Before beginning a description of manufacturing processes, a precise definition of leather may be given. Laymen usually describe leather as "hides tanned with bark," Since the introduction of modern processes, however, this is only partly true. In any case, the definition is very broad.

The primary objects of treating raw hides and skins to produce leather is to make them imputrescible and impart various degrees of pliability. These qualities are essential, but the simpler the methods used to attain them, the greater the strength of the leather produced.

The number of materials that will produce leather is legion. Whereas oak bark was almost exclusively used for tanning until the last century, there are now at least twenty useful vegetable tanning materials. The active ingredient of all of these materials is tannin, a colloidal or uncrystallisable substance. Correctly speaking, the term "tanning," used to designate the process of converting hides into leather, should be confined to the use of vegetable tannins; unfortunately, the trade has largely adopted the word in many other processes of making leather. For example, large quantities of leather are produced by the use of minerals, and especially of chrome salts; where the latter is used, the leather is said to be "chrome-tanned," although "chromed" would be a more accurate definition. One mineral process of making leather, namely, that involving the use of alum, or alumina sulphate, and salt, is technically described as "tawing," The conversion of skins into leather by the use of oxidised oil is known as "chamoising," imitation chamois leather being made by that process. Nearly every mineral has the property of converting skins into leather, though most of them are of little practical value. The most successful are the chrome salts, and alum and salt. The use of iron salts would be by far the cheapest process, if means could be found whereby they could be successfully used. Sixty years ago, a chemist named Knapp experimented with iron salts, but failed to produce satisfactory leather. Patents were taken out in Austria in the early part of 1914 for the use of iron salts in tanning, while a patent of more recent date covers the use of iron salts in combination with chrome salts. Neither of these appears to be of much practical value. The cheapest and most stable iron salts, the sulphate and chloride, have strongly acidic properties, and, therefore, have a somewhat destructive and hardening effect on animal fibres. The iron salt that might convert skins into leather is the carbonate, which is difficult to prepare cheaply enough for commercial purposes, though it is used medicinally. A basic iron salt might also be useful, but iron tannages would only be suitable for black leather. Oils and fats also have leather-making properties, fish oils being used for the manufacture of "chamois" and antelope leather. There are other methods of producing leather which are not used on a large scale, but sufficient examples have been given to show that an exact definition of leather cannot be summed up in one or two words. There are now many kinds of leather produced by varying methods, and each class requires its own definition. Broadly speaking, however, leather is an imputrescible material produced from the raw skins of animals, chiefly of cattle, sheep, and goats, by treating them with tannins extracted from the barks, wood, fruit, or leaves of trees; or with chemicals (chiefly chrome salts, or alum and common salt); or with oils and fats.

The preliminary processes are of great importance, as they determine to a large extent the character of the finished leather. Mistakes made in the early processes can never be effectually remedied.

The first operation is technically known as soaking, and its object is to cleanse the hides or skins thoroughly. This is quite simple in the case of raw hides received direct from the slaughterhouse, as it is merely a question of soaking them in clean, soft water for a few hours. If the only water available is hard, 1/2 lb. of borax should be added for every 100 lb. of raw hides. Borax is useful in any case, as it is a splendid cleanser and a very useful chemical in the tannery. Most of the hides used in the United Kingdom, however, are wet-salted (i.e., salted in the wet state), as it has become customary for most butchers to send hides and skins to the auction markets in all the principal towns, where they are offered for sale every week. It is still a debatable point among tanners as to whether it is better to buy hides direct from the butcher or through these markets. It is certainly a great advantage to put hides into work quickly (although not before they are quite cool), as time is saved in the soaking process, and there is practically no loss of gelatinous matter. On the other hand, the tanner is able to buy just the selection of hides that he wants from the auction markets. Under this arrangement, several days must elapse before the tanner receives them, and it is, therefore, absolutely necessary to preserve them, otherwise they begin to decompose quickly. The first sign of decay is the slipping of the hair, which, in that condition, may be pulled out of its roots quite easily. Micro-organisms multiply rapidly in the gelatine of the hide, the grain comes away, and decomposition sets in so quickly that, in a few days after the removal of the hide from the carcase, it may lose nearly half its value for tanning purposes if it has not been preserved by salting or by drying rapidly in the shade in a current of air. Salted hides need a more prolonged soaking than fresh hides, as it is essential that all trace of salt be removed before the next process, otherwise the finished leather may be flat, and poor in quality. Usually, two days' soaking in several changes of water is necessary. For the soaking process, fresh or salted hides and skins are either soaked in square, cement-lined, brick pits, or in wooden vats filled with clean, cold water. A good system is to put a pack of skins in one huge tank filled with clean water and leave them in soak overnight before transferring them to the ordinary pits. Each pit will take 50 hides, or 10 dozen calf skins, or 20 dozen goat skins. Tanners designate as a "pack" each lot of hides or skins they work through, irrespective of the quantity.

Besides salting them, there are other ways of curing hides and skins, and a large proportion is simply dried or dry-salted, the salt in the latter method being applied while the hides are moist. Dry hides, whether "flint" (i.e., simply dried) or salted, require special treatment to make them soft and pliable, without which it would be impossible to convert them into leather. Soaking in plain water is insufficient, as it would need too much time, during which there would be a great loss of gelatine. The use of chemicals and mechanical motion are required; sometimes chemicals alone will thoroughly soften the hides, but this is not often the case. Both alkalies and acids may be used for softening dried hides, and it is difficult to say which gives the better result, although the former are frequently used, mainly because treatment with acids is a comparatively recent innovation. Both kinds are effective, but the use of acids retards the loosening of the hair, although it has been proved experimentally that acid-softened hides give a slightly improved yield of leather compared with the effect of the alkaline process—a noteworthy advantage where the finished leather is to be sold by weight. The acid generally used—formic—has antiseptic properties, and can have no harmful effect on animal tissues, as is generally the case where mineral acids, especially sulphuric, are used. Sulphurous acid is also said to be a good softening agent for hides, but it is rarely used. The most satisfactory alkalies are sulphide of sodium (crystallised or concentrated) and caustic soda, and of these two, the sulphide is preferred in nine cases out of ten. The quantities used vary according to the condition of the hides, but the average is about 1 lb. of caustic soda, or 1 lb. of concentrated sulphide of sodium (65 per cent.), or 2 lb. of crystallised sulphide of sodium (30 per cent.) for every 100 gal. of water. Of formic acid, 1 lb. is sufficient for 100 gal. of water. It is possible to soften hides by these means without mechanical acid, but the time is considerably shortened by "drumming" the hides, i.e., placing them in a round or, preferably, a square tumbler fitted inside with shelves or staves (Fig. 13). The drum is rotated mechanically for a few hours, during which time the hides are thoroughly kneaded and softened by the alkali. Tanners often use a machine known as the "faller stocks" (Fig. 14), which kneads the hides very thoroughly, though somewhat drastically. The drum method is preferable, providing the hides can be suitably softened. An old method, and one that is used now by some of the small firms, is to "break over" (i.e., vigorously scrape) the hides with a curved blunt knife fitted into two wooden handles. For this manual operation, the hide is placed, flesh side up, over the tanner's beam (Fig. 15) and is then scraped with the knife.

Another old method, which has not yet disappeared, is to make use of stale soak liquors, which, although efficient for softening purposes, cause a great loss of hide substance owing to the active growth of bacteria, which are developed as a result of the water becoming foul and putrid with dirt, blood, and dissolved gelatinous matter. This method of soaking is always dangerous, apart from the great loss of gelatine, for the thin grain (hyaline layer) is liable to be eaten away in patches, a defect which greatly reduces the value of leather.

Dried hides are not only difficult to treat successfully in the different processes of making them into leather, but they are also of highly speculative value, although they are well preserved when completely dry. It sometimes happens, however, that the drying is imperfect; it may, for example, have been so rapid that the exterior of both sides is thoroughly dried before the air is able to penetrate into the centre. The result is that the interior of the hide putrefies, but there may be no indication of this until the hides are soaked and softened, when they may fall to pieces and are only saleable to glue makers. Again, the hides may be dried in the hot sun and be badly blistered, with the same result as regards their value for leather. If the hides are dried in too high a temperature, they become horny and rarely make satisfactory leather owing to the difficulty of softening them. It is estimated that quite 10 per cent. of the dried hides are improperly cured and, therefore, useless for making into satisfactory leather.

Apart from the commercial risk in buying dry hides, their import, especially from Russia and China, is a source of danger in conveying the disease of anthrax to workmen. It has been conclusively proved that dried hides are much more liable than wet-salted hides to cause infection.

So far, only one country, the United States of America, has taken steps to prevent the importation of the disease of anthrax, although most countries have issued regulations in regard to the precaution to be taken to avoid infection by anthrax in those factories where imported hides, wool, hair, and bones are treated. It would seem that the most rational method would be to disinfect the hides before they are shipped, as it certainly appears to be unwise to import any form of disease; unfortunately, the first regulations issued by the American Government proved to be impracticable, as the suggested method had the effect of lowering the quality of the hides, and making the preliminary operations troublesome. Their second scheme, consisting of baling a certain number of hides in canvas disinfected with a 0.02 per cent. solution of mercuric chloride, is more satisfactory, for, although it may not sterilise all the anthrax spores inside the bale, it should prevent them reaching other goods. This Government order only applies to hides, skins, hair, and wool coming from countries where anthrax is known to be prevalent.

The disease of anthrax is generally contracted by workers through sores or cuts in the hand; the bacilli multiply rapidly in contact with the blood, and the first sign of disease is usually shown by a red swelling or pimple in the neck. If treated at this stage by anti-anthrax serum a cure is often effected, but if treatment is delayed the disease quickly proves fatal, the patient dying in awful agony. The germs of the disease may also be swallowed and the disease develop internally, but cases of this kind are rare.

Besides the danger to workers, there is the risk of cattle being infected. The effluent from tanneries where anthrax-infected skins are treated contains millions of bacilli, and it is doubtful if the latter are sterilised even when the effluents are precipitated and aËrated before they are run into streams or municipal sewers. In any case, the sediment may be infected, and this ultimately finds its way to the land.

Until the various European Governments insist on imported hides from anthrax-infected areas being sterilised before shipment, the use of a disinfectant such as lysol or a similar cresylic compound, or bichloride of mercury, seems imperative in the first process of soaking. The use of these disinfectants would make the waste liquors fit for discharge into sewers or streams.

The English Public Health and River Pollution Acts have had a great effect in improving the hygiene of the tannery, although leather manufacturers have not welcomed them, as, in some cases, they have meant considerable expense in providing settling tanks for the treatment of waste liquors. The Public Health Act gives power to any town corporation to declare as offensive trades such businesses as tanning, hide and skin merchanting, fellmongering, tallow melting, etc., and several boroughs have taken advantage of this law. In such cases, anyone desiring to set up business in these trades must apply to the Town Council, who may or may not give their consent; in fact, a few applications to establish these businesses have lately been refused.

While the curing of wet hides with salt or in brine is more satisfactory than drying them, the use of ordinary salt is not an ideal method, as 10 per cent. brine dissolves hide substance. The recent introduction of a pure dry salt (99-98 per cent.) and of a sterilised salt for commercial purposes has to a large extent removed the objections to ordinary salt. Dry sulphate of soda is also a satisfactory cure. It may be that, as hygienic conditions are further advanced in the various industries, a suitable disinfectant will have to be used for all hides, in addition to the salt, except where the hides are sent direct to the tannery from the slaughterhouse.

The cure of hides in hot countries, especially where cheap salt is unavailable, is often unsatisfactory. A method of obviating this difficulty has been found in China, where, in one or two of the principal towns, hides and skins are preserved by freezing them in cold-storage. Although this process stiffens the hides, it is said to be fairly satisfactory if they are allowed to soften naturally before soaking them. If submitted to rough treatment before the stiffness relaxes, there is a great danger of the hide fibres being ruptured. Freezing removes the difficulty of softening which is experienced in treating dried hides, while it preserves the hide substance.

After the operation of soaking, hides and skins are ready to be treated for the removal of the hair. There are several ways of loosening the hair sheaths, but most of them consist of treating the hides in a solution of a caustic alkali. The use of a solution of common lime was practically universal until a few years ago, but nowadays sulphide of sodium, red arsenic sulphide (realgar), and caustic soda are also used, generally in admixture with the lime. Another process consists in sweating the hides in a heated room, preferably a damp cellar, where rapid decomposition of the hides soon loosens the hair. This method is rarely used in England, but a few American tanners seem to prefer it for certain classes of hides. In the American process, the hides are first soaked, and then cut in half down the back, forming what are known as sides. Dry hides are subjected to the usual mechanical operations in the faller stocks, in which they are kneaded by two large hammers (Fig. 14), or they are drummed in the tumbler (Fig. 13). After the sides are thoroughly softened and drained, they are transferred to the sweat pit, which is, preferably, a dark underground chamber. The stock requires very careful attention as the process is risky. The temperature should never exceed 75° F., otherwise the hides may be irretrievably ruined. The process may take from one to four days, according to the varying conditions of the hides and of the weather. The loss of nitrogenous matter gives rise to the development of a strong odour of ammonia, which is sometimes even too pungent for the workmen. When the hair is judged to be sufficiently loose, the sides are washed in cold water and put in the stocks again for about ten minutes, when all the hair will be removed; or the hair may be scraped off in the unhairing machine. This method is not useful for sole leather, as it causes too great a loss of gelatine, but it saves time in the production of sides intended for boot upper leather, which is usually sold by measurement (superficial area).

A dehairing process has lately been invented and patented, however, which may supersede all of the methods just described. This process consists in treating the hides with various enzymes which loosen the hair so effectively that it can be removed more easily than the hair of a limed hide. The fine, short hairs underneath are also removed, whereas by the lime method a further process is needed to get rid of these hairs. The only drawback to its use is that the inventor has not yet been able to produce a material cheap enough to place on the market, but as soon as this difficulty is overcome the enzyme method may become fairly general. Neither the hair nor the gelatine of the hide can be damaged by this method.

The usual method of liming is carried out in brick pits of square or rectangular shape with a sloping front on which the hides or skins can be piled to drain (Fig. 16). There is a great variation in the quality of lime, and in all cases it should be tested for the available percentage of caustic lime. A good sample should contain between 70 and 80 per cent. of pure lime. Buxton lime, which can be obtained in powdered form, is particularly suitable for the tannery. The ordinary lime is preferable to the chalk lime, as it is usually stronger, though it sometimes contains more impurities. Gas lime is the poorest of all. Lime should be stored in a dark place, otherwise the outside of the heap carbonates quickly, forming chalk (Ca O + CO2 = Ca CO3) which is of no use for the liming process.

To prepare the lime for the pits it is slaked (i.e., formed into a paste with water. All the lumps should be reduced to paste in order to avoid lime burns, which are caused by direct contact of the hides with pieces of unslaked lime. A certain quantity of the paste is then added to the water or old lime liquor in the pit, and the liquor is well plunged up to hasten solution and diffusion of the lime. A long wooden pole, with a flat block of wood attached, is used for this purpose and also for pressing down the hides under the surface of the liquor.

Two methods of liming are in vogue: (1) the single-pit system, and (2) the three-pit system; but the latter is the better method, as it is more easily controlled, and causes less loss of gelatine than the former. In this system the liquor is strengthened with fresh lime for each pack of skins. Its great fault is that the pit is only cleared out at long intervals in order to take advantage of the mellowness of used lime liquors; hence, there is frequently large accumulation of insoluble limestone and other sediment from the lime, in addition to a quantity of dissolved gelatine, which rapidly accumulates putrefactive bacteria. When the pit is cleared out the process of liming is disturbed for a time, as fresh lime liquors are not beneficial to hides and skins, and the loosening of the hair is delayed. On the other hand, the three-pit system permits liquors of uniform strength, and the process is continued without interruption. Each new pack is first placed in the oldest of the three liquors, which is then cleared out, and a new liquor prepared. From the weakest pit the hides pass to a stronger liquor, and the process is finished in the third pit, which should contain a new lime liquor. The mellow liquors, being charged with bacteria, facilitate the loosening of the hair, while the third liquor, consisting of fresh lime, serves to swell the fibres of the hide, by means of which the flesh is more effectually removed. The lime also forms a soap with the natural grease of the hide; this grease can therefore be removed. In some cases, however, especially in the cattle fed up for Christmas, the hides contain a larger quantity of fat than the alkali of the lime liquor can convert into a soap, and the surplus grease is frequently seen in the finished leather, as it is difficult to remove in later processes. A solution of hyposulphite of soda, or lactic acid, given just before the process of tanning is said to remove the grease, although a slight loss results in the case of those leathers sold by weight. The objection to natural grease in leather can be understood where the latter is intended for colours, but in the case of sole leather it ought not to be a disadvantage, yet, owing merely to the darker appearance of the leather where the grease reaches the grain, its selling value is reduced by 2d. or 3d. per lb. The strange part is that the grain of this sole leather, when made into boots, is buffed on an emery wheel, then sometimes coloured with a paint, and finally sold in boots at the same price as leather free from grease and regular in colour.

The liming process in pits takes from six days to a month, according to the character of the leather required. Light calf skins may be ready for unhairing within a week, while hides intended to be finished for "raw hide leather" may be left in the pits quite a month, the object being to distend and harden the fibres. Lamb skins intended for parchment, and small calf skins for vellum, are also subjected to prolonged liming. Between these extremes, there are several stages in the process which have varying effects on the character of the finished leather. In fact, it is a tanner's dictum that leather is made or marred in the lime liquor, though this, of course, only applies to a certain extent. Generally, however, the heavier the hides, the longer the liming required. Fortunately, the limited solubility of the lime in water affords a wide margin of safety in working, and the only danger to guard against is the too prolonged use of old liquors, which are readily detected by the strong odour of ammonia. One important property of lime is its lower solubility in hot than in cold water.

Lime by itself does not readily attack the hair bulbs, and the slowness of the process has led to the introduction of other chemicals, generally for use in conjunction with lime. The principal of these are sulphide of sodium and red arsenic. Mixtures of sulphide of sodium and lime, or red arsenic and lime are now largely used, the former for hides, calf, and sheep skins, and the latter for goat and kid skins. Both sulphide of sodium and arsenic dissolve keratinous matters (horns, hair, etc.) and workmen should, therefore, be provided with rubber gloves to prevent the loss of their finger nails. Sulphides naturally lower the commercial value of the hair removed and, if used alone, destroy it. In admixture, however, the hair has some value, although it is not so good as that removed by the use of pure lime. Against this, however, there is a great saving of time and less loss of hide substance and, therefore, increased weight of leather. Sulphide of sodium is prepared in crystallised or concentrated form; the former, about 30 per cent. strength, is preferred in Great Britain, while the latter—65 per cent. strength—is prepared for export, the main object being to save the cost of transit of 35 per cent. of water. About thirty different sulphide salts may be used, but the sodium and arsenic disulphides are the best, as it has been shown that the most rapid loosening of the hair occurs where the quantities of sulphur and alkali are nearly the same. There are two arsenic salts used in the trade, namely, realgar, or red sulphide of arsenic (As2 S2) and orpiment, or the yellow sulphide (As2 S3), but the former is often preferred as it is said to give better results than the latter. In practice, the proportion of arsenic used is 1 part in 20 parts of lime, although it naturally varies a little according to the class of skin under treatment. Sulphide of sodium is used in the proportion of 1 part to 10 of lime, or, if concentrated sulphide be used, 1 in 20. The quantities of lime, or lime and sulphide, used are estimated on the weight of the raw hides. For hides intended for sole leather, 5 per cent. of lime on the weight of hides is ample, while a little more may be used for hides intended for dressing leather (i.e., leather which has to be dressed or finished with a certain degree of flexibility for bags, boot uppers, etc.). When a mixture of lime and sulphide is used, 3 per cent. and 0.3 per cent. respectively is a satisfactory quantity. The action of this mixture on hides is complex and has not yet been definitely ascertained, but it is thought that the calcium sulphydrate formed by the chemical reaction between sulphide of sodium and calcium hydrate (slaked lime) is the active principle.

In the pit method of liming, it is essential that the liquors be frequently plunged, while the hides should be taken out ("hauled"), piled to drain for a few hours, and put back again ("set"), or transferred to another pit. Although lime is more soluble in cold than in warm water, it is found in practice that the process may be stopped or considerably retarded in very cold weather, and the activity of the liquors is increased by the application of waste steam (conveyed through iron pipes from the boiler).

Sulphide of sodium and lime are sometimes made into a thin paste, which is applied to the hair side of hides and skins with a mop or fibre brush. The hides are then folded down the back with the flesh sides out; other hides are similarly treated and placed in a pile. This saves a great amount of labour in pitting, and, if the paste is fairly strong, consisting of 2 to 2-1/2 per cent. sulphide, the hair can be removed after a few hours.

With so many depilatories available, it is not surprising that several patents have been granted and numerous suggestions made with the object of trying to improve on the old process of liming. While there may be some objections to lime, it has a few advantages which are lacking in other depilatories. These advantages are not perfectly understood theoretically, but the tanner recognises them in practice. Hence, there are very few tanneries where lime is not used at all, and the only progress that seems to have been made in the process of liming consists in the admixture of sulphide of sodium or arsenic to hasten the process, reduce the loss of gelatine, and, in the case of arsenic, to improve the fineness of the grain of skins for boot upper and glove leathers.

One patented method consisted in forming the calcium hydrate within the hide by treating it with a 1 per cent. solution of caustic soda and then with a 1-1/2 per cent. solution of calcium chloride, the reaction of these two chemicals forming calcium hydrate (lime) and sodium chloride (salt). This method, however, does not loosen the hair at all and has to be supplemented by soaking the hides in putrid water. It is a good method of liming hides or skins dressed in the hair, as it opens up the fibres without weakening the hair roots and prepares the hides in a suitable condition for tanning.

Another method consists in mixing a small quantity of soda ash with the lime, thereby hastening the process by increasing the alkalinity of the liquor.

A somewhat complicated method was introduced a few years ago, but, although it seemed advantageous from a chemical point of view, it has not proved successful in practice so far as is known, probably because of its expense. In consisted of four distinct processes. The hides were first mopped on the hair side with a thin paste of lime and arsenic, and dehaired after twenty-four hours. In the second process, they were treated in a drum for twenty-four hours with a solution of sodium sulphide, they were then drummed for twenty-four hours in a solution of hyposulphite of soda, and finally placed in a vat or pit containing a solution of lime and a little arsenic for two to five days. After washing, etc., they were ready for tanning. The sulphide of sodium swelled the hides or skins by distending the fibres, and the natural fat is converted into a soluble soap. The hyposulphite arrests the action of the sulphide and acts as an antiseptic.

In modern yards it is a growing practice to use mechanical power to keep the hides in motion, instead of handling them. The hides are attached to poles joined to a strong cross beam, which, in its turn, is connected by stout iron rods with the main pullies and shafting. The installation is expensive, but it saves an enormous amount of manual labour and time, while ensuring uniform treatment. This method is not so much used for liming as for the tanning process.

After loosening the hair and opening up the fibres, the next operation is dehairing or depilation, or, as it is generally described in the trade, "unhairing." The hair must slip quite easily before beginning this operation, otherwise a number of them will be left in the hide and will be difficult, or almost impossible, to remove later on if the hides are being made into sole leather. These hairs present an unsightly appearance and lower the value of the leather. Depilation may be done by hand or machine; but the latter method is rapidly superseding the former, as it is in nearly every other process of leather manufacture.

In the manual process, the hair is removed by scraping it off in a downward direction with a blunt, convex-shaped knife, fitted into two wooden handles (Fig. 17), the hides being placed on a sloping convex beam (Fig. 15) supported by a trestle. A series of grooves under the beam permits it to be placed at any angle. The beam (different from that used by curriers) may be of wood, iron, steel, or zinc-covered wood.

There are several types of unhairing machines, of which the Leidgen more nearly approaches hand work than any other. The skins are placed on a soft bed of felt, and the working roller, fitted with spiral knives, is brought into contact with the hide and scrapes off the hair.

The type of machine often used, however, is shown in Figure 18; the working part is a long spindle fitted with helical knives. The advantages of this machine are its large output and its use for other operations by simply changing the working roller. The blades must be blunt for dehairing, but sharpened blades are needed for fleshing.

If hides intended for sole leather are being dehaired, the short hairs which are not removed by the dehairing knife are carefully scraped off with a sharp knife. Other kinds of hides and skins are freed from short hairs in a later operation.

When the hides are dehaired, they are sometimes submitted at once to the next operation of fleshing, which, as its name implies, consists in removing loose flesh and fat from the "flesh" side, that is, the side near the carcase. The extent to which this operation is carried out depends on the quality of the finished leather. Naturally, the more flesh left on the greater the weight, particularly as loose flesh will absorb a large quantity of tannin, and, unfortunately, of adulterants which are frequently used for weighting common leathers. The flesh ought to be removed in all cases, for the loose flesh forms very poor and spongy leather. Where hides and skins are tanned and then dried for sale to leather dressers and finishers, there is often the tendency to leave far too much loose flesh on them, with the object of producing as much weight of leather as possible. From the point of view of economy, this is a mistake, for the loose flesh must be removed during the dressing process, whereas, if it had been taken off at first, both material and time would have been saved in the process of tanning.

If the fleshing is not done directly after dehairing, the hides or skins should be placed in a weak lime liquor, and this method is to be recommended. The great point to be observed is to keep the limed hides, both before and after dehairing, away from contact with the air, as the chemical action of the carbonic acid on lime results in the formation of chalk, which tends to harden the hides and to roughen the grain, so that it is likely to be scratched in later operations. Where the hides are intended for sole leather, and not treated with an acid before entering the tanning liquors, the presence of chalk would lead to an uneven colouring of the leather.

Fig. 19

FLESHING KNIFE