The skins of various animals, in their fresh state, are flexible, tough, and elastic, and appear to be admirably adapted to the purposes of clothing. But in drying they become hard and horny, and, on exposure to moisture, putrid. The art of restoring the supple qualities to skins, and rendering them durable, appears to have been discovered at an early period of man's history; and the word leather, from the Saxon lith, lithe, or lither, indicates the quality of suppleness.

Leather is formed by the chemical union of the dermis, corium, cutis, or true skin of an animal, with an astringent vegetable principle, known as tannin or tannic acid. The word tan, from the French tanner, to tan, appears to be derived from the low Latin tamere. Leather may, however, be prepared by impregnating the skin with alum, oil, or grease.

In the animal hide or skin, the outer part, which is covered with hair or wool, is called the epidermis or cuticle, below which is the reticulated tissue, and then, in contact with the flesh, is the dermis, or true skin, which is the only part which admits of being tanned. It varies in thickness in different parts; the mane, the back, and the rump, being thicker than the belly. The skin is converted into gelatine, or glue, by the action of boiling water.

Varieties of Leather.—The leather tanned in England is generally divided into three kinds, namely, hides, kips, and skins, and these yield different varieties of leather, such as butts and backs, which are made of the stoutest and heaviest ox-hides. Fig. I will show how the butt is formed by cutting off the cheeks, the shoulder, and a strip of the belly on each side, the skin of the head having been previously removed for the use of the glue-maker. For backs, the cheeks and belly are cut off, but the shoulder remains. Hides are similar to butts with the bellies on, and are made out of cow-

When hides are tanned leather, called crop hides. Skins

The stoutest leather is made from butts or backs. Buff leather was formerly made from the hide of the buffalo, but it is now furnished by cow-hide, and is used chiefly for soldiers' belts. Bull-hide is thicker than cow-hide, while that of the bullock is intermediate. Calf-skin supplies the great demand for the upper part of boots and shoes. Sheepskins form a thin cheap leather; lamb-skins are used for gloves; goat and kid skins form a light leather of fine quality; deer and antelope are usually shawmed, or dressed in oil; horse-hide is prepared for harness-work, &c., and this, with seat-skin, is used for making enamelled leather; dogskin makes a thin tough leather, but most of the gloves sold as dog-skin are made of lamb-skin. Hog-skin makes a thin porous leather, and is used for covering the seats of saddles. There is a large import trade in skins. The great demand for leather for the best gloves is supplied by lamb-skins from Italy, Spain, the south of France, and other parts, where, in consequence of the lamb being killed earlier than with us, the skin is small, fine, and thin, and is used instead of kid; but it is neither so strong nor so glossy. The skins of lambs that die soon after their birth are sometimes dressed with the wool, and are used for lining gloves and shoes. The best kid-skins are from the south of France; they are also imported from Germany, Switzerland, Italy, and Ireland. It is said that as soon as the kid begins to feed on herbage, the skin suffers in fineness and delicacy, and is no longer suitable for the best gloves. The best morocco leather is made from Swiss goat-skins, another kind is from Mogador and East Indian goat-skins, which are often made into black morocco, known as "Black Spanish leather," from the circumstance of our first supplies having been obtained from Spain. The leather from the Cape sheep-skin is nearly equal to morocco. Hippopotamus hides are imported from South Africa, and when tanned with oak-bark, they make an extremely thick and compact leather.

Tanning Materials.—The vegetable substances used in tanning have of late years become almost as numerous as the varieties of hides and skins on which they are employed. The active vegetable principle tannin varies somewhat according to the source from which it is derived; but it is always marked by an astringent taste, a bluish-black, or dark green precipitate, in aqueous solutions, by admixture with a solution of one of the salts of peroxide of iron; while, with a solution of gelatine, it gives a dirty white or brown precipitate. A cold aqueous solution of tannin, mixed in certain proportions with one of gelatine in the form of glue, size, or isinglass, forms a substance which is known as tanino-gelatine, which may be formed by the application of heat into a viscid elastic mass, resembling India-rubber. By the action of ether, containing a little water, on gallnuts, pure tannin may be procured. The ethereal solution separates by repose into two layers, the lower one, which is of an amber colour, being a solution of tannin in water; while the upper layer contains gallic acid, mixed with other substances. On gently evaporating the aqueous solution, nearly pure tannin is procured, to the extent of from 35 to 40 per cent., from galls. Obtained in this way, it is a shining, porous, uncrystallizable mass; it is soluble in water, and then exerts the properties of an acid. By exposure to air it absorbs oxygen, and gives off carbonic acid; two new products, gallic acid and ellagic acid, being formed at the expense of the tannin, the latter being insoluble. Tannin may be precipitated from its solutions by sulphuric acid and some other acids; by boiling the precipitate with sulphuric acid for a few minutes in a dilute solution of the same acid, gallic acid is formed, and crystallizes in cooling. Gallic acid exists in gall-nuts, sumach, vallonc, tea, and other substances, and probably arises from the decomposition of tannin. It does not combine with gelatine, and is, therefore, useless in tanning. Some tanners, however, imagine the gallic acid of the waste liquor to be useful in swelling or raising the hides, preparatory to removing them to a stronger liquor. It is important to the tanner to understand the circumstances under which tannin is converted into gallic acid; they are numerous and somewhat complicated, and their investigation belongs to the scientific chemist, to whom the manufacturer already owes so many obligations.

During a long period the principal tanning material in this country has been oak-bark. That which is stripped in the spring is the most esteemed, for it then contains a larger quantity of tannin than that stripped in autumn, and this more than the bark stripped in winter. The best bark is obtained in a warm spring, from coppice trees about 12 years of age. Oak-bark contains from 5½ to 6½ of tannin, which is contained in the inner white layers next the alburnum, as in the case of other astringent barks. The tannin of bark is probably not identical with that of galls, as it does not yield pyro-gallic acid, when subjected to destructive distillation. From 4 to 6 lbs. of oak-bark are required for every pound of leather. A load of oak-bark, consisting of 45 cwt., delivered in London, varies from L16 to L16, 10s. After the stripping, the bark is stacked to dry. Should the season be rainy a portion of the tannin may be washed out, and the bark be thus deteriorated. There is no doubt that the peculiar excellence of the sole leather of England is due in great measure to the superior oak-bark which we possess. Oak-bark imparts firmness and solidity to leather, while other sorts give softness; thus the peculiar softness of French curried leather is referred to the bark of the evergreen oak, with which the better kinds are tanned, while the other tanning materials next to be named give each its peculiar quality with respect to colour, scent, toughness, or the power of resisting moisture and decay.

The other tanning materials, used chiefly for fancy leathers, are as follows:—Sumach, consisting of the young branches and powder of the leaves of Rhus Cotinus, Venus sumach, or the wild olive, and Rhus Coriaria. Sumach varies in its amount of tannin from 16½ per cent. in Malaga and Sicilian specimens, to 10 and 5 in Virginia and Carolina sumach. The solution is liable to fermentation. Dici, or dici-dici, is the pod of a South American shrub, Caesalpinia Coriaria. The pod is dark-brown, about 3 inches long, and curled up as if by heat. It is rich in tannin, the whole of which is found in the rind below the epidermis. Vallonea, consisting of the acorn cups of Quercus Hyglops, or prickly-cupped oak, growing in the Morea. A smaller kind, called cornota, containing a larger proportion of tannin, is for the most part used by the silk-dyers. About 2 lbs. of vallonc are required for making 1 lb. of leather. Vallonea and oak-bark may be mixed together with good effect. Catechu, cutch, Terra japonica, or terra, are the inspissated aqueous extracts of the bark, wood, and leaves of the Acacia Catechu, and Uncaria gambier. The two varieties are known in commerce as catechu, or gambier, and cutch; that from Bombay is richer in tannin than that from Bengal. Myrobalan is a name given to the fruit of several East India trees; the husk, being the portion valuable to the tanner, is separated by bruising the nut which it incloses. Mimosa or Wattle-bark is furnished by different species of Mimosa growing in Australia and New Zealand. Cork-tree bark is the inner bark of the cork oak, the outer or dead bark being the well-known substance, cork. It is obtained from Corsica, Spain, and a few other countries, and contains twice as much tannin as average oak-bark. Larch-bark is sometimes used for tanning sheep-skins, and Willow-bark for kid and lamb skins. The last named bark is used in making Russia leather, but its peculiar odour is given by means of the oil of birch-tree bark.

In addition to the tannin contained in the above substances, there are mucilaginous, colouring, and other matters which have an influence on the kind of leather produced. The tannin itself may also vary in different materials; thus, catechu and divi give a more porous leather than oak-bark or vallonc, while larch-bark gives a very inferior leather to that prepared from oak-bark. The colouring matter in some excellent tanning materials prevents their use, since it is the custom to sell both upper and sole leathers of a yellowish-tawny colour, and anything which interfered with the production of this tint would be objected to; thus, catechu and cutch would be among the cheapest of tanning materials, were it not that they impart to the leather a reddish-brown colour, which would in no way interfere with the dressing or currying.

The tanner frequently judges of the strength of his infusions of bark, technically called oozz, by means of a kind of hydrometer called a barkometer. It is graduated to the standard of pure water, and when placed in a specimen of ooze, the strength of the latter is judged of by the position of the stem above or below the water-mark. But as a bark or other tanning material may contain several soluble substances besides tannin, the barkometer obviously cannot be relied on. Some tanners judge of the strength of ooze by the taste, the amount of astrigency determining the strength. The usual test for tannin is a solution of glue or isinglass, which being mixed with a known weight of a solution of tanning material, a precipitate of tanno-gelatine is produced which is filtered, dried, and weighed: the proportion of tannin is thus ascertained. As, however, some kinds of tannin produce larger precipitates of gelatine than other kinds, and as the composition of tanno-gelatine varies with the strength both of the solution of gelatine and of tannin, this method is not reliable. Sulphate of quinine is said to afford a better test; a solution thereof, acidulated with a few drops of sulphuric acid, will, it is said, precipitate tannin completely from the solution. A good method of testing the value of tanning material is to digest a piece of dry prepared hide or skin in a known quantity of the infusion, until the whole of the tannin and other matters be separated. The skin is then taken out, slightly washed, dried, and weighed, when the increase of weight is supposed to be the weight of tannin and of the other matters required.

Tanning of Thick Leather.—The first operation to which the hides and skins are subjected is depilation, which removes not only the hair, but also the scarf-skin. This is effected variously in different countries. In England the most common plan is to throw the hide or skin into a strong watery ley of slaked lime, with lime in excess. Here, in a few days, more or less according to the proportion of lime present, the hair is easily detached, the hair-sheath having been dissolved; the scarf-skin with the hair are then scraped off upon a sloping rest, with a species of knife with two handles. The lime has also combined with the fat of the hide to form a calcareous soap, to dissolve which, and the excess of lime, it is well washed, sometimes in a running stream. The hide is fleshed, or deprived of the loose or extraneous flesh or cellular tissue; and if butts are to be made, the head, shoulder, and bellies are cut off, as Leather already noticed. The central part, or butt, weights about two-thirds of the whole leather. The hair was formerly taken off by making a sour liquor from fermented vegetable matter, in which the hide lay for several days; they were also smoked in a damp state for the same purpose; but both those methods are now abandoned. They are still sometimes sweated, that is, they are laid in heaps, and kept wet and warm; but in America the sweating is performed cold; the hides are hung up wet in a damp underground cellar, and are kept moist for ten days or a fortnight, a plan which is still adopted in this country for skins. In either of the three last processes, incipient putrefaction takes place sooner or later, when the hair and scarf-skin are easily removed; but the fatty matter remains, and in some cases prevents the hide from taking the tan. The tanning either follows at once, or is preceded by what is called abating or grainering. For this process, a quantity of pigeon's dung is dissolved in water. In this mixture the hides are steeped for a week or ten days, with occasional removals and strikings. The theory of this process is obscure; but it has been explained on the supposition that the uric acid of the dung removes the excess of lime, and that the ammonia generated by the putrefaction of the mixture tends to form an ammoniacal soap with any remaining fat of the hide; but as the gelatine of the hide exists in two states,—one, the principal, hard, or fibrous portion, and the other (which is more soluble) contained between the fibres, and more affected by agents and putrefaction—this softer portion is removed by grainering, and the leather, when tanned, is light and porous, and more readily permeable to water.

Some tanners are anxious that their leather should look thick when completed. To "raise" the hide, they use a solution of sulphuric acid, containing $\frac{1}{3}$ part of acid; in this the hides remain ten or twelve hours, when they are found to be thickened, or to have substance; but as nothing is added to the gelatine by the process, it is only the appearance which is altered, and no difference of thickness is found in the leather after it has been under the shoemaker's hammer.

The hide or skin thus prepared is ready for tanning. It was formerly the practice in England, as it now is on the Continent, to tan by the process of stratification, for which purpose a bed of bark is made upon the bottom of the pit; upon this is laid the hide, then bark, then a hide, and so on, until the pit is full; water is sometimes pumped in, and the pit left for some months; it is then emptied, and the same hides returned with fresh bark and water for a few months longer; this is repeated again and again, until the tanning is completed; the time varying from one to four years for heavy leather.

About the end of the eighteenth century, Seguin professed to give a theory of tanning. He showed that astringent solutions contained gallic acid, which precipitated sulphate of iron black, but did not precipitate gelatine; whereas the tannin present threw down gelatine as well as sulphate of iron; and from this he deduced that leather was a compound of gelatine and tannin. Upon this he founded a new process. He recommended that the hides should be subjected to the action of solutions of tannin, made by pumping water successively upon the vegetable used, contained in latches or spenders, until it arrived at as great a degree of strength as the series of spenders permitted. In this way he was continually throwing away some bark as expended, and replacing it with fresh, which was next to be the strongest tap.

This is the plan generally followed in England; but in practice it is varied, some using ground bark only, others Terra japonica, vallonea, or divi-divi, or mixtures of two or more; some using steam to facilitate the solution, others steaming only the backward latches; and some using only cold water. In some yards clean water only is used to extract the soluble matter, while in others the oozes, exhausted as much as it can be by the hides, is made to perform the office instead of water. Every tanner has also his own particular strength of liquor to work at, the strongest being about sixty degrees, while others do not go beyond ten degrees. It is these variations which cause so great a variety among the samples of leather in the market.

This improvement of Seguin was of importance in shortening the period of tanning to about half of that previously occupied. The principal difficulty experienced in its use occurs in the estimation of the real quantity of tanning material actually in solution. He proposed the use of a solution of gelatine, isinglass, or glue, which was to be dropped into the fluid as a test of the presence of the tannin. In the hands of an experienced chemist this is a tolerable means of arriving at the quantity; but it proved too difficult for the tanner of the day. He therefore judges by the astringent taste of the solution, and its darkness of colour; or depends upon its strength from a certain weight of bark, &c., which may have been used. The use of the barkometer has been already referred to.

In trying the quantity of tannin by Seguin's process, that is, by precipitating it with the solution of gelatine, 480 grains of the bark in coarse powder should be acted on by half a pint of boiling water. The mixture should be frequently stirred, and suffered to stand twenty-four hours; the fluid should then be strained through a linen cloth, and mixed with an equal quantity of solution of gelatine, made by dissolving glue, jelly, or isinglass, in hot water, in the proportion of a dram of glue or isinglass, or six table-spoonfuls of jelly, to a pint of water. The precipitate should be collected by passing the mixture of the solution and infusion through folds of blotting-paper, and the paper exposed to the air till its contents are quite dry. Every 100 grains of precipitate contains 40 grains of tannin nearly.

When the hide or butt has been brought from the beamyard, it is introduced into a poor and milky liquor, in which it is handled for four or five days; that is, it is lifted by hooks from the pit, laid with other hides in a heap on the side, where it is allowed to drain, and is then returned into the pit. The lime is intended to be taken out here by the gallic and acetic acids of the poor ooze, as it is found in practice that the presence of lime tends to darken the colour of the future leather, an effect produced by all alkalies and alkaline earths. The hide is next successively handled into and out of all the hammers, increasing in strength; and in this way at length, having after some months got to the strongest handler, it is found to be stained through, though not tanned, when it is removed to the pits which contain still stronger liquors; these it successively passes through, being handled at longer intervals. Upon arriving at the end of this series, the hides are laid away in a pit called a layer, where they are interstratified with powdered bark or vallonia; the pit is then filled up with very strong ooze. When the process is deemed complete, each hide, on being taken out, will be found to be converted into leather; and a portion of its gelatine which has been dissolved from its interior is, by combination with a portion of tannin from the strong solution, deposited upon its surfaces, where it is found in the form of a yellow deposit, technically known as bloom, or pitching, which disguises the under colour of the leather, just as if it were covered with yellow paint. This prejudice says, must be on its surface, or it is not salable; but it is so much quality and weight lost to the consumer, as he pays for it on the outside of his leather, to be scraped off by the shoemaker in the operation of buffing; and the leather is so much the worse, as, if it had remained incorporated with the leather, this would not have been so porous, or so permeable to water. The health of the wearer of the shoe is perhaps sacrificed by wet feet, occasioned by the desire of his shoemaker to see a yellow paste on his leather, which in work he scrapes off with a piece of glass. The theory of the formation of the bloom is this. As soon as ooze has penetrated into a hide, it loses its tanning material, but by capillary attraction is detained; this exhausted ooze acts by maceration on the finer and more soluble interstitial gelatine, and dissolves it. In handling, about one-twelfth of this flows out; the remaining eleven-twelfths accompany the hide into the next stronger solution, of which only one-twelfth is absorbed directly, and a small portion is slowly exchanged by endosmosis and exosmosis. The small portion of strong solution which passes into the pores of the hide contributes to tan the hard fibrous portions not dissolved; and the small portion of weak solution passing out of the hide by exosmosis, gives up its dissolved gelatine to the tan of the stronger solution outside, to form tannate of gelatine, which partly adheres to the surface as bloom, and partly falls to the bottom of the pit as pitching. It is to be hoped that such an exposition will tend to lead to the adoption of some system of tanning in which the exhausted ooze may be so quickly removed by pressure as not to allow it to dissolve the finer and better portions of the skin. Some years since, Mr Spilsbury endeavoured to introduce a new principle in tanning, by which some part of this action should be prevented, by bringing strong ooze at once into contact with the inside of the hide. He obtained a patent for a plan of tanning by infiltration. He fastened two hides in clamps, so that the frame represented four sides of a box, and the two hides two sides. By filling this box with strong tanning ooze, and forcing it through the pores of the hides by the pressure of a column of the fluid, he expected to tan them promptly and well; but he was not aware that a large excess of tannin dissolves gelatine, and thus tannate of gelatine was found on the outside of his box in long masses of slime, while the leather had lost as much in weight, was porous, and was tanned very much more in the thin than the thicker parts, as the fluid always passed through the easiest channel.

Many other inconveniences attending the process caused it to be abandoned; but the erroneous principle upon which it was founded not having been made public, three other patentees followed in the same track. Mr Drake of Bedminster sewed hides together, so as to form a bag, which he placed inside a hollow frame-work of wood to support the ooz, and then filled it with ooze. Mr William Cox of Bedminster sewed up a hide in the same position as it was on the animal's back, laced a canvas support round, and then filled it with ooze; and Mr Chaplin sewed his hide into a bag, filled it with ooze, but laid it in a reclining position, turning it periodically.

Seguin's process of tanning by solutions, although a great improvement upon the old method, is still tedious and expensive. Where warm oozes are used, it requires six or seven months for sole-leather; where cold oozes are in use, it extends to twelve months; consequently the tanner can turn his money only once a year; he must have capital enough to pay for twelve months' hides, bark, &c., labour, and contingent expenses, besides keeping a stock of leather; and when his capital has been turned at the end of twelve or more months, it must pay him, in one single profit, the interest, &c., of twelve months. This has confined the trade to a few wealthy individuals, who look upon tanning as an investment for capital rather than as a business which might be improved by science. Hence tanning has been more stationary than any other manufacture, and the few improvements which have been made in it have not been made by tanners. Another patent has occupied considerable attention. It is founded upon the principle adopted in washing a sponge. The old tanner takes his spenge (the hide) full, or nearly so, out of one ooze, and inserts it nearly full into the next. The patentees of the roller and belt system squeeze, by a simple and self-feeding press, their hide, before they drop it into the fresh ooze; and this simple modification would seem to promise well for the improvement of the art of tanning. Messrs Herapath and Cox of Bristol, the patentees, say that, to tan 100 butts per week, they erect in a tanyard, capable of tanning 50 per week, six or eight large pairs of rollers, one pair over each pit. The lower roller is 30 inches in diameter, and is covered with horse-hair cloth; the top one 18 inches, with levers for weights, covered with woollen cloth. For each pair of rollers there are from 50 to 100 hides, connected together head to head and tail to tail, each by about four strings. Now the first butt or hide is inserted between the rollers loaded to the proper pressure; and upon turning the bottom roller (which requires very little force, as it is a slow motion), all parts of the butt are pressed as they are pulled through by the rollers; the next comes in order by the assistance of the strings; and so on, until the whole of the hides in the belt have been pressed, and deposited in the fluid on the other side of the pit. By a detent the motion is now reversed, when the belt is again pressed, and returned to its original position for a fresh supply of ooze (see fig. 2). This simple plan brings strong ooze so frequently into the interspaces of the hide, that the centre of a stout butt is not only stained through, but tanned, in between one and two months; calfskins and kips are tanned in from twenty to thirty days; and the liquors are so rapidly exhausted, that they are reduced from 45° to nothing in thirty-six days, losing at first more than 2° per day; and the shortness of this exposure to the air prevents much of the tannin from being decomposed. It was stated at the time when this patent was taken out, that at Nailsea, near Bristol, 100 butts per week were tanned, with six latches, six rolling pits, twenty-four handlers for the offal, and six layers; one horse-power driving the rollers, and two boys managing them. The following were given to us as the results produced in the first yard which was put entirely on the patent plan, as compared with those of the same yard on the old plan:—Double the work was done, and half the capital drawn out as useless. The saving on bark, labour, and general cost of manufacture was 1½d. per lb. The increase in the weight of butt leather was as 34 lb. to 28 lb.; 464 lbs. of leather being produced from a 60 lb. wet salted hide. The butts were sent to market within four months from the time the hides were delivered to the yard. The profits from quick return, great weight, and small expense, were eight times as great as on the old plan, at similar prices of hides, bark, and leather. The leather was also said to be more elastic, and more impervious to wet, than any other that is made. Notwithstanding all these brilliant results, the plan seems to have failed. An extended experience with the new method seemed to prove that the leather was more brittle, and in other respects inferior to that produced by the old method, which still continues in operation at most tanneries.

We must notice Berlier's method of making leather by means of metallic or earthy substances. The hides are washed, unhaired, and swelled as before, when they are immersed in a solution of sub-sulphate of peroxide of iron, or sulphuric acid, with excess of the peroxide. The solution Leather may be prepared as follows:—2 cwt. of bruised sulphate of iron are dissolved in 15 gallons of boiling water, in a copper boiler. The solution is run off into a shallow vessel of the capacity of 44 gallons, then 44 lb. of sulphuric acid, sp. gr. 1.848, are stirred in, together with 44 lb. of black oxide of manganese in powder; but the latter must be added gradually, the whole being stirred up so long as gas is discharged, and afterwards, at intervals, until the solution is cold. It may then be diluted with water to the required strength. By digesting hides and skins in this liquor, they become impregnated with an insoluble sub-sulphate of peroxide of iron, while there remains in the liquor free sulphuric acid, sulphate of manganese, and a small quantity of proto-sulphate of iron. It is stated that hides in the course of six or eight days, and skins in three or four days, become converted into leather, which is as impartscent and as impermeable to water, as leather tanned in the usual manner.

Splitting.—In the preparation of certain kinds of leather, the hides, after immersion in a weak ooze for from ten to fourteen days, are split into two portions, after which the halves are tanned separately. The upper, or grain half, is used for covering carriages, and the flesh half for enamelling. The principle of the machine used in the splitting will be understood by referring to fig. 3, in which D represents a mahogany drum, 4 feet in diameter, and about 6 feet in length: the tail end of the hide or skin is fixed into a slot in the drum at A, by means of wooden wedges; B is a steel knife of the length of the cylinder, attached by means of screws S, S' to the bottom of a cast-iron carriage C, C'. Rapid motion is given to the carriage by means of a crank, by which the knife is made to vibrate rapidly backwards and forwards in a plane parallel to the axis A of the drum. The hide h is kept flat to the cylinder by means of a thin plate of steel G, called a governor, placed in front of the knife, and, being pressed down by a weighted lever, smooths out the wrinkles. As the hide h is thus cut, one-half f, which is the split flesh side, passes over the knife, while the other half, consisting of the split grain side g, adheres to the drum. The thickness of the split may be regulated by means of a screw L at each end of the drum, which screw, acting upon a lever LL, raises or depresses the axis of the cylinder, and thus diminishes or increases the thickness of the split grain side of the hide.

Currying.—The skin of leather as it leaves the tannery, is a comparatively rough article, and requires the manipulations of the currier in order to fit it for the shoemaker, the coach-maker, the harness-maker, and other numerous trades in which leather is employed. Let us suppose that a tanned calf-skin is to be prepared for use. It is first made pliable by soaking in water, after which it is shaved on the flesh side, whereby the loose rough portions are removed, and a tolerably smooth surface is produced. This operation is carried on at a beam or strong frame of wood, supporting a stout plank faced with lignum vitae, and set vertically, or nearly so. The knife (fig. 4) is a double-edged rectangular blade, about 12 inches by 5 inches, with a straight handle at one end, and a cross handle at the other, in the plane of the blade. The edges of this knife are first made very keen, and are then turned over so as to form a wire edge by means of the thicker of the two straight steel tools shown in fig. 5, which wire edge is preserved by drawing the thinner steel tool along the interior angle of the wire edge from time to time as required, for which purpose the man holds this smaller tool between his fingers, together with the beam-knife. The skin being thrown over the plank, the man presses his body against it, and leaning over the top, holds the knife by its two handles, almost perpendicularly to the leather, and proceeds to shave it; shifting it from time to time, so as to bring all the parts under the action of the knife, and frequently passing a fold between his fingers to test the progress of his work. The skin is then placed in cold water, and removed to a mahogany or stone table, to which the wet flesh side adheres, and is worked with a tool called a stretching-iron, or slicker S (fig. 5), consisting of a flat rectangular piece of iron, copper, or smooth hard stone, fixed in a handle. With this tool, a man scrapes the surface of the skin, exerting a strong pressure with both hands, and dashing water upon it from time to time, by which means lumps and inequalities are made to disappear, the leather is equalized and extended, and the bloom is brought to the surface. The superfluous moisture is now slicked out, and a stuffing or dubbing of cod-oil and tallow is rubbed into both sides of the skin, but chiefly the flesh side, by means of a brush, or with the woolly side of a piece of sheep-skin. The skin is now dried in a loft, and as the water only evaporates, the dubbing sinks into the pores. A stove heat is sometimes employed for the purpose, and the neighbourhood is unpleasantly reminded of the fact, by the currier using shavings of leather as fuel. When dry enough for the purpose, the skin is boarded, or worked with a graining board or pommel C (fig. 5), the effect of which is to bring up the grain, or give a granular appearance to the leather, and also to make it supple. The pommel is a piece of hard wood, grooved like a crimping-board, and attached to the hand by means of a strap, whence the word pommel, from the French pommelle, or palm of the hand. The leather passes through various manipulations, each having its distinct name; thus graining consists in folding the skin with the grain sides in contact, and rubbing strongly on the flesh side; brushing, or rubbing the extended skin on the grain side; whitening, or passing a knife with a very fine edge over the skin at the beam, so as to clean the flesh side, preparatory to waxing, which is done just before the skins are sold; for at this point the currier stores his skins, as they can be kept best in the state of finished russet, as it is called previous to waxing. Waxing consists of two parts: the first is the laying on the colour, or blacking of oil, lampblack, and tallow, which is well rubbed in on the flesh side with a hard brush; secondly, the skin is black-sized with stiff size and tallow, laid on with a sponge or a soft brush, and thoroughly rubbed with a glass slicker, a finishing gloss being given with a little thin size. The curried skin is now said to be black on the flesh, or waxed, in which state it is used for the upper leathers of mens' boots and shoes. The leather which is carried on the hair or grain side, is called black on the grain, and is mostly used for the upper leathers of ladies' shoes. In preparing such leather, the waxing is performed as follows:—A solution of sulphate of iron, called copperas-water, or iron-liquor, is applied to the grain side of the wet skin, when the salt, uniting with the gallic acid of the tan, produces an ink dye; stale urine is then applied to the skin, and when dry, the stuffing is applied. The grain is raised, and when dry the skin is whitened, bruised, and again grained; after which a mixture of oil and tallow applied to the grain side, completes the process.

Varnished and Enamelled Leather.—For many years it was found difficult to cause a bright varnish to adhere to leather without cracking; an effect which is now produced by means of boiled linseed oil, mixed with vegetable black and Prussian blue. This composition, of the consistence of a thick paste, is rubbed upon the surface of the leather, and then dried at a temperature of from 150° to 170° Fahr. The process is repeated from three to seven times, and when quite dry, the varnish adheres very firmly, and will bear considerable flexure and tension without cracking. By mixing coloured pigments with the varnish, enamelled leather of various colours may be produced.

Thin Leather.—The process of tanning differs considerably in the mode of treatment with the kind of skin and the result desired. A large number of thin leathers which are intended to be dyed, are tanned in various ways. White leathers are not tanned but tawed, or treated with alum, salt, and some other matters. Wash leather is dressed with oil, or shamoied. But whatever may be the subsequent treatment, the preparatory steps somewhat resemble each other, whereby hair, wool, grease, and other matters, are removed, and the skin is reduced to the state of a gelatinous membrane called pelt. The hair is removed from kid and goat skins, by means of cream of lime; the wool is generally removed by the fell-mongers before the skin is passed to the tanners. Foreign lamb-skins, which are received with the wool on, are washed, scraped on the flesh side, and sweated in a close room, until, in consequence of the putrefactive fermentation, the wool can be easily removed. After this, fatty matters are got rid of by subjecting the skins to hydrostatic pressure; they are next worked at the beam, and pared into shape, treated with lime, and next with dogs' or pigeons' dung if the skins are to be tanned, and with bran and water if they are to be tawed, the object being in either case to get rid of the lime. During these operations the skins are worked a few times at the beam, and are finished by washing in clean water.

Morocco leather is prepared by tanning goat-skins with sumach, and dying on the grain side. Inferior moroccos are prepared from sheep-skins similarly treated, for which purpose each skin of pelt is sewed up into a bag, the grain side outermost, distended with air, and placed in a mordant of tin or alum. They are next placed in a warm coctional bath for red, indigo for blue, orchil for purple, and are worked by hand until the dye has properly struck. For certain colours the tanning precedes the dyeing. The tanning or sumaching is carried on in a large tub, containing a weak solution of sumach in warm water; another and stronger solution is contained in an adjoining vessel, a portion of which, together with some sumach leaves, is poured into the bag; some of the weak solution is then added, the bag is then distended with air, and the skin thrown into the vat. In this way about fifty skins are treated, and are kept in motion a few hours in the sumach tub by means of paddles worked by hand or by machinery. The skins are then taken out and heaped up on a shelf at the side of the tub, the pressure thus produced causing the liquor to escape slowly through the pores of the skin, the bags being shifted about from time to time. The bags are next passed into a second vat containing a stronger solution, where they remain for nine hours. The bags are now opened and washed; fine red skins being finished in a bath of saffron. All the skins are next strained on a sloping board until they are smooth and flat, and in order to improve their appearance in the carrying a little linseed oil may be rubbed on the grain side. They are then hung up in a loft to dry, when they become horny, and are in the crust, as it is called. They next pass through much laborious friction with the pommel, and with a glass-ball; while the peculiar ribbed appearance of morocco is given by means of a ball of boxwood, on which is a number of narrow ridges. Sheep-skin morocco is prepared from split skins; the skin-splitting machine resembles in principle that already described, only as the membrane is thinner certain variations are required. Instead of stretching the skin on a drum, it is passed between two rollers, the lower one of gun metal and solid, and the upper made of gun-metal rings; while between the two rollers, and nearly in contact, is the edge of the sharp knife, which is moved by a crank, as already mentioned. When a skin is introduced between the two rollers, it is dragged through against the knife edge and divided, the solid lower roller supporting the membrane, while the upper one, being capable of moving through a small space by means of its rings, adjusts itself to inequalities in the membrane; where this is thin the rings become depressed, and where it is thick they rise up, so that no part escapes the action of the knife. The divided skins are not sewed up into bags, as from their thinness they can be sumached quickly.

In preparing white leather by tawing, the pelt is made as pure as possible; the best kid leather being prepared from kid skins, while sheep or lamb skins make the inferior kinds. They are first fed with alum and salt in a drum or tumbler made like a huge churn; about 3 lb. of alum, and 4 lb. of salt being used to 120 skins of medium size. The alumina of the alum probably forms some definite compound with the gelatine of the skins, while the salt serves to whiten them. When taken out the skins are washed in water, then allowed to ferment in bran and water, to remove the surplus alum and salt, and to reduce the thickness. They are next dried in a loft, and become tough and brittle, but they are made soft and glossy by means of a dressing of 20 lb. of wheat flour, and the yolks of eight dozen eggs. By rotating the skins in the drums for some time the dressing is absorbed, and scarcely anything but water remains. This dressing is usually repeated, and the skins are hung up to dry. The beautiful softness and elasticity of this leather is now given by manipulation. The skins are first dipped in clean water, worked upon a board, and staked upon a stretching, or softening iron, consisting of a rounded iron plate fixed to the top of an upright beam, by which the skins become extended and made smooth. They are finished by being passed over a hot iron.

When a skin, properly cleaned and soaked in water, has oil or grease forcibly rubbed into its pores, the oily matter combines with the fibres, and renders the skin permanently soft. Water only evaporates during the drying, and the result is a kind of leather called chamois, shammay, or shamoied, from the fact that the skin of the chamois appears to have been the first treated in this manner. When such leather is dyed, it will bear washing, and hence it is also called wash-leather. The best leather of this kind in Great Britain is prepared from doe or sheep skin, while for inferior kinds the flesh side of a split sheep-skin is used, the grain side being tawed for skiver, such as is used for hat-linings, &c. Where the whole skin is employed, the grain is removed by frizing or scraping with pumice-stone or with a round knife. The skins are now placed in bran liquor, wrung out, spread upon a table, sprinkled with a small quantity of oil, rolled up into balls, four skins to the ball, and beaten with wooden hammers in fulling stocks. After two or three hours' beating they are taken out, exposed to the air, again oiled and beaten, which operations are repeated several times. After this the skins are hung up in a warm room, where they undergo a kind of fermentation which promotes the union of the oil with the fibre. They are next scraped with a blunt concave iron, scoured in weak lye to get rid of superfluous oil, washed in water, dried, smoothed, and made supple by means of the stretcher-iron or rollers.

By a variation of the processes of shamowing and tawing, a stout leather, well adapted for driving-bands for machinery, has been produced by Preller's process. The hides and skins being unhairied, &c., are smeared with a paste consisting of starch, oil or fatty substances, salt, and saltpetre, and are then agitated in a drum. After two or three smearings and agitations and drying, the process is complete. In a leather thus formed the fibre of the skin is preserved, and an increased toughness consequently gained.

Recent Improvements in Tanning.—The tanner has not of late years shared in the benefits which the rapid advance of chemistry has conferred on other arts. Mechanical improvements, however, have been introduced, such as the splitting-machine already referred to; the steam-engine is also generally used, and is applied in various ways for grinding bark, for softening foreign hides, and for giving motion to machines for washing, glazing, and finishing leather. The hydrostatic press is also in use for expressing the grease from sheep-skins, the effect of which is to allow the skin to take a more brilliant dye. The abolition of excise duties, improved means of transport, and more liberal commercial relations with other countries, have all tended to the improvement of the leather trade.

Statistics.—The quantities of untanned hides imported into the United Kingdom during the years 1853, 1854, and 1855, were respectively, 231,761, 184,024, and 188,844 cwt. of dry hides; and 518,548, 417,175, and 426,933 cwt. of wet hides; while during the same years there were imported of hides tanned, tawed, curried, or dressed (except Russia hides), 7,286,602, 4,180,315, and 4,368,111 lb. Of leather manufactures, the principal article of import is gloves, which, during the three years above named, amounted to 3,476,341, 3,781,624, and 3,612,639 pairs. The next considerable article of import is boot-fronts, of which, in the year 1855, there were imported 538,604 pairs. Of men's boots and shoes there were only 33,115 pairs; of women's boots and goloshes, 26,975 pairs; of women's shoes of silk, satin, stuff, or leather, 111,054 pairs. During the three years above named, there were exported from the United Kingdom, of untanned hides, dry, 70,295, 94,562, and 123,309 cwt.; of wet hides, 15,521, 17,369, and 38,405 cwt.; while of tanned, tawed, curried, or dressed hides, the quantities were respectively, 29,746, 135,241, 338,422 lb. Of foreign leather manufactures, the only article of export is gloves, of which the number of pairs were respectively, 327,645, 390,987, and 217,458. During the three years above mentioned, the exports of British produce, in leather, were as follows:

| Description | Quantities | Declared Value | |----------------------|------------------|----------------| | Leather, unwrought | 23,740 cwt. | L.195,525 | | Wrought, viz., gloves.| 31,214 lb. | 23,250 | | Of other sorts | 5,404,402 lb. | 1,057,718 | | Saddlery and harness.| | 300,104 |

The gross receipts of customs' duties on leather manufactures imported into the United Kingdom during the years 1853, 1854, and 1855 were respectively, L.58,427, L.61,497, and L.59,984.