CHAPTER VI.

_THE ORIGIN AND CURING OF HIDES AND SKINS._

A considerable proportion of the hides and skins used in leather manufacture are those of animals killed by the butcher for food, and these are frequently employed by the tanner without any preliminary curing. Domestic hides and skins are now generally sold by auction in weekly markets in the principal towns, after sorting and classification in weight and quality.[15] This is in many respects an improvement on the old method of purchase direct from the butcher, but it often leads to delay in delivery, and in hot weather hides suffer from putrefaction. In most cases, the damage is not sufficient seriously to affect the durability of the leather, but the delicate membrane of the “grain” is injured, and the hide or skin unfitted for coloured leather, or any purpose where small damages to appearance are important. Butchers are adverse to the use of salt, because it withdraws water from the hide in the form of brine, and so causes it to lose weight; but much injury would be saved by a light salting, and all hides or skins on which the hair is “slipping” should be regarded as damaged for fine leather manufacture.

[15] The weight of English market-hides as credited to the butcher is usually marked on the edge of the butt near the tail, by cuts with a knife, the mode of numeration being sufficiently explained by Fig. 6, in which cuts crossing the horizontal line each represent 20 lb., that above it 10 lb., while less amounts are expressed in Roman figures.

On the Continent weights are usually given in pounds of half a kilogramme (50 kilos = 110 lb. English). In Paris the marking is on the tail, and is also shown on Fig. 6.

Sheep-skins are not usually bought direct by the tanner, but by the fellmonger, who removes the wool; and as this is usually of much greater value than the skin, the latter is frequently handled very carelessly, and its quality sacrificed for the sake of real or fancied improvement to the wool. In very many cases the skin is “sweated” or “staled” by hanging in a warm and moist chamber, heavily charged with ammonia derived from the putrefaction of the skin, until the wool is sufficiently loosened to be “pulled.” If this treatment is conducted with extreme care the skin may escape serious injury, but in most cases the grain is weakened, and the foundation is laid of damage, which makes itself felt throughout the tanning process. For the purposes of the tanner, a much better way is to lime the skins by painting with thick limewash on the flesh-side, and after folding the skins down the back, flesh-side in, to prevent as much as possible the access of the lime to the wool, to place them in a pit, and cover them with water, till the wool is loosened by the penetration of the lime through the skin. A still more satisfactory method, and one which is in general use in the American stockyards, and to some extent also in Europe, is to wash the skins in water to free them from blood and dirt, and then, laying them in a wet condition, flesh side up, to paint them with a solution containing about 25 per cent. of sulphide of sodium, thickened with lime. The skins, as they are painted, are doubled down the back, flesh-side in, and laid on a floor, overlapping each other like tiles on a roof, for some hours, or overnight, till the wool is sufficiently loosened to pull, after which the pelts are limed and treated in the ordinary way. As a general rule the English fellmonger keeps his skins in lime till they are sold to the tanner, and as in small yards some time is taken to accumulate a parcel, the earlier skins may suffer great injury from overliming. Even sweet fresh limes dissolve the cementing substance of the fibre, and increase the naturally loose texture of the sheep-skin, but the injury is much more considerable when old and stale limes, charged with ammonia and bacterial products, are employed, as is frequently the case. In the American stockyards the skins are generally limed only for the necessary time to act upon the grease, and to swell and differentiate the fibres, and are then at once puered, drenched and preserved by “pickling.” For details of “pickling” see p. 89. It is very probable that the Pullman process of liming (p. 137) would answer well for fellmongered skins, as goods will keep for a considerable length of time uninjured after treatment with calcium chloride.

Where hides or skins cannot be used at once in the fresh state, there is probably no better method of preserving them than the use of salt. Although salt is not fatal to bacteria, it so slows bacterial growth, partly by its direct antiseptic effect on many organisms, and partly by withdrawing water from the skin, that well-salted skins can be kept in good condition for almost an unlimited time. Where it is only required to preserve goods for a week or two, a moderate sprinkling on the flesh side is efficient, but if they are to be preserved for any length of time, more thorough treatment is necessary. It is said that however carefully hides are salted they deteriorate if kept in this condition above twelve months.

The method of salting employed in the Chicago stockyards for “packer” hides may be taken as a good type of a thorough salting. The hides are first trimmed from useless “switches,” and any large portions of adhering fat are removed. The curing takes place in large and cool cellars, with concrete floors. The detail is well given in the following extract from the ‘Shoe and Leather Reporter’:--

“Great care is taken to make the sides of a pack higher than the middle, so that the brine which is made by the juices of the hide coming in contact with the salt will be retained. The brine can only escape by percolation and hence the fibre of the hides is thoroughly cured. The floor of a hide cellar is usually of concrete, and a pack is from 15 to 20 feet long and as wide as the space between the posts which support the floor above. The sides of a pack are built first to a height of from 4 to 6 inches; the cross layers are then put on, generally three on each side, two being inside and one having the butts drawn out to the edge. In a pack 20 feet long, the side layers will contain about 25 medium-sized hides each, and a cross-layer 12 or 14. To begin a pack a truck-load of hides is run along to the front of the place selected, one spreader grasps the butt and his partner the head of a hide, and together they carry it to what is to be the rear of the bed. The hide is then dropped, so that the folded back is parallel to and from 15 to 20 inches from the inside line of the posts, the head a trifle closer than the butt. The front man takes the dewlap and front shank in his left hand, and extends his right along the belly of the hide as far as is necessary to raise the edge, the rear man holding the flank with one hand and the hind shank with the other. They keep their legs well out of the way of the salt thrower, who with a single throw covers the whole hide, being particular that enough salt strikes against the edges held by the men to make a pronounced ridge when they are lapped down. A little salt is thrown on the hair surface and the butt folded over about a foot. The folded edge is then drawn out even with the outer line of the pack. More hides are placed the same way until the corner is high enough. After this, each hide is put further forward to make a level surface from rear to front, the heads at the front corner being folded back as the butts were at the starting place. The other side is built the same way, and then the cross layers are put on alternately until the pack is level, when sides are again built as before. In putting on the first hides of the cross layers, they are thrown over the edge, to lap back again when the salt is thrown on; the layer is then continued on to the front. The spreader who holds the butt does the guiding in every case. He drops the butt down at exactly the proper place, takes the upper flank and shank in each hand, sets one foot on the lower shank to keep it firm, and throws the one in his hands from him with considerable force. The man at the head watches his partner, keeps the folded hide taut, and drops it at the same time as the latter. He takes the fore-shank at the knee in the one hand and the upper head-piece in the other, and setting his foot on the lower side, throws the upper side forward simultaneously with the rear man. Two expert spreaders, accustomed to working together, spread a hide at a single throw, but some little straightening has to be done by hand before the hide is ready for the salt. A gang composed of two spreaders, one salt thrower and a salt trucker put down forty hides an hour. When gangs are doubled, two men do all the spreading; the other two place the hides where they can be got at conveniently. A double gang put down eighty hides an hour. The salt trucker brings the salt to the pack in box-trucks open at one end to permit the entrance of a shovel. The salt thrower keeps the edges and corners of the pack full of salt. He must see that every part of the flesh-side is well covered. Each hide takes two scoop shovelfuls of ground rock or coarse white salt, mixed with an equal quantity of old or second salt. The salt thrower throws the shovel forward and to one side and back again with a peculiar swinging jerk, causing the salt to fall regularly over the entire surface of the hide. The ease and rapidity with which a gang operates depends greatly upon the efficiency of the salt thrower. When the pack gets too high to be comfortable for the men, it is brought to a dead level and covered over with clean salt. It then presents a very neat and workmanlike appearance. Spreaders and salt throwers receive 20 cents an hour, and truckers get 17¹⁄₂ cents. When the temperature is kept at an even average, two weeks is ample time to cure the hides.

“In ‘taking up,’ two men strip the hides from the pack. As they were put down from the rear to the front, they are taken up in the reverse direction. No matter how much loose salt is lying on the top, the man knows exactly where to place his hand on a shank; as the hides are moved forward, the loose salt is thrown off toward the front. One man takes away the salt as it accumulates and trucks it to the salt bins, where it is mixed with new, to be used again. A ‘horse’ made of a network of scantling about 3¹⁄₂ feet wide by 6 feet long, and standing 2¹⁄₂ feet from the floor, is placed in front of the pack, on this the hides, flesh side down, are shaken to remove the salt that is clinging to them. This process requires four men, one at each corner. The hide is brought down heavily on the horse twice, and then spread on the floor flesh side up for examination by the inspectors, of which there are two, one representing the house and the other the buyer of the hides. They sweep off any salt that may be left, and examine for cuts, sores, brands, manure and grubs. They also see that the hide is properly weighed and classified. If the contract calls for a special trim it is now done. Two men then roll the hide, beginning by lapping over the shanks, head and neck. Then the sides are folded over and lapped again, leaving the roll 15 to 18 inches wide. The ends are thrown inward, slightly overlapping each other; a final fold is then given, and the hide is ready to be tied. Rope the size of clothesline is used for tying, and is cut into lengths of about seven feet. It takes three men to tie for a gang such as we have described. After tying, the neat bundles are weighed and loaded on the cars for shipment. A small tare is allowed the buyer. Ordinary workmen in hide cellars get 17¹⁄₂ cents an hour, and inspectors 25 cents an hour.”

About 25 per cent. of salt on the green weight of the hide is required for thorough curing. Rock salt merely crushed is frequently employed, but this is very liable to contain iron in the form of oxide and chloride, which causes the peculiar marbled markings known as “salt-stains.” It is therefore much better to use a white crystallised salt, though it is possible even in this case that stains may arise from the iron present in the blood. Some salt-stains appear also to be due to the action of pigment-bacteria, and not to contain iron. A reddening of the flesh side is often noticed in hides which have been kept in salt long or under unsatisfactory conditions, and is very frequent in wet-salted South American hides. Such hides are said never to produce so firm a leather as those which are sound.

Hides are not unfrequently cured by steeping in salt brine, instead of strewing with dry salt. This method is principally resorted to in order to give fictitious weight. Brined hides do not plump well in tanning, the leather is not so good in quality as from those salted with dry salt, and the cure is much less efficient.

Many hides are not only salted but also dried in order to preserve them. Not much detail has been published with regard to the methods used, which no doubt vary much in different places, but probably in some cases the hides are salted in pile and in others by brining, and then hung up to dry. The principal object of this drying is to economise weight and cost of transport, but it makes the hides much more difficult to wash and soften for tanning, and probably the crystallisation of the salt has a weakening effect on the fibre. Hides cured in this way are styled “dry salted.”

A large number of the hides of the small native cattle of India are imported into this country in a dry-salted condition. The following particulars of their cure are taken from a paper by the Author and Mr. W. Towse.[16]

[16] Journ. Soc. Ch. Ind., 1895, p. 1025.

Dry-salted, or, as they are commonly called “plaster cures,” such as those of Dacca and Mehapore, are thickly coated with a white material, which in the first instance is merely the insoluble portion of a saline earth used in the cure; though in many cases it is applied in larger quantities than necessary, with the simple object of giving weight. The salting is thus described by Mr. W. G. Evans, who some years since had considerable experience as a tanner at Cawnpore:--

“The salt used by the natives is a salt-earth; and is so called by them. It is found extensively in the districts of Cawnpore, Agra, Delhi, Lucknow, Patna, etc., and has no doubt something to do with the localisation of the hide-curing and kindred industries in these places. The mode of procedure used is pretty much as follows:--the salt-earth is mixed into a very thin paste, and this is lightly brushed on to the flesh side one day, and the hide allowed to remain over night under cover. Next day, for best hides, the same solution is again spread on the flesh side of the outstretched hide and rubbed into it with a porous brick, and then for legitimate salting, the hide is allowed to dry under cover. If for export, the saltings may be three or four, and the hides are treated out in the open, subject to the intense heat of the sun; which accounts for the number of hides which go back in the soaks in England and elsewhere.”

“We had a clause in our agreement with hide-factors, that any hides which did not come down to natural suppleness in two days in clean water were to be returned. Of arsenic curing I know nothing, and it is not so much in vogue as formerly. There is quite a trade in Cawnpore, Lucknow, Allahabad, etc., in treating old and inferior hides with new for export, and great efforts are made by native holders to get their stocks down before the rains commence, as they say, and rightly I think, that hides are not worth so much after the rains by 30 per cent. The peculiar latent moisture of the rains affects them very detrimentally.”

Under certain circumstances this mode of cure gives rise to extensive iron-staining of the skins, and analyses of the material scraped off Dacca and Mehapore kips were undertaken with a view to elucidating the causes of this injury. The following are the results of the analyses referred to, which were made upon the residue after the rather considerable quantity of fibrous organic matter, which had been scraped off with the cure, had been destroyed by ignition, together no doubt with traces of ammoniacal salts:--

------+---------------+------------+------------+------ | ---- | Dacca. | Mehapore. | | |Entire Cure.|Entire Cure.| |---------------+------------+------------+------ | | | | |Sand and silica| 20·55 | 27·38 | |Fe₂O₃ | 2·77 | 1·86 | |Al₂O₃ | 2·48 | 2·74 | |Mn₃O₄ | 0·60 | 0·40 | |CaO | 2·60 | 3·70 | |MgO | 3·38 | 3·69 | |Na₂O | 28·97 | 26·80 | |SO₃ | 38·90 | 33·75 | |Cl | 0·22 | 0·18 | |H₃PO₄ and CO₂ | Traces | Traces | | +------------+------------+ | | 100·47 | 100·50 | ------+---------------+------------+------------+------

The soluble salts of the Dacca cure were also analysed separately with the following result:--

CaO 0·70 MgO 0·60 Na₂O 29·00 SO₃ 37·90 Cl ·22 Insoluble 32·12 ------ 100·54

It thus consisted exclusively of sulphates, with the exception of a trace of chloride. The cures, after ignition, were both neutral to phenolphthalein, but before ignition the Dacca was distinctly alkaline, in consequence probably of the presence of ammonium salts, and both showed considerably larger traces of carbonates before than after.

The most striking feature of these analyses is the absence of more than the smallest traces of chlorides. The cures are thus practically free from common salt, and owe their antiseptic power to the sodium sulphate which they contain, and which indeed forms their principal constituent. Nitrates appear to be entirely absent. Sodium sulphate sometimes forms large crystals in pits used for soaking these kips.

The iron-staining of hides which has been mentioned appears to result only when the hides after cure are exposed for a lengthened period to a moist atmosphere, in which the carbonic acid present probably also plays its part, the iron passing into solution as hydric carbonate.

The analyses show a striking resemblance to those of the soda deposits of Wyoming, given by Dr. Attfield,[17] except that their percentage of sodium carbonate is smaller, which is quite intelligible in the light of Mr. Brunner’s abstract on the ‘Probable origin of natural deposits of sodium carbonate,’[18] which supports the view that the sodium carbonate is derived from sodium sulphate by the reducing and carbonating action of low organisms.

[17] Journ. Soc. Ch. Ind., 1895, p. 4.

[18] Ibid., 1893, p. 116.

It may be noted here that the preservative properties of sodium sulphate are well known, and the anhydrous sulphate has been recommended as a substitute for common salt (see p. 23).

Drying is a very common method of preserving hides as well as other putrescible matters. It has no effect in killing bacteria, but putrefaction can only go on in presence of a considerable amount of moisture. As applied to hides, it is, to the tanner, one of the least satisfactory modes of cure, involving very considerable difficulties in bringing hides back to the moist and swollen condition which is necessary at the outset of his operations, but it is the only practical method in districts far from the coast and with primitive modes of transit, both on account of the cost of salt, and the lessened weight of the dried hide. Great differences are found in the ease with which dried hides soften, according to the way in which the drying has been accomplished, the difficulty being greater the higher the temperature which has been used (see p. 111). The best mode of drying is to hang in the shade in a good draught of cool air, with the flesh side out. Hides or skins dried in a tropical sun are not only difficult to soften, but are liable to damaged portions, which either refuse to soften, or blister and go to pieces in liming, owing to the structure of the hide being destroyed by heat, the outer surface drying first and forming an impervious layer which hinders evaporation from the inside, so that the moist interior becomes melted, while the outside appears quite sound. Such injuries are often only to be discovered by soaking and liming. Very similar damage may occur from putrefaction of the interior after the outside has become dry, and to get good results, the drying must be gradual, but rapid, especially in hot climates. South American hides are mostly dried in the sun, suspended by head and tail from stakes, with the hair side out.

The risk of injury by putrefaction during drying is diminished by the use of antiseptics. Solutions of arsenic have been frequently used for this purpose, and many of the dried Indian kips are of what are known as “arsenic cures,” although the writer has never been able to detect arsenic in any which he has examined, and its use seems by no means general. The arsenious acid is usually dissolved in soda solutions. Unless used pretty freely it has little antiseptic effect, but is useful in preventing the attacks of insects, which are often very destructive. The larva of a small beetle, _Dermestes vulpinus_, frequently devours the whole tissue of patches of the hide, leaving only the epidermis.

It may be well here to say a few words about the injuries and defects to which hides and skins are liable, although some of them are not strictly due to the cure. The most serious, and yet preventable injury is that due to butchers’ cuts. As the value of the hide bears only a small proportion to that of the meat, many butchers do their work extremely carelessly, and this is encouraged by the loose classification of “damaged hides” in some markets. There is also an idea that the appearance of the meat is improved by a thin layer of the white skin-tissue being left on it, and for this reason as well as mere carelessness, butchers frequently score the flanks of the hide with shallow cuts which greatly diminish its value. The “packer hides” of the United States, and the products of the large saladeros or slaughtering (“salting”) establishments of South America, such as Liebig’s, show what can be done by skilled work in this respect. In the United States, much of the flaying is done by means of a wooden cleaver, instead of a sharp knife. Another method to some extent in use, and which may be recommended for calf and sheep skins, is to inflate the carcase before skinning, with air from a compressing syringe, which tears the connecting tissue between the skin and the body, and renders flaying much easier.

Brands are a great source of damage to hides, but where cattle roam at large on unfenced plains, as on the prairies of Texas and the Pampas of South America, it seems indispensable for the recognition of ownership; no other mode of marking being sufficiently permanent and conspicuous. It is unfortunate, that as the animals crowd together, and cannot be closely approached, it is necessary that the brands should not only be large, but placed on the most valuable part of the hide. Generally on the Pampas an effort is made to keep them on one side only, so that in South American hides it is possible to select clear and branded sides. In the United States much land is now fenced with barbed wire, which while it obviates the necessity of branding, introduces another evil in the form of “barbed wire scratches,” which are frequently troublesome in “packer hides.”

In countries where cattle are used for draught purposes, goadmarks are a frequent source of injury, and some of the large cattle-ticks do considerable damage to the hides of Spain and South America. From the tanners’ point of view, however, the most injurious insects are the “bot-flies” or “warble-flies” (_Hypoderma bovis_ and allied species, Fig. 7). There is still some controversy as to how the eggs of these insects are deposited. In the horse-bot fly it is known that the eggs, first deposited on the skin, are licked off and swallowed by the animal, and develop in the stomach, where they pass their larval and pupal life hanging on to its interior coats, and only drop off and are passed out with the dung before their final change to the complete fly. Fortified by this, and by some direct observation, some American naturalists are of opinion that the American species at least, hatches in the stomach, and as a minute larva wanders through all the intervening tissues till it reaches the skin, where it undergoes its further development. The late Miss Ormerod, who has made a careful study of the English species,[19] states that the egg hatches on the hair, and that the _larva_ simply eats its way below the skin, leaving a minute red puncture which it subsequently enlarges to obtain air for its spiracles, which are in the tail. As it grows it continues to irritate the lower part of the cavity with hooked mandibles, and lives on the pus and matter so produced. It grows to a length of fully ³⁄₄ inch, and the cavity, Fig. 8, situated between the skin and the subcutaneous tissue is often as large as half a walnut. It remains in the sac not only during its larval, but its pupal stage, which do not differ much in appearance, and falls out on the ground before complete development. In small numbers, the warble seems to do little injury to the general health of the animal, but cases have been known where animals have actually died of the inflammation produced. Some idea of the extent of the plague may be realised from the statement that an Indian kip in the possession of the writer has not less than 680 warble holes, and that almost equal numbers have been counted in English hides. Preventive measures are the sheltering of the cattle during the summer months when the fly is most prevalent; the application of mixtures of oil or grease with tar-oil and sulphur to the hair, to prevent egg-laying; and the destruction of the _larva_ in its early stages, in autumn and winter by smearing the breathing aperture with grease, or better, with mercurial ointment. When this is done sufficiently early, the hole heals up without permanent injury, but when it is allowed to remain open during the period of growth, its sides become partially coated by the growth of epidermis, and this permanently prevents their proper union by skin-tissue. It is believed that if the _larvæ_ were systematically destroyed in a district, they would soon become extinct, as they are not supposed to travel far.

[19] ‘Some Observations on the Œstridæ,’ E. A. Ormerod, Simpkin and Marshall, London, 1884, price 4_d._

A very troublesome injury to the skins of lambs and sheep is the disease known as “cockle,” in which the skin becomes thickly dotted with spots of thickened tissue, which bear some fanciful resemblance in form to a cockleshell. The affection is prevalent during the spring while the wool is thick, and disappears almost immediately on shearing, but little is known of its causes or mode of prevention.

Climate and breed have a considerable effect on the quality of hides and skins. As a rule the less highly bred races, and those which are most exposed to the extremes of weather, have the thickest hides, and in most cases highly bred animals have had their meat-producing, or in the case of sheep, their wool-bearing qualities developed at the expense of the characteristics most valued by the tanner.