled half-full with 4 pounds of alcohol. A slight current of steam suffices for distillation. The first distillate is dark yellow, and contains large quantities of aldehyde. Notwithstanding careful cooling, the vapors can be but incompletely condensed, and their inhalation has to be carefully avoided, they producing stupor and headache as well as inflammation of the eyes. When the distillate is colorless and shows no reaction with litmus paper, the receiver is removed and replaced by a large glass balloon in which the entire distillate is collected. Distillation must be quickly finished, as otherwise colored ether is obtained.

Valerianic amyl ether or amyl valerate, C₅H₁₁O.C₅H₉O.

This ether is formed by treating amyl alcohol with chromic acid. However, besides the ether a large quantity of valerianic acid is also formed, which has to be converted by itself into ether.

To prepare the ether bring 5½ parts of powdered potassium dichromate together with 5 parts of water into a distilling apparatus and very gradually add a mixture of 1 part amyl alcohol and 5 parts concentrated sulphuric acid. The fluid becomes so strongly heated that it almost boils. When reaction is finished, heat and distil off the rest. The distillate consists of two layers; the lower one being an aqueous solution of valerianic acid and the upper one a mixture of valerianic acid and amyl valerate. To separate both, add concentrated carbonate of soda solution until all the free acid is neutralized. The oily liquid separating thereby is the ether. It is separated from the valerianate of sodium, the latter evaporated to a small volume, and, after cooling, sufficient sulphuric acid to fix the entire quantity of the soda is added. The valerianic acid is thereby separated, and floats upon the solution of the sodium sulphate. It is separated from the latter, and 1¼ parts of it are added to a mixture of ¾ part of amyl alcohol and 1 part sulphuric acid and heated to 212° F. After the addition of water, the apple-ether separates and only requires washing with water and some sodium carbonate to yield a pure product.

The separation of the valerianic acid can, however, be readily avoided. Evaporate the neutral solution of the valerianate of soda to dryness in the water-bath, weigh off 1 molecule, or 124 parts, and gently heat it with a mixture of 1 molecule or 98 parts of sulphuric acid (on account of the content of water in the commercial acid, 105 parts of it will have to be taken) and 1 molecule or 88 parts of amyl alcohol.

The ether thus obtained is a fluid, which, in a concentrated state, does not possess an agreeable odor, but when mixed with 10 parts of alcohol imparts to the latter an odor resembling that of apples. It boils at from 370° to 374° F., and at 64° F. has a specific gravity of 0.8793.

Valerianic ethyl ether closely resembles the amyl ether, and, like it, is prepared from valerianate of sodium, ordinary alcohol, and sulphuric acid.

Apple ether essentially consists of valeric amyl ether, of which 1 part is dissolved in 6 to 10 parts of strong alcohol.

Apricot ether is butyric ether with some amyl alcohol.

Cherry ether is acetic ether with benzoic ether.

Pear ether contains acetic amyl ether.

Pineapple ether is butyric ether.

Strawberry ether is acetic ether with acetic amyl ether and butyric ether.

The ethers are dissolved in various proportions in alcohol, according to the intensity of the odor which it is desired to obtain. The aroma of most of them is generally increased by a slight addition of chloroform.

For the preparation of different fruit essences Kletzinsky[10] gives the following directions. The figures indicate additions in cubic centimeters to 1 liter of rectified alcohol of 90 per cent.:—

Apple essence.—Chloroform 10, nitrous ether 10, aldehyde 20, acetic ether 10, valeric amyl ether 100, oxalic acid[11] 10, glycerin 40.

Apricot essence.—Chloroform 10, butyric ether 100, valeric ether 50, peach oil 10, amyl alcohol 20, butyric amyl ether 10, tartaric acid[11] 10, glycerin 40.

Cherry essence.—Acetic ether 50, benzoic ether 50, peach oil 10, benzoic acid[11] 10, glycerin 30.

Currant essence.—Aldehyde 10, acetic ether 50, benzoic ether 10, grape-seed oil 10, tartaric acid[11] 50, succinic acid[11] 10, benzoic acid[11] 10.

Grape essence.—Chloroform 20, aldehyde 20, formic ether 20, grape-seed oil 100, wintergreen oil 10, tartaric acid[11] 50, succinic acid[11] 30, glycerin 100.

Lemon essence.—Chloroform 10, nitrous ether 10, aldehyde 20, acetic ether 100, oil of lemons 100, tartaric acid[11] 100, succinic acid[11] 10, glycerin 50.

Melon essence.—Aldehyde 20, formic ether 10, butyric ether 40, valeric ether 50, glycerin 30.

Orange essence.—Chloroform 20, aldehyde 20, acetic ether 50, formic ether 10, butyric ether 10, benzoic ether 10, wintergreen oil 10, acetic amyl ether 10, orange-peel oil 100, tartaric acid[11] 10, glycerin 100.

Peach essence.—Aldehyde 20, acetic ether 50, formic ether 50, butyric ether 50, valeric ether 50, peach oil 50, amyl alcohol 20, glycerin 50.

Pear essence.—Acetic ether 50, acetic amyl ether 100, glycerin 100.

Pineapple essence.—Chloroform 10, aldehyde 10, butyric ethyl ether 50, butyric amyl ether 100, glycerin 30.

Plum essence.—Aldehyde 50, acetic ether 50, formic ether 10, butyric ether 20, peach oil 40, glycerin 80.

Raspberry essence.—Nitrous ether 10, aldehyde 10, acetic ether 50, formic ether 10, butyric ether 10, benzoic ether 10, grape-seed oil 10, wintergreen oil 10, acetic amyl ether 10, butyric amyl ether 10, tartaric acid[11] 50, succinic acid[11] 10, glycerin 40.

Strawberry essence.—Nitrous ether 10, acetic ether 50, formic ether 10, butyric ether 50, wintergreen oil 10, acetic amyl ether 30, butyric amyl ether 20, glycerin 20.