Transcriber's note:
Minor spelling and punctuation inconsistencies been harmonized. Obvious printer errors have been repaired. The letters A and B have been added on the illustration Fig. 11 (page [59]).

LEATHER

Common Commodities and
Industries Series

Each book in crown 8vo, cloth, with many
illustrations, charts, etc. 2s. 6d. net.

Tea: From Grower to Consumer. By A. Ibbetson.

Coffee: From Grower to Consumer. By B. B. Keable.

Sugar: Cane and Beet. By Geo. Martineau, C.B.

Cotton: From the Raw Material to the Finished Product. By R. J. Peake.

Rubber: Production and Utilisation of the Raw Product. By C. Beadle and H. P. Stevens, M.A., Ph.D., F.I.C.

Iron and Steel: Their Production and Manufacture. By C. Hood.

Silk: Its Production and Manufacture. By Luther Hooper.

Tobacco: From Grower to Smoker. By A. E. Tanner.

Wool: From the Raw Material to the Finished Product. By J. A. Hunter.

Coal: Its Origin, Method of Working, and Preparation for the Market. By Francis H. Wilson, M.Inst.M.E.

Linen: From the Field to the Finished Product. By Alfred S. Moore.

Timber: From the Forest to its Use in Commerce. By William Bullock.

Clays and Clay Products. By A. B. Searle.

Leather: From the Raw Material to the Finished Product. By K. J. Adcock.

Oils: Animal, Vegetable, Essential, and Mineral. By C. Ainsworth Mitchell, B.A., F.I.C.

Wheat and its Products. By A. Millar.

Copper: From the Ore to the Metal. By H. K. Picard, Assoc. Royal School of Mines, Mem. Inst. of Min. and Met.

Paper: Its History, Sources, and Production. By H. A. Maddox.

Glass and Glass Manufacture. By Percival Marson.

Soap: Its Composition, Manufacture, and Properties. By William H. Simmons.

The Motor Industry. By Horace Wyatt, B.A.

The Boot and Shoe Industry. By J. S. Harding.

Gums and Resins. By Ernest J. Parry.

Furniture. By H. E. Binstead.

Other Volumes in preparation.

BLEACHING OIL-TANNED LEATHER BY EXPOSURE TO THE SUN
The Rosary Leather Mills. Ashtead

PITMAN'S COMMON COMMODITIES
AND INDUSTRIES

LEATHER
FROM THE RAW MATERIAL TO THE
FINISHED PRODUCT

BY
K. J. ADCOCK

London
Sir Isaac Pitman & Sons, Ltd., 1 Amen Corner, E.C.4
Bath, Melbourne and New York

Printed by Sir Isaac Pitman
& Sons, Ltd., London, Bath,
Melbourne and New York

CONTENTS

LIST OF ILLUSTRATIONS

LEATHER

CHAPTER I
EVOLUTION OF THE ART OF LEATHER MANUFACTURE

Before describing the making of leather by up-to-date methods, it may be useful to attempt to outline the evolution of the ancient art of tanning and dyeing skins. As everyone knows, leather is the preserved skin of various animals, but the origin of the conversion of raw skins into an imputrescible material will probably never be traced, and it can only be assumed that the processes necessary to produce leather from skins were gradually and, in most cases, accidentally discovered. Long before the Christian era, the ancient Egyptians had succeeded in bringing the manufacture of leather to remarkable perfection, and, had they at their service the wonderful machinery now available to the leather industry, it is certain that their productions would have lost little or nothing by comparison with modern leather. Happily, specimens of ancient Egyptian leather have been preserved in one national museum, and, although they are said to have been made at least 3,000 years ago, the colour and natural strength of the leather are unimpaired.

Judging by the advanced state of the art of leather manufacture in the early Egyptian period, it is obvious that the origin of its manufacture must have considerably antedated that period, and, indeed, it would be necessary to go back almost to the creation of man to find the origin of the use of preserved animal skins for clothing. The primitive method would naturally consist of simply drying the skin, in which condition it would keep for many years unless it came into contact with moisture, though its horniness would no doubt cause the wearer much discomfort. It must not be supposed that the wearing of dried raw skins with the hair left on was impracticable, for even to-day some of the skins of fur-bearing animals used for personal adornment are cured in this primitive way, with the additional treatment with napthalene for disinfecting purposes and keeping away injurious insects and moths, the object of the limited amount of dressing being to preserve the natural strength and coloration of the fur. In such a condition, however, the skins are liable to acquire an unpleasant odour, and for hygienic reasons it is advisable that all skins in the hair used for clothing or rugs should be properly dressed, so that no decay sets in to loosen the hair or fur.

Even now, the process of simply drying hides and skins to preserve them before sending them to the tanner is largely practised, especially in hot climates and in those countries where salt is not readily available. This process of curing rests on the chemical theory of dehydration, which, in a modified form, has recently been successfully applied to some experiments in making leather.

Finding that the simple drying of skins would not properly prepare them for clothing, primeval man would naturally look for some means of treating them to conserve their original softness and pliability, and the nearest substances at hand would be animal fats and brains. It is almost safe to assume that this process was the first by which hides were preserved in a state differing from their original condition, the oxidation of the fatty matters naturally producing a partial tannage. The effect of smoke may also have been discovered in the earliest days of skin-curing, and it is reported that even now one or two tribes use smoke to preserve skins.

The somewhat imperfect preservation of the hides by this method would lead to further experiments being made, which evidently resulted in the discovery of the tanning effect of leaves, twigs, and barks of trees when soaked in water. It may be that the preservative effect of alum was discovered even before the vegetable tanning process, for the original Japanese white leather was made simply by steeping the raw hides in certain rivers which contained a bed-rock of alum. This primitive process is even followed to-day in one or two places in Japan, but the leather is afterwards treated with oil to impart tensile strength and increased suppleness. Strictly speaking, these hides are not leather when finished, and they are quite unsuitable for boots; but, being the toughest material known in the leather trade, with the possible exception of raw hide, it is particularly suitable and chiefly used for brace ends, and occasionally for ladies' belts. It must not be inferred from reference to this process that the Japanese only use this earliest method of making leather; on the contrary, they are producing all classes of leather, and especially belting and sole, by modern European methods, and it may not be long before their competition with American and European productions becomes an accomplished fact.

The available information seems to show that, until about thirty years ago, the development of the industry was mainly the result of accidental discoveries, and that the theory of tanning and leather-dressing was imperfectly understood until within quite recent times. Records of the leather trade 300 years ago prove that the methods then in vogue were of the rudest kind; further, they show that the practice of skimping the tanning process was not unknown in those days, for a contemporaneous author describes the horny condition of some of the leather which, despite the Government inspection, appeared to have passed into the old Leadenhall market for sale by the simple operation of "greasing the fist of the seller." Spain and Hungary had by that time established the manufacture of morocco and curried leather on a fairly sound basis, while a few years later France began to develop the industry of leather manufacture. Until about twenty years ago, waxed calf, crup, calf kid, and alum-tanned kid were staple upper leathers, together with the old Spanish cordovan leather. The sole leather used in England was chiefly the output of tanneries in the United Kingdom. About twenty years ago, however, the successful application of the chrome tanning process caused quite a revolution in the leather trade, with the result that about nine-tenths of the world's production of boot upper leather is chrome-tanned. The introduction of this process on a practical scale gave a great impetus to the work of chemists, who have since made some remarkable discoveries and have placed the art of leather manufacture on a scientific basis.

The old methods, however, are by no means obsolete, and it is somewhat remarkable to find that a British patent was taken out last year (1914) for converting hides and skins into leather by treating them with brains and smoke.

CHAPTER II
HIDES AND SKINS

The hides and skins of animals form the principal raw material of the tanner. Technically, the term "hides" is applied to the skins of the larger animals, while the word "skins" is used in the case of the smaller animals. Thus, the tanner speaks of ox, cow, bull and horse hides, and of calf, sheep, and goat skins. There is an intermediate size between a full-grown calf skin and a small hide, and this is known as a "kip," but the line of demarcation is not very clear.

Buyers often settle the difficulty by examining the growth marks and the irregular substance of the skin, and, if these are marked features, it is classified as a kip. The condition of the hides of cattle is usually inferior during the six months after the animal has become a yearling. East India tanned hides, which are largely imported into England, are frequently described as E.I. "kips" in the trade. This is hardly accurate, but the mistake is probably due to the small size of full-grown Indian hides, which are very little larger than the average European kips. It is interesting to observe that furriers always refer to both their raw material and the finished product as skins, irrespective of the size of the fur-bearing animals. Most of the skins of wild animals are dressed without removing the hair or fur, and this is quite a distinct trade from leather manufacture, the only exception being the dressing of closely cut and fine-haired calf skins for slippers and fancy articles.

Practically every country in the world contributes to the supply of hides and skins, but there are a few countries which are far in advance of the others in the industries of cattle and sheep-raising. The sources of tanners' raw material have undergone great changes since the establishment of freezing and chilling stores for the preparation of meat for export, and the market prices of hides are to a large extent controlled by the supply in North and South America, South Africa, and Australia. Whether or not the concentration of these huge meat works into two or three centres is likely to benefit the leather trade is a debatable point. The flaying, trimming, and curing of hides in these establishments are certainly superior to the work done by the average butcher, while, owing to the large numbers of cattle slaughtered, the hides can be closely selected. On the other hand, the value of hides and skins has risen enormously in the last decade, the period coincident with the rapid growth of the chilled and frozen meat industry, but the increased use of leather in many directions may be mainly responsible for the higher cost of the raw material, although it is obvious that the concentration of the chief supplies of hides in a few lands must tend to increase the severity of the competition among buyers. Apart from the high prices of the hides, the concentration of the meat industry in large chilling and freezing works has had the effect of increasing the prices of beef and mutton, which are now higher in price than freshly-killed English meat was a few years ago. It appears to have been a grave error on the part of the British Government when they stopped the imports of live cattle owing to the fear of foot-and-mouth disease being communicated to domestic herds. The disease has broken out in several places since the embargo was imposed, so that the theory that the infection was only carried by imported live cattle has been clearly disproved. The butchering of cattle provides a large amount of work in subsidiary industries, and the Government embargo on the importation of live cattle has caused a great deal of distress in Deptford and Birkenhead, where large abattoirs were erected for the reception of live cattle, which used to be imported in fairly large numbers. There is no danger of foot-and-mouth disease getting beyond the abattoirs or of the slaughter of diseased cattle for food, and both tanners and butchers hope to see the removal of the embargo. So far as possible, each country should raise its own cattle to provide its own meat supply, and this principle is recognised by many countries which prohibit the import of foreign meat: but, owing to the rapid growth of populations in industrial countries, with the consequent increase in the value of land, it has become impracticable to raise enough cattle to supply domestic needs. Even the United States of America, which formerly had a great cattle-raising industry, has lately been obliged to import live cattle to meet the requirements of its inhabitants. Similar conditions prevail almost throughout Europe, and tanners have to look to South America, Australia, and Africa for large supplies of raw hides, although there are still some tanners in the United Kingdom who use only the hides produced in this country.

The bulk of the production of hides and skins in the United Kingdom is disposed of at weekly public auctions in the principal towns: London, Manchester, Liverpool, Leeds, Birmingham, Newcastle, and Glasgow being the largest centres of distribution. However, there is still a large quantity bought by private treaty, and opinions are divided as to which is the better method of buying. Before the establishment of public auctions, hides were very cheap, but tanners were unable to get a good selection, although, for sole leather, that was not a very important matter. Public auctions have become so firmly established that it would be impossible for tanners to revert to the old system even if they desired it. The competition of private buyers with the auction markets has certainly benefited the butcher at the expense of the tanner, and the weighing and classification of hides ultimately became so irregular in many markets that the Tanners' Federation of the United Kingdom had to take strong action not long ago to protect their interests. They demanded the appointment of an independent inspector at each market to check the weighing and sorting of the hides, but this was successfully resisted by the market proprietors, who eventually agreed to the tanners appointing travelling inspectors to visit the markets periodically. The system is said to have improved matters.

The English markets do not collect enough hides to permit their close sorting, so that, while the hides are graded according to weight and quality and the sex of the animal, the question of varying substances is generally ignored. There is usually a difference of 10 lb. in each class where the hides are sorted by weight Ox, cow, heifer, and bull hides are sold separately, as each sort has a different value. Bull hides are comparatively poor in quality, owing to their irregular substance and strong growth marks in the neck. Ox hides are the most suitable for sole leather and belting, while cows' and heifers' are used mainly for dressing hides, which are finished into bag, case, strap, and boot leathers. The hides known as Scotch and Hereford runts are the best of those produced in the United Kingdom, as they are well-grown, compact, and well-suited to the making of sole leather and belting. The grading of the weight of these hides at the auction markets is generally as follows: 100 lb. and above, 90-99 lb., 80-89 lb., 70-79 lb., 60-69 lb., 59 lb. and less. This does not give an ideal classification, as hides vary so much in texture and substance, and it is quite possible to find spready hides of poor substance and quality which would be heavier than a small but compact and well-grown hide. It would be better from the tanner's point of view if the hides were selected according to substance and quality. There are not many bull hides grown in the United Kingdom, and in many markets they are not classed by weight but simply into best and secondary qualities. Horse hides are of even less value than those of bulls, owing to their weaker texture and irregular substance. That part of the skin under the mane is almost worthless, while the flanks and sides are only useful for a secondary class of boot upper leather, although some fairly good patent sides have lately been produced from horse hide, which is suitable for that purpose owing to its soft grain and pliable texture when tanned. The most valuable part of a horse hide is the butt, which consists of the part known as the "shell." This shell is covered with an extremely fine grain which is not found in any other part of the hide. The well-known crup leather is made from the shell of the horse hide.

In addition to hides, there are fairly large quantities of calf and sheep skins sold at the weekly auctions, but veal is not such an important article of food in England as it is on the Continent. Sheep skins are far more numerous, as Great Britain is a big mutton-consuming country. Home supplies of both hides and skins have been greatly reduced, however, by the immense import of frozen and chilled meat.

Although the domestic supply of hides and skins is quite inadequate to meet the needs of British tanners, a large proportion is exported. American tanners buy large quantities of the best hides and pickled sheep skins. The latter are dewoolled and preserved by a process of pickling with formic or sulphuric acid and salt before exportation. Those preliminary operations are the work of the fellmonger. Nearly all of the horse hides produced in the United Kingdom are, or were before the War, sent to Germany, and British leather-dressers appear to have lost the art of finishing horse hide, or are unable to convert it into leather profitably.

The interchange of raw hides between various countries, and even between those where leather manufacture is an important industry, is somewhat remarkable, and only goes to prove that the concentration of a particular industry in one or two centres of the world gives these places a great advantage in regard to labour, organisation, and technical skill, even over those countries where the raw material is plentiful. Theoretically and economically it should be advantageous to establish tanneries close to the supply of raw hides, since the latter, under present conditions of preservation, steadily deteriorate from the time they are removed from the carcase until they reach the tannery. In some countries the methods of preserving hides are actually so bad that the hides have often lost half of their value before the tanner gets them. Two or three of the largest American meat-packing establishments have erected or taken over tanneries to deal with raw hides, one of their by-products. Tanneries have also been erected near some of the large meat works in the Argentine, but the development of the leather trade there is by no means rapid, and at present the United States of America is the largest leather-producing country in the world. Germany, France, and the United Kingdom come next in the order named.

South Africa is an important source of supply of raw material, and large quantities of Cape hides are sent to England. The production of raw hides there is likely to be on a very large scale in a few years' time, as the raising of Afrikander and other breeds of cattle is sure to become an important industry now that the ravages of the terrible disease, known as "tick," have been checked. China is another large hide-exporting country; most of the hides from this source are dried in the open air and are generally arsenicated to prevent the ravages of insects. Immense quantities are also provided in all other populous countries, but the demand for leather is generally greater than the production of raw material in those countries. India is a noteworthy exception to this general rule; the production of Indian hides is enormous, and, although the leather trade is being developed, there is a large surplus of raw hides and skins for export. Large quantities are roughly tanned, however, and exported to England, Germany, France, and other European countries to be dressed and finished. The greater proportion of these hides and skins is used for the making of shoe leather, while a good quantity is used for bag (hide) and imitation morocco (goat) leathers.

Naturally, there is in the aggregate a considerable supply of raw hides and skins from other parts of the world in addition to that from the countries specially named, and new sources are being frequently found.

It would be impossible to describe the characteristics of the numerous varieties of hides and skins except in a full-sized text-book, but a brief description of the principal sorts may be given.

Some of the varieties produced in the United Kingdom have already been described. In the main, there is not a great deal of difference in the hides of various breeds, but there is a type of well-grown and stout hides specially suitable for sole and belting leather; this class is known as runts, and these hides are obtained from the Scotch and Hereford breeds of cattle. The Scotch runts from the Highland cattle are more valuable than any other class of hide found in the United Kingdom; unfortunately, the production is small. Irish cattle also yield good hides, but in England the interests of the cattle owner, or feeder, are in conflict with those of the tanner, for the system of artificially fattening cattle with oil cakes tends to make the hides very greasy and weaker in the fibres than those hides from animals which are reared on natural food-stuffs.

This grease is very difficult to remove and reduces the selling value of sole leather by about 2d. per lb. The use of a borax solution for soaking partially removes the grease, while it has been proposed that the pelts should be treated with a solution of hyposulphite of soda just before placing them in the tan liquors. A drawback of the latter process is that a little weight is lost in the finished leather.

The trouble caused by the presence of a large quantity of natural grease is even more pronounced in sheep skins than in cattle hides. Naturally, a sheep arrives at maturity in about two years; but by the modern system of intensive feeding with oily food-stuffs it can be fattened in about ten months. This is obviously a great advantage to the sheep-breeder; in other respects it is an unsatisfactory method, for the mutton is not so well matured, and, therefore, is not so nourishing; it contains too large a proportion of fat, and the skins are very greasy and weak in fibre. The excess of grease does not detract from the value of the wool, and may even be beneficial.

There are several varieties of sheep in the United Kingdom, with widely different characteristics. A fellmonger should have a good knowledge of the skins of various breeds in order to buy the particular sorts that will meet the requirements of his customers, as his business is to separate the wool from the skins and to supply the former to the woollen factories and the latter to the leather-dressers. He has, therefore, to study carefully both the wool and pelt markets. While some breeds of sheep yield fine long wool of bright lustre, others have comparatively short-stapled, and "kempy" wool. Between these two classes, there are numerous grades, and the task of sorting the various qualities of wool in those fellmongeries where several classes of skins are worked is by no means easy. It is a generally accepted axiom that the pelt (i.e., the skin denuded of wool) is weaker in fibre in those skins which yield the finest and best wool. In support of this, the Welsh mountain sheep may be cited. This sheep has short, curly wool, but its skin is tough and strong on the grain. In fact, it is about the only breed suitable for roller leather, which is used in the cotton industry for covering the drawing rollers of spinning-machines. Most of this leather is made in North Wales, whence it is exported to every country where the cotton industry is carried on.

Notable exceptions of the general rule regarding the relative qualities of wool and pelts are found in two or three English varieties, namely: the Lincolns, Leicesters and black-faced Suffolks, which produce both fine wool and large pelts of good quality.

Other useful British breeds are the Southdowns, Devons, Shropshires, Wensleydales, Scotch black-faced, Cotswolds, and Kerrys. Of the imported varieties, the New Zealand and Cape sheep skins are the best. The former, principally merino stock, not only provide very fine wool, but also pelts of choice quality and large pattern. Although the quality of the wool of Australian merino sheep is little, if any, inferior to that of the New Zealand type, the skins are not so good in quality, due, no doubt, to the hotter climate, which is favourable to the breeding of insects and other pests which damage the skins. The Cape sheep provide a skin which is quite different in texture from that of any other breed. It has a certain looseness of texture and softness of grain which make it particularly suitable for the manufacture of glove leather.

South America is another large sheep-breeding country; but the skins of this variety are not largely imported into England, most of them being sent to Mazamet, the great centre of the fellmongering industry in France. Buenos Aires skins are the most favoured of the South American skins, owing to their large size and good substance. Monte Videos are also very fine skins.

Smyrnas and Bagdads are other well-known varieties, but they are generally imported in a rough-tanned condition, or, as it is known technically, "in the crust." Leather-dressers finish them for various purposes, but mainly for boot and shoe lining leather. When properly tanned by the natives, these skins produce a supple finish, especially those of the Smyrna variety. Unfortunately, many lots are merely coloured on the surface with the tan liquor, with the result that they dry hard and tinny; such partially-tanned leather is very difficult to finish and is rarely satisfactory. Even when the tannage is completed elsewhere before finishing them, they never produce such good leather as skins properly tanned in the first instance.

Russia is another important country for the production of all kinds of raw hides and skins suitable for leather manufacture. American tanners buy very largely from this market, and a few enterprising firms even send their own representatives to the great annual fair held at Nishni Novgorod, where large quantities of dried hides and skins, besides many other kinds of produce, are offered for sale. British tanners take comparatively little interest in this important supply, but, as a result of the great European War, an increase of trade between Russia and the United Kingdom is anticipated, although the Russian leather trade is developing rapidly and will absorb increasing quantities of native raw material.

Excepting a few in Ireland, raw goat skins are not produced in Great Britain. The chief drawback to goat breeding there is a somewhat inexplicable aversion on the part of the public to the flesh of goats; although another reason may be the destructive nature of the animals themselves, for they devour and uproot anything edible that comes in their way. It is, perhaps, unfortunate that some of the large areas of uncultivated land in Great Britain are not given up to the breeding of goats on a large scale, since these hardy animals will thrive on rough, hilly lands. Apart from the value of the meat, it might be a paying proposition to rear large herds of goats for the supply of milk (which is more nourishing than cows') and skins. Leather-dressers are, therefore, dependent on imported supplies, of which the principal sources are India (North-Western District), Mexico, Arabia, Africa, South America, and several European countries.

Goat skins from the main sources of supply vary very much in quality—even those produced in the same country. In India, for example, skins may be obtained in some districts which can be made into leather to sell at about 5d. per square foot; from another district, when finished into the same kind of leather, say glazed kid, they may be worth 1s. 4d.[1] per foot. Fineness and clearness of grain and good substance are the main essentials of a first-class goat-skin leather; unfortunately these qualities are rarely combined in one class of skin, and there is a decided surplus of light thin skins which are hardly saleable, even for ladies' shoes. Some American shoemakers overcome this difficulty by pasting a piece of cloth on the back of the skin. In fairness to the buyer, the boots made of such leather should be specially marked, as the wearing quality of a backed thin leather is not to be compared with one naturally stout.

[1] It must be understood that, owing to the war, these prices have been greatly increased.

The skins of goats are used for many purposes besides the manufacture of the famous glacé kid leather; gloves, moroccos for bookbinding, upholstery for furniture, fancy articles such as purses, pocket-books, bags, and ladies' belts all require large quantities of goat and kid skins. It may be pointed out here, however, that quite nine-tenths of the so-called kid gloves are made of lamb and sheep skins. In appearance, there is very little difference between the real kid and the lamb skin gloves, but the former are more durable and warmer in wear than the latter.

With an enormous range of qualities, it is a difficult task for the goat-skin dresser to find the most suitable sorts for his trade. The skins used in the glove industry are largely obtained from the Near Eastern countries, Arabia, Austria, Spain, and the Cape. The selections best suited to the making of glazed and "patent" (japanned) kid are found in the North-Western provinces of India, Brazil, China, Russia (especially the Asiatic provinces), Mexico, the Cape, and Arabia. The Indian goats known as the Patnas, which are collected in the district of Behar, are commonly supposed to be the best in the world, chiefly because of their fine grain and stout substance; but the best Brazilian and Mexican skins are equally good in quality. The best moroccos for fancy articles are made from Continental skins, and in this respect Germany has the great advantage of a good supply of native skins. Norway and Spain also provide skins suitable for real morocco leather. A very large quantity of Indian-tanned goat skins are imported into European countries and dressed for "morocco" leather. There should be a distinctive name for this class of leather, as, although it is similar in appearance, it is not nearly so good in quality as the real morocco.

In addition to cattle hides, sheep, and goat skins, which are the main supply of raw material for leather, other kinds of hides and skins are utilised. Horse hides, which, in the United Kingdom, are graded according to size and quality in four or five selections and sold by the piece, are largely used on the Continent, and especially in Germany; nearly all of the British production being sold to that country. When chrome tanned, these hides produce quite a serviceable upper leather of good wearing quality, but, owing to their somewhat loose texture, the characteristic grain of box calf cannot be reproduced naturally, and the surface of the leather has, therefore, to be printed. This style of finished leather does not meet with the favour of British boot manufacturers, and the industry has not been greatly developed in consequence. In view of the increasing cost of other kinds of leather, however, more attention may be paid to that made from horse hide, but the supply of this raw material is very small compared to the production on the Continent, where horse flesh is consumed freely. Russia produces large quantities of horse hides and colt skins, most of which are exported to the United States of America, where they are made chiefly into japanned, or so-called "patent," leather, which commands a very high price in relation to the cost of the raw material.

Next in importance to horse hides is the pig skin, which produces a wonderfully tough leather. The pig skin leather industry is chiefly confined to Scotland and Germany, the reason being that the skins are left on the carcases in the other parts of the world. On the average, a pig skin is worth about 6s., yet it is seldom removed from the carcase. One reason is the great difficulty of flaying the animal; it appears to be almost impossible by present methods to remove the skin without cutting away a large quantity of fat, and the value of the skin compared to the loss of weight of the meat offers very little inducement to remove the skin, in addition to which, the custom of leaving the rind on bacon and pork effectually prevents any attempt at present to increase the supply of pig skins. This is a great loss to the leather trade, for the pig skin is particularly suitable for saddles and various kinds of strong leather goods. Imitation pig-skin leather is made from hides, shoulders, bellies, or persians, but real pig skin is distinguished from the imitation by its peculiarly marked grain, formed of groups of three small holes which penetrate well into the skin and form part of the sheaths of the pig's bristles.

Among other skins useful for leather are those of the wallaby, kangaroo, dog, lizard, crocodile, alligator, ichneumon, frog (Japanese), deer, antelope, and chamois, while it is said that even rabbit skins have been pressed into service in Germany, though they cannot have much value owing to their small size and thin substance. Dog-skin leather wears well, mainly on account of the large amount of natural grease present in the skin, but the supplies are naturally small. The hides of the walrus, elephant, rhinoceros, hippopotamus, and other wild animals are also tanned in small quantities, walrus leather being well adapted for knife and sword polishing.

The mammals also contribute their quota to the supply of raw material of the leather trade, the seal perhaps, being the most important. This refers to the hairy seal hunted off the North American coast.

The raw skins are shipped chiefly from Newfoundland, where the industry of seal fishing is well organised and provides employment for about 6,000 men. The seal caught in the North Atlantic Ocean is hairy and quite distinct from the fur seal captured in the Arctic Ocean off Alaska. The skin of the hair seal is only suitable for making into leather, but there is a layer of fat underneath it which furnishes a valuable raw material for the manufacture of oils and soap. The skins are salted and shipped to America and England. They are easily distinguished from other kinds of commercial hides and skins by the oily appearance of the flesh side.

According to an American Consular Report, the results of the fishing during the season 1913 were satisfactory. The total number of seals captured was 272,965, which were valued at £98,800. The number of skins exported was 212,285, valued at £64,300, of which the United States of America bought 151,355, the United Kingdom 60,754, and Canada 176.

The porpoise, or sea hog, has a very useful hide which, when dressed, makes a tough leather suitable for laces. The hides of other cetaceous mammals, such as the whale and narwhal, are convertible into useful leather. The British "porpoise" laces are generally made from the skin of the white whale (beluga).

Defects of Raw Hides and Skins

A remarkable feature of the leather trade is the great waste due to the careless preparation of a large number of hides and skins. Naturally, owing to their greatly increased value in recent years, there has been a decided improvement, but much loss occurs every day from damage to hides which ought to be avoided. The chief faults are in flaying and curing, but there are other important defects due to natural causes.

Bad flaying may be due (1) to cutting holes in the hides or skins; (2) to "scoring" or "siding" (i.e., cutting into the hide without going completely through), this generally occurring in the flanks or sides which are the most difficult parts of the hide to remove from the carcase; and (3) to mis-shaping the hide, which ought to be left square.

Any or all of these defects may be found in a single hide. Despite the active work of several proprietors of hide markets and the tanners' federations the proportion of badly-flayed hides in England constitutes a serious loss, which, however, may not fall directly on either the butcher or the tanner, for the former may save in wages by employing an inexperienced slaughterman, while the tanner pays a reduced price for the hide.

The losses due to bad flaying and curing in the United Kingdom are mainly attributable to the butchers' preference to kill these beasts in their own back-yard rather than in a public abattoir. Many of these small private slaughterhouses ought to be condemned by the authorities; but very few people outside those immediately interested have taken the trouble to inspect a modern public abattoir where everything is provided to carry on the work expeditiously and hygienically. On the Continent, where the conservatism of traders is not permitted to interfere with the public welfare to such an extent as it is in England, public abattoirs have become quite a feature in many cities, and one of the principal results of the system has been a remarkable improvement in the preparation of raw hides and skins for the tanner. In fact, a mechanical method of flaying has been invented in Paris, and is used extensively at the public abattoirs, by which hides are removed from cattle without a single mark or scratch. The method is known as dépouille mécanique (mechanical flaying) and consists in forcibly removing, by means of a windlass worked by electric power, the portions of hide which adhere firmly to the carcase and which are found over the ribs, the buttocks, and the tail. The remaining part of the hide can be easily removed with the ordinary butchers' flaying knife or with a heavy hammer of special design. The apparatus required to carry out the mechanical method of flaying, beyond the fixtures in the abattoirs where the process is adopted, consist of two lengths of chain to hold the carcase firmly, two special hammers, and one pair of strong pincers; the cost of one set is about £4. Mr. Gaston Tainturier, of Paris, is the inventor of this system, which has added thousands of pounds to the incomes of Parisian butchers.

Figure 1 is from a photograph taken at the Islington (London) Abattoir, where a demonstration of the process was given by Mr. Tainturier in February, 1913.

Naturally, this method cannot be adopted in small slaughterhouses in back-yards, but is readily adaptable to public abattoirs, where practically all of the heavy work is done by electrical power. This exemplifies only one of several advantages of modern abattoirs over private slaughterhouses.

Although it cannot be expected that the English butchers will readily change their prejudice against modern abattoirs, they are slowly but gradually improving the flaying process in view of the high prices paid for perfect hides. The most progressive of the proprietors of the English hide markets are offering money prizes to slaughtermen for the best flayed hides. Strictly speaking, this encouragement should come from the butcher, who receives the benefit of increased prices for hides removed without a scratch. The Tainturier system, however, gives better results, no matter how well the hides are removed with the knife. The method is not patented, and it is open to anyone to adopt it merely for the cost of the apparatus, yet, despite this gain, no butcher outside France and Belgium has yet adopted the method, although the trade is losing hundreds of pounds every week through bad flaying.

Several other systems of improved flaying have been devised, and some of them patented, but very few have been adopted on a practical scale. One of the most useful consists of fixing a safeguard about a quarter of an inch from the edge of the knife; this prevents the possibility of cutting holes into the hide, although it does not, of course, prevent scoring, which is a serious defect in hides made into sole leather. A safe method is to use a sharp knife of hard wood, such as hickory, which has been successfully tried in one of the large American meat-packing establishments. The hides from these abattoirs are generally well-flayed, properly cured, and closely trimmed, with the result that they command higher prices than any other class of salted hides. The quotations for "packer" hides are followed with keen interest by tanners in all parts of the world.

Fig. 1

MECHANICAL FLAYING
(dépouille mécanique)]

Another useful method of preventing damage to the hides by cuts with a knife is that invented by Mr. E. Pim, a Liverpool hide factor. The apparatus used is known as the tail extractor. It is of simple construction, consisting of four pieces of iron riveted together loosely in the shape of a diamond with a clamp attached to secure the tail. The hide is then forcibly removed from the tail and the buttocks by pulling it downward (Fig. [2]). The importance of this operation can be gauged from the fact that by the use of the butcher's knife both of these parts of the hide are often cut very badly.

Fig. 2

PIM'S SYSTEM OF FLAYING

Even the apparently trivial matter of removing the hide from the cheeks and face is economically important, for, unless those parts are removed so as to get the maximum surface, they are only fit to be cut off and thrown in a pit with other pieces and roundings which are made into glue.

Imperfect preservation is another serious form of damage to hides and one that cannot be easily remedied in some of the hot climates. Hides and skins may be simply dried, salted and dried, wet-salted, treated with arsenic solution and dried, brined or pickled with acid and salt; of these methods the last-named is the most effective, but is not practicable, or, at least, has not yet been applied practically to the cure of hides and calf skins. Salt is not available, or is too costly in most tropical countries; hence, Chinese, Indian, Mexican, Colombian, and Arabian hides and skins are generally exported in a dry condition. Even when the hides are dried under the best conditions in a cool and shady place, they are of less value than a fresh or a wet-salted hide, owing to a certain loss of gelatinous matter in softening them before they can be placed in the lime liquors. But it not infrequently happens that hides are dried by exposure to the hot sun, or perhaps in a strong current of air. In either case, the hide is much reduced in value and may be irreparably ruined. The effect of submitting hides to these conditions is that the exterior surface becomes rapidly dry and, naturally, contracted, so that the air or heat cannot reach the interior, which retains moisture. This moist inner layer may be quite thin, but it contains sufficient nutrient to develop putrefactive organisms, so that when the hide is soaked in water it practically falls to pieces. The effect of hot sun or heat of any kind is, of course, disastrous to raw hides and skins, and there have been not a few claims on shipping companies as the result of storing hides near the boilers of ships.

Salt is almost invariably used for curing both hides and calf skins, but though it is a good preservative it has one or two minor defects. It contains too much water, and is liable to contain traces of iron which is inimical to both raw hides and leather in process of manufacture. Common salt is also liable to cause stains which cannot be removed in later processes, and which are even accentuated in the tan liquors. One trade chemist attributes these stains to the presence of calcium sulphate (Ca. SO₄) or gypsum in the salt, which is converted into calcium phosphate by the action of the phosphoric acid in the nuclei of the hide on the sulphate of calcium. Another well-known technical chemist is certain that stains are produced by the growth of bacteria, and to prove his assertion prepared in gelatine several cultures from salt-stained skins. Practical men generally attribute the stains to the presence of blood on the hides or skins at the time of curing, and the majority of the stains are probably due to this cause, although the presence of calcium sulphate as an impurity of the salt would undoubtedly contribute to this defect. Blood contains a percentage of iron, and, with other extraneous matters, should be washed from the hides before salting them.

Fortunately, chemists have lately paid attention to the advantages of the use of pure salt in various industries, with the result that at least two chemically pure products are now available. The use of these salts should be general for the cure of hides and skins, as they are quite dry, and, therefore, easily spread. As a curing agent, they are much more effective and lasting than common salt.

The use of glauber salts (Na₂ SO₄) is recommended by the International Commission for the Preservation, Cure, and Disinfection of Hides and Skins instead of ordinary salt, where the latter is unobtainable. The preparation of a sterilised salt, however, renders its export a practical proposition to almost any part of the world.

Although the loss due to bad curing and flaying is very great, it is quite small compared with the damage caused by natural defects.

The ravages of disease cause a great wastage of hides and skins, as animals infected with anthrax are immediately destroyed and cremated in all civilised countries, while, in Great Britain, foot-and-mouth disease is kept in check by the same drastic method. In many other countries, the infected cattle are isolated, treated with an antiseptic hoof-and-mouth wash and generally cured, as it is a mild fever which soon runs its course, although it is very contagious. The germ of foot-and-mouth disease has not yet been discovered, for the most powerful microscope fails to reveal its presence, but cattle readily show the complaint, as their hoofs and mouths become covered with swollen lesions.

Another kind of fever, known as "tick," was prevalent in the southern part of the United States, but this disease was eventually eliminated by systematically "dipping" the cattle three or four times a year. The cattle "dip" used effectually prevented the ravages of the fly which caused the disease. A similar method has of late years been adopted in South Africa, with the result that cattle-raising in that country is developing rapidly.

Anthrax is due to the presence of bacillus anthracis, a vegetable organism of Siberian origin. Dry Chinese and Russian hides are specially liable to contain the spores of anthrax, and, as the disease proves fatal to workmen infected by it unless treatment with anti-anthrax serum be given in the early stages, hides and skins from infected areas should be disinfected before shipment. The method proposed by Mr. A. Seymour-Jones, which consists in treating hides with very dilute formic acid and one part of bichloride of mercury in 1,000 of water, and afterwards with a saturated solution of salt solution (.02 per cent.) of bichloride of mercury, seems to be the most effective without damaging the hides.

WARBLE FLY

(1) Egg, (2) Larva, (3 and 4) Chrysalides,
(5) Natural form of fly, (6) Magnified fly.

A peculiar natural defect is found in many South American goat skins, especially the Brazilian, which are often badly scratched by the animals rubbing themselves against cactus plants. Although, perhaps, more of an artificial than a natural defect, the scratches caused by cattle rubbing their hides against barbed wire constitute a serious, but easily avoidable, loss. Such a barbarous system of fencing ought never to be used.

A KIP CONTAINING 584 HOLES CAUSED BY THE WARBLE FLY

(The skin belongs to W. D. Mark & Sons, Hide Factors, Newcastle.)

Fig. 3

HOLE IN COW HIDE, MADE BY THE GRUB OF THE WARBLE FLY
(Magnified fifteen times)

The most serious loss in connection with hides and skins, however, is caused by the warble flies, hypoderma bovis and hypoderma lineatum, which lay their eggs on the hides of cattle. It has been a debatable point for some years as to whether these eggs hatched and burrowed their way into the hides from the exterior or were licked and swallowed by the cattle and, after traversing the digestive tract, pierced the hide from the interior. Professor Carpenter, who has been experimenting a number of years for the Department of Agriculture for Ireland, has succeeded in taking a remarkable photograph (Fig. [3]) which proves that the larvae penetrate the hide from the exterior. These develop within the hide and often penetrate to the flesh before they fall out to the ground and change into the fly.

The most effective way of getting rid of the pest is to destroy the larvae, either by cutting them out and crushing them under foot, or by piercing them with a hot needle. No satisfactory dressing has yet been found, but Prof. Carpenter states that sulphur dioxide is effectual, if a good method of applying it can be devised.

While sheep skins are immune from the attacks of the warble fly, they are often damaged by the blow-fly, lice, keds, and ticks; by scab caused by the action of a mite or acarus; and by "cockle," which causes a wrinkled grain. The origin of cockle is not definitely known, but it is a seasonal defect which begins to show on a large number of skins in December and does not disappear until the sheep are shorn in the following spring.

CHAPTER III
TANNING MATERIALS

Tanning materials are derived from the vegetable, mineral, and animal kingdoms.

The vegetable materials used are woods, barks, shrubs, leaves, and fruits, either in their natural state or in the form of extracts. The majority of the minerals have a more or less tanning effect on animal fibres, but the principal are basic chrome salts, formaldehyde, alum and salt. Titanium, iron, cerium and potassium salts also convert skins into leather, but are not yet used commercially.

The animal matters that will convert skins into leather consist of oxidised oils (chamois leather), fats, and brains (crown, Helvetia, or Preller's leather).

Each of these classes of tanning materials has characteristic effects which render them easily distinguishable. The use of combinations of vegetable and mineral tannins has lately increased, and it is possible that the blending of the two classes of materials may produce an ideal tannage for certain classes of leather. In fact, this result is already claimed for a chemically combined tanning material which, according to the American patent, is prepared by the following method: 125 lb. of solid quebracho extract is dissolved in the same weight of hot water and allowed to cool; 16 lb. of commercial caustic soda dissolved in two or three times its weight of water is added, and the mixture agitated about half an hour; 150 lb. of chromium sulphate is then added. In this way an insoluble tannate of chrome is produced, but, on boiling and agitating, it changes to a greenish brown colour and forms a sulphotannate of chrome. The combination of the alum tannage and gambier (a vegetable extract) has been used successfully for years past. Another combination which has given good practical results is the tannage with alum and chrome salts in the manufacture of glove leather.

The vegetable materials containing tannin should be arranged botanically, but the following classification is simpler for practical purposes.

Natural Tanning Materials

1. Barks.—Oak, Hemlock, Pine, Fir, Alder, Khaki, Willow, Cork, Mimosa or Wattle, Babool, Larch, Mangrove, Spruce, Elm, Birch, Pomegranate, Cebil.

2. Leaves, Twigs, etc.—Sumach, Mangrove, Mango, Eucalyptus, Pistacia, Lentiscus.

3. Roots.—Canaigre, Palmetto.

4. Fruits.—Myrobalans, Valonia, Divi-Divi, Cascalote, Mangosteen, Pomegranate, Celavinia, Bablah, Algarobilla.

5. Excrescences.—Gall Nuts, Chinese Galls, Pistacia Galls, Tamarisk Galls.

Tanning Extracts

1. Woods.—Oak, Quebracho, Hemlock, Chestnut, Mimosa, Mangrove, Spruce.

2. Barks.—Oak, Wattle or Mimosa, Larch.

3. Shrubs, Leaves, etc.—Gambier, Cutch, Catechu, Kino, Sumach.

4. Fruits.—Myrobalans, Valonia.

5. Roots.—Palmetto.

Of these materials, only about twenty are of much importance commercially, the principal being oak, chestnut, quebracho, hemlock, valonia, gambier, myrobalans, mimosa or wattle, sumach, mangrove, divi-divi, spruce, larch, and babool.

Oak Bark (quercus robur) is still an important material, but is rarely used alone. The bark from English oaks contains from 8-14 per cent. of tannin (quercitannic acid) as estimated by the impregnation of a standardised hide powder in a given quantity of the tanning material in solution. Owing to its weakness in tannin compared with other materials, oak bark tans very slowly. Used for sole leather, it would not produce the essential quality of firmness and solidity, and it is now customary to use a stronger tanning material, such as valonia, or valonia extract, or gambier in the latter stages of the process. This is the nearest approach to the pure oak bark tannage of former days, and, if carefully regulated, is a great improvement on the old method.

If dressing hides and calf skins required for boot upper leather are bark-tanned, the tannage is often completed in a sumach liquor, the object in this case being to lighten the colour so that the leather can be dyed evenly.

In England, oak bark is harvested in April and May, when the sap rises in the tree. Rings are cut round the tree soon after it is felled and the bark is peeled from the tree with a special tool which is forced between the bark and the wood. It is peeled in narrow strips about 3 ft. in length, and on delivery to the tannery is stacked in huge ricks. If harvested in a good, dry condition, the bark is said to improve with age, although analytical tests have shown that there is always a certain loss of tannin. An old rick is much darker in colour than a new one, owing to exposure to the air. Coppice bark from young trees is preferred by tanners, as it is free from ross and generally contains more tannin than the rough bark.

In view of the modern demand for materials in extract form, English oak bark would almost certainly be preferred in the form of a concentrated liquid, if the supply of the raw material was plentiful within a limited area. During the last few years it has not met with a ready sale, owing to the large supply of other materials, but it would doubtless regain some of its former popularity if it were prepared in the form of an extract containing about 25 per cent. of tannin. The only oak bark extract on the market is the American chestnut oak (quercus prinus).

Oak Wood is very largely used for the manufacture of tanning extract, especially in Hungary and Canada. The extract contains from 24-28 per cent. of tannin, and is extensively used in the tannage of heavy leathers, as it strengthens the liquors and hastens the process, while keeping the quality of the leather at a high standard.

Valonia (quercus aegilops) is the acorn cups of an oak tree which grows abundantly in Asia Minor and the Greek Archipelago. No other part but the acorn cups is exported. The harvest in Asia Minor takes place in August, when the fruit ripens and the cups can be easily beaten from the trees. They are left to dry on the ground and are then sent to stores in seaport towns, and principally to Smyrna. The drying is still further completed in spacious warehouses, where the cups are spread out and turned over until fermentation ceases. During this process the acorns shrink and are rejected. The cups should be perfectly dried and very hard before export. The Turkish valonia contains from 30 to 35 per cent. of tannin, and is of much better quality than the Greek, which is usually harvested before it is ripe, and, therefore, contains the acorn. As the acorn has practically no tannin value, the Greek valonia contains only 25 to 28 per cent. tannin. There are several grades of valonia, the best going to Russia, Austria, and Italy. English tanners seem to prefer the lower qualities at present, probably because the price is much less than that of the best grade.

The beard of the valonia cup is much richer in tannin than the shell, and, as several of the spines become detached during the storage of the material, there is always a certain quantity of beard (trillo) on offer. This may contain up to 42 per cent. of tannin, but its price is usually the same as that of ordinary valonia. Of late years, very large quantities of valonia have been made into extract at two works in Smyrna. The production of extract will no doubt increase, with a corresponding reduction in the export of the raw material. The great advantages of the extract over the natural cup are its superior strength of tannin (60 to 65 per cent.), easier solubility, uniformity of quality, lower cost per unit of tan, and guaranteed purity.

Valonia is well adapted for the tannage of sole leather in conjunction with oak bark, for it deposits a heavy bloom (ellagic acid), imparts weight and solidity, and increases the resistance of the leather to moisture.

The Chestnut Tree (castanea vesca) probably provides the next tanning material of importance. This must not be confused with the chestnut oak, an American tree which also yields a very useful tannin. The chestnut is indigenous to the South of France and Italy, where the forests have been considerably reduced in size to meet the great demand for this popular tanning material. The greater part of the denuded forests have not been replanted with the chestnut, as the land has been put under cultivation whenever possible. A further depletion has been caused by the ravages of an insect, which turns the interior of the wood quite black and renders it unfit for tanning purposes. It will, naturally, be several years before the supply is exhausted, even if no reafforestation is undertaken. As it is the most important tanning material grown in France, and the chestnuts are used as a food, steps may be taken to cultivate the trees on areas unsuitable for agriculture. Liquid chestnut extract contains from 30 to 32 per cent. of tannin, and, when decolorised, gives a light brown colour to the leather. It is rarely, if ever, used alone, but generally in conjunction with quebracho, valonia or myrobalan extracts.

The Chestnut Oak Tree is indigenous to America and the wood yields a very good tanning extract, containing up to 30 per cent. of tannin. This material is the principal tanning agent used in America, where the tannages are roughly classified in three sections: (1) oak, (2) hemlock, and (3) the union (i.e., a mixture of hemlock and oak). American tanners also use other materials to a smaller extent, chiefly for blending with the principal tannins. Quebracho and spruce extracts are specially favoured.

Quebracho Colorado is a tree indigenous to South America, the best wood for tanning purposes being found in the Gran Chaco district in the north of Argentina, and in Uruguay. The wood contains from 17 to 22 per cent. of tannin, and is so hard and heavy that it sinks in water. In fact, its name is derived from two Portuguese words meaning "axe-breaker."

After felling the trees, they are cut up into logs about 4 ft. in length and either exported in this state to Hamburg, Havre, and Liverpool, or sent to the numerous factories in close proximity to the forests to be made into extract, in which an enormous trade has of late years been developed. Very little of the natural material is now used, as, even after cutting the wood into chips, the tannin is extracted only with great difficulty, whereas the extract can be treated with sulphites, alkalies, or neradol (the artificial tannin) to render it easily soluble, besides which the concentration of the material raises the percentage of its tannin to 65 or even 70 per cent. Owing, perhaps, to faulty preparation, this tanning extract was not well received at first, but it is now among the principal tannins and increases in importance every year.

Myrobalans is the unripe fruit of an Indian tree (terminalia chebula) and contains from 35 to 40 per cent. of tannin which gives a light colour to leather. This material is useful both for light and heavy leathers, but is generally used in admixture with other tannins. It deposits much bloom (ellagic acid) and is largely used for brightening the dark colour produced by other tannins. A large quantity of this material is now made into extracts, which are more convenient to handle and more uniform in strength of tannin. Natural myrobalans have the appearance of shrivelled nutmegs, except that they are yellowish in colour; they are very hard and require a special milling machine to reduce them to powder. The quality of myrobalan nuts varies in different districts, the best being Bhimlies and Jubbalpores.

Sumach is a valuable tanning material, and is used for a large proportion of the light and fancy leathers. It is a small bush plant which grows in Italy, Spain, Southern France, America, and Algeria, but of the numerous varieties the Sicilian (rhus coriaria) is by far the most important. Sumach is one of the few materials cultivated on an extensive scale; most tanning materials are derived from natural sources and, chiefly owing to the length of time before trees reach maturity, it would not be a paying proposition to cultivate them. The sumach shrubs are propagated from small cuttings and the leaves can be picked at the end of the first year, but it is better to allow the shrubs to become more firmly established before stripping them. The leaves are dried and sometimes exported whole, especially for the use of the silk manufacturers in Lyons; but they are more often ground to a fine powder. All sumachs should be ventilated to remove foreign matters and all traces of iron, which would cause dark bluish stains on the leather. "Ventilation" is effected by passing currents of air, preferably with a fan, through a narrow room, when the pure sumach is sent forward, while the heavier particles of dirt and small pieces of wood remain behind. Sometimes the process is repeated, and the best brands of sumach are generally described as "pure, extra ventilated." As far as possible, the male plants (mascolino sommacco) are cultivated in Sicily, where the best sumach is grown. Female sumach (femminello sommacco), grown in parts of Italy, is weaker in tannin than the male, but is rarely sold separately. The serious amount of adulteration formerly practised by the admixture of inferior plants, and particularly of lentisco (pistacia lentisco) led to the Italian Government taking strong action a few years ago, and it is now possible, for a very small sum, to have any consignment inspected and analysed by the Government. Lentisco is now sold separately and is used for common work.

Sumach has been successfully introduced into Australia, but its development is retarded owing to difficulties of labour, which render competition with the European product almost impossible. An inferior sumach (rhus glabra) is grown in America, chiefly in the State of Virginia. It contains from 15 to 20 per cent. of tannin, and produces a darker coloured leather than Sicilian, the best qualities of which contain 27 to 30 per cent. of tannin.

A useful test for finding out if a sumach has been adulterated is to treat a small quantity with strong nitric acid, which destroys the structure of the leaves. The mass is washed and neutralised with an alkali, when the appearance of the midrib and veins of the leaves of the common adulterants are easily recognised.

Sumach is not so much used for shoe upper leather as it formerly was, but it is the best tanning agent for many kinds of fancy light leathers, such as bookbinding, calf, and skivers (the grain of split sheep skins), moroccos, furniture leather, etc. It is also less subject to the action of the air and gaslight than any other tanning material, and is strongly recommended for tanning purposes by a special committee appointed by the Society of Arts to enquire into causes of the rapid decay of leather bindings. Sumach is very useful for brightening up the colour of leather tanned with darker tannins, and is frequently used for improving the colour of both dressing and sole leather. By itself, it yields an almost white leather which affords a good foundation for the most delicate shades.

Gambier or Terra Japonica (uncaria gambir) is a crude extract of a shrub indigenous to the Malay Peninsula. Nearly the whole of the production is shipped from Singapore. The leaves and twigs are boiled in an iron vessel, and when the mass has become syrupy it is strained through a rough sieve into a shallow tub, where it is cooled. The liquor is stirred while cooling and rapidly thickens. Before it sets, it is cut into 1 in. cubes and thoroughly dried. Good qualities contain from 50-65 per cent. of tannin. An inferior product, called "block gambier," is made by allowing the syrupy mass to set in large blocks weighing about 2 cwt. each. These are packed in coarse matting. The strength of tannin varies from 30 to 40 per cent. Gambier is a good tanning material, but its use has been declining for some years past owing to its being frequently adulterated with sago and other farinaceous plants. However, a pure gambier extract, manufactured on the latest scientific principles, has been placed on the market, and there will undoubtedly be a revival of the use of this valuable tannin. This pure gambier is prepared at Asahan, in Sumatra, and is guaranteed to contain a minimum of 38 per cent. of tannin.

Gambier can be used to advantage in keeping up the strength of bark liquors in the tannage of sole leather and hastening the process, while it may be used alone for the tannage of boot upper leather and dressing hides. It produces an exceptionally mellow and plump leather. It is preferable, however, to complete a gambier tannage with a little oak wood or quebracho extract, in order to fix the tannin principle of gambier, which, perhaps on account of its viscosity, does not readily combine with the fibres of the skin.

Mangrove or Mangle, a tree found on the coasts of several tropical countries, yields a useful bark for tanning purposes. At low tide, these trees show their great arched roots standing high above the ground. The best varieties, the ceriops species, are found in the East Indies and Bengal, and the bark of these is said to contain sometimes nearly 40 per cent. of tannin. Other varieties contain from 15 to 25 per cent. The bark is generally made into a solid extract, or "cutch," in which form it contains more than 60 per cent. of tannin, It is useful to blend with other materials, such as oak wood, chestnut, and quebracho extracts, but used by itself it imparts a strong reddish colour to the leather. Some of the Indian varieties are used as dyeing materials, and act as a satisfactory mordant in dyeing leather a dark shade.

Mimosa or Wattle trees, which belong to the acacia species, yield bark rich in tannin. Australia is the native country of several varieties, including the Black Wattle (acacia pycnantha), the Golden Wattle (A. longifolia), and the Green Wattle (A. decurrens).

The bark contains from 20 to 45 per cent. of tannin. The cultivation of wattle in Australia seems to have declined, owing to the high cost of labour and inability to compete with the mimosa bark imported from South Africa, where it is cultivated on a very large scale and where labour conditions are more favourable for the growers, as is clearly shown by the fact that the wattle growers in Australia successfully petitioned the Government a short time ago to place a duty of £1 10s. per ton on the imported bark.

The introduction of the industry into South Africa was quite an interesting adventure. A Mr. Vanderplank brought the seeds from Australia to England about seventy years ago, and afterwards took them to South Africa, where, in recognition of certain services a few months after his arrival, he was granted a farm by the Dutch Government. He then planted the seeds of the black wattle, which grew so well that it was only a question of developing the industry. It was some years before any African bark was exported, and only £11 worth was shipped in 1886. In 1911, the exports had risen to £288,000.

Wattle trees can be grown on soil that is unsuitable for agriculture, and there is every prospect of the industry expanding in South Africa, where a factory has lately been established for the purpose of converting the bark into an extract, which, it is said, will contain between 50 and 60 per cent. of tannin. By far the greater proportion of wattle bark is still exported in the natural form, ground or chopped, and packed into bags weighing about 1 cwt. each. Before the European War nearly the whole of the bark was shipped to Hamburg, English tanners taking very little interest in it, although it was largely used by German tanners. But since the supplies of the materials favoured by British tanners have become somewhat restricted, attention has been drawn to the value of mimosa bark.

Divi-Divi (caesalpinia coriaria) is the dried pods of a Central American tree. It has also been successfully cultivated in India. The pods are rich in tannin, containing anything from 40-50 per cent., but its value is discounted by its liability to fermentation, which, however, may be checked to some extent by the use of antiseptics, such as carbolic acid, formaldehyde, or by the addition of synthetic tannin, neradol. If this tendency to fermentation and oxidation of the colouring matter could be checked completely, divi-divi would be a valuable material, as it makes a firm leather of good colour. When dried, the pods curl up in the shape of the letters S and C. The tannin is found in the husks of the pod. The seeds, which contain no tannin, are so hard that it has not yet been found profitable to extract the oil from them. Very similar tanning materials to divi-divi are cascalote, indigenous to Mexico, and algarobilla (caesalpinia brevifolia) which grows in Chili. Cascalote is chiefly used by Mexican tanners and is rarely exported. Algarobilla is not available in large quantities, otherwise it would be largely used in Great Britain, as it does not ferment so readily as divi-divi, and is even richer in tannin.

Celavinia (also spelt celavina and cevalina) has been on the English market since 1905, but has only lately been sold in large quantities. The scarcity of some of the popular tanning materials since the outbreak of the European War resulted in enquiries for materials that were very little known, and celavinia has proved worthy of attention. It consists of the seed pods of the tree caesalpinia tinctoria, which grows abundantly in certain districts of Central and South America. The pod is from 4 to 6 in. long and is flaky when dried. It contains 30 to 32 per cent, of tannin of the pyrogallol class, and gives a very light-coloured and almost white leather. It is the only pyrogallol tannin which does not deposit bloom, or ellagic acid, on the leather. It may be used as a substitute for sumach in tanning, but has not the same bleaching effect in the retanning process. A tanning extract of celavinia would be useful for some classes of light leathers, where paleness of tint is important. It is difficult to make a second extraction of tannin in the case of the natural material, as, after the first extraction, it forms a soft pulp, through which water will not easily percolate.

Hemlock (abies canadiensis) is an important tanning material, both the bark and the wood being extensively used in America. The wood is now generally converted into extracts in factories built near the principal forests. Of late years, this extract has been imported into the United Kingdom in fairly large quantities, in order to produce a cheap red sole leather to compete with the American hemlock-tanned leather. It contains only about 25 per cent. of tannin, but its value is increased by its contents of insoluble non-tannins, which give weight and solidity to the leather. Hemlock really gives a strong, durable leather, but in America the practice of using artificial weighing materials, such as glucose and Epsom salts, with a reduced quantity of tanning material, has considerably lowered the value of this leather.

In addition to the materials described, there are several of minor importance which can only be briefly mentioned.

Larch Bark is obtained from the tree larix Europea, which is found in Scotland and North Europe. It contains 10-12 per cent. of tannin, which gives a light colour and pleasant odour to leather. Scotch basils (sheep skins) are tanned with this bark.

Birch Bark, from the white birch, betula alba, is another aromatic tanning material. It contains only about 5 per cent. of tannin, and is, therefore, generally used with other tanning materials. It contains a tar which imparts an agreeable scent to the leather that protects it from the ravages of insects. In conjunction with willow bark (salix arenaria) it is used in the tanning process for the real Russia leather. An oil containing the scent can be extracted from the birch bark by dry distillation, and this extract is sometimes used during the dyeing process, in the manufacture of imitation Russia leather, which, however, only retains the scent for a few months, whereas the real Russia leather has a permanent odour.

Canaigre (rumex hymenosepalum) is the tuberous root of a dock plant indigenous to Mexico and the Southern States of America. It is fairly rich in tannin (25-30 per cent.) and yields a moderately firm leather. It contains too large a proportion of starch, however, and cannot be described as a really satisfactory tannin. Moreover, it is not harvested economically and the only way to make a satisfactory tannin of it is to convert it into extract and remove the starchy matters near the source of supply, if anyone dare take the risk of establishing a factory in Mexico.

Bablah or Babool (acacia arabica or acacia vera) grows in India, Egypt, and the Sudan. The bark of the babool tree is one of the principal tanning materials used in India for hides, calf, and sheep skins, which are sent in large quantities to Great Britain in a rough-tanned state and dressed there. It contains 15-20 per cent. of tannin, which readily oxidises in the leather in contact with light, turning into a bright pink colour. It also seems to weaken the fibres of animal tissues, and, for that reason, babool-tanned leather was condemned by the Society of Arts Commission on Bookbinding.

The pods contain from 20-30 per cent. of tannin and give a mellow and plump leather similar to that produced by gambier. The bleaching of the material is troublesome, and it is probable that its use would be increased if the tannin were prepared in the form of extract.

Cutch is a crude extract made from the Indian tree acacia catechu. This is the real cutch, as distinguished from the mangrove "cutch." It is very rich in tannin (50-60 per cent.), but contains a large proportion of insoluble matter and is, therefore, very little used for tanning. It is well adapted for the dyeing of dark colours or black with mineral strikers, such as chrome and iron salts; but its chief use is for tanning fishermen's nets, which it renders waterproof.

Commercial tannic acid, used for medicinal purposes, is prepared from galls or excrescences on oak trees growing in Asia Minor. These galls are caused by an insect (cynips) puncturing the small branches and producing abnormal growth in the perforated parts. The acid is gallotannic, which, if used for making leather, would produce a soft, spongy, and nearly white leather. This tanning material is used a little by Near Eastern tanners, but the result is unsatisfactory.

Classification of Tanning Materials

Tanning materials are divided into two main classes: (1) Pyrogallol, (2) Catechol. The pyrogallol tannins give a bluish-black colour, and the catechol tannins a greenish-black, with iron salts. Bromine water does not precipitate pyrogallols, but causes a precipitate with catechols. Pyrogallols yield ellagic acid (called "bloom" in the trade), which improves the waterproof qualities of leather. On the other hand, catechols contain a large proportion of insoluble reds, or phlobaphenes, which are deposited between the fibres and thus give solidity to the leather. Pyrogallol tannins give a light coloured, soft leather, and can be used alone satisfactorily; but heavy leathers, such as sole and belting, need a blend of both kinds of tannin. The pyrogallol tannins include sumach, chestnut, myrobalans, divi-divi, oakwood, algarobilla, chestnut oak, willow, and galls. The catechols include quebracho, gambier, hemlock, mimosa or wattle, mangrove, larch, birch, canaigre, and cutch. Oak bark and valonia contain some of the properties of both classes of tannins.

There are sub-divisions of these two classes, arranged according to chemical tests, by which one tanning material can be distinguished from another.

Tanning Extracts

The manufacture of extracts from vegetable tanning materials has increased so rapidly of late years that the process of tanning has undergone radical changes; and, whereas the tanner was limited to three or four materials thirty years ago, he now has the choice of about twenty good materials. These tannins can be suitably blended to produce first-class leather. The processes in extract manufacture are few. The wood, bark, or fruit is broken up into small pieces and macerated in hot or cold water. The concentration of the liquid is done in vacuum, or in an evaporator. The latest method is to treat the tan liquor in a "triple-effect" evaporator (Fig. [4]), the object of using three compartments being to economise in steam. This apparatus makes liquid extracts; where a powdered or crystal extract is required, the liquid is afterwards treated in a vacuum drying apparatus. Some extracts contain a lot of colouring matter and insoluble substances. To overcome this defect, they are clarified with blood albumen, sulphites, casein, or acetate of lead.

FIG. 4.—TRIPLE-EFFECT EVAPORATOR
(Blair, Campbell & McLean, Ltd.)

Synthetic Tannins

The discovery of a synthetic tannin, in 1911, by Dr. Stiasny, who was then an assistant in the Leather Industries Department of Leeds University, created a great deal of interest in the leather trade, and can certainly be regarded as a triumph of the application of chemistry to industry. It was thought at first that these tannins might play as important a part in the leather trade as the synthetic dye-stuffs have, but it is now generally believed that this will not be the case. Their use is likely to be as an aid to tanning, rather than as a complete tanning agent, although it has been found practicable to use them for one or two classes of light skins, where it is essential that the colour of the leather should be nearly white.

The original patent was taken out in September, 1911, in Austria, the native country of the inventor, but the patent rights have also been protected in other countries, while the manufacture and sale of the product passed into the hands of a large German dye firm, who have since taken out several patents for other synthetic tannins. The original tannin is produced by treating a sulphonated phenol with formaldehyde. A patent had been taken out several years before for the use of formaldehyde in tanning, but this expired early in 1911; many patents had also been granted for sulphonated phenol preparations, chiefly as disinfectants, but it was left to Dr. Stiasny to discover the value of combining the two chemicals by the process of condensation. The preparation, first known as "neradol," is now made in England under licence, but, since the war, its cost has been more than doubled, so that it is unlikely to replace natural tanning materials to any great extent.

Formaldehyde itself has certain properties which are harmful to leather, and it must be used with extreme caution and in small quantities to avoid these defects. It is used in the leather trade chiefly for keeping up the substance of hides during the tanning process, and thus causing a rapid absorption of tannin. At the beginning of the tanning process, the liquors are acidified, preferably with a weak organic acid, which causes the fibres of the hides to distend. It is at this stage that the formaldehyde is used. This method, which cannot improve, but may easily damage, the leather, is almost entirely confined to the Continent. Formaldehyde has a hardening and tanning effect on animal tissues, and leather treated by this process often has inferior wearing qualities.

In the case of the artificial tannin, this property of formaldehyde is to a large extent modified by the chemical reaction with a sulphonated phenol, the addition of which also increases its tanning effect; but, while the tannage is very rapid, especially in the case of light skins, leather produced solely by means of artificial tannin has a slight tendency to dryness after being in stock for some time.

No doubt, however, methods will be found to overcome initial difficulties, and various liquors will be prepared to meet different requirements. The question of price remains the deciding factor as to its use on an extensive scale, for, while it is so high, natural tanning materials will be preferred, except in a few special cases. According to the hide-powder method of tannin analysis, Neradol contains about 30 per cent. of tannin, but there are many natural tannin extracts containing nearly double the amount of tannin at nearly half the price of the artificial tannin; the latter, however, has a more rapid action and also produces a nearly white leather. Another advantage of Neradol is that it prevents drawn grain, so that, if raw hides be treated with a small quantity before tanning, stronger vegetable tan liquors may be safely used to hasten the process. In the manufacture of sole leather, for example, limed hides, after washing in water, may be suspended in a solution of Neradol containing 3 to 5 lb. per 100 gal. of water for twelve to twenty-four hours. This quantity produces a slight tanning effect, the hides are thoroughly delimed, and strong vegetable tan liquors may then be used to complete the tannage without the grain of the hide being drawn or dark in colour, as would be the case if the hides were not first treated with the artificial tannin.

Neradol is also said to be an effective bleaching agent for tanned leather in a 5 per cent. solution for a few hours, without any loss of weight.

This property may also be utilised in the production of chrome leather, where a whiter colour is required than that produced by the ordinary chrome tannage. For this purpose it may be used in a pickling liquor before the one-bath process, or in the second bath of the two-bath tannage.

For dressing wool and fur skins, the synthetic tannins are much superior to the alum and salt process.

CHAPTER IV
LEATHER WORKING MACHINERY

When it is considered that the construction of machinery for the leather trade had barely started thirty years ago, the wonderful variety and utility of modern machines are remarkable, and it is a moot point whether engineering science has not played as great a part as, or even greater than, applied chemistry.

Excepting the bark mill, various kinds of tumblers, the fulling stocks, glazing and rolling machines, there were practically no efficient mechanical aids to lighten the exceedingly laborious operations incidental to leather manufacture two decades ago; but so many improvements have lately been made in the construction of machinery for practically every operation in the trade that most of the machines require very little skill to work them, and can be operated by intelligent youths after a few weeks' experience.

The change has been of great benefit to the health of the workers, for the continual stooping over beams and sloping tables, combined with the arduous nature of the work, was very injurious. The reputation that tanning had as a healthy occupation was due more to the work of the labourers than that of the skin workers. (The old-fashioned lime-yards and tan-yards were generally in the open, whereas modern tanneries are roofed.)

Leather trades machinery was not a success at first, probably because it was very difficult to get the necessary information from leather manufacturers. However, as the engineers gained more experience of the methods of leather-making, the defects were gradually remedied until it may be truly said that the machines now reach a high state of perfection. It was no uncommon thing for workmen to lose a finger or two in a machine, but such accidents are now rare, owing to improvements in the construction of the machines.

Most of the machines used in the leather trade are of the cylinder type, the raw skins or leather passing between two rollers, of which the upper one performs the operation while the lower one helps to draw the material through the machine. To prevent accidents and control the working of machines, a third roller is often used, which serves to "feed" the leather or skins to the working cylinders. Of this type of safety roller, the Seymour-Jones attachment to the shaving and buffing machine is of great importance.

Fig. 5

SHAVING CYLINDER

The operations of the tannery, which are performed by cylindrical machines, are dehairing, fleshing, scudding, samming, shaving, scouring, striking-out, setting, boarding, buffing, graining, printing, embossing, and blacking or colouring. The working cylinders usually vary according to the character of the operation, although one or two types may be used for at least three different operations.

Where cutting or paring is done, the working cylinder is fitted with brass blades, or steel blades backed with iron. The blades are spiral in some machines, and are so arranged that half of them converge to the left, and half to the right (Fig. [5]). When in work, this type of cylinder not only performs the operation for which it is specially intended, but also stretches the leather outward, by reason of the arrangement of the blades or knives. The blades overlap one another to obviate marking, for if the blades met exactly at the centre they would make a line on the leather. Figure 6 shows another arrangement of knives for the process of buffing.

Fig. 6

BLADED CYLINDER FOR "BUFFING" LEATHER

Fig. 7

BAND-KNIFE SPLITTING MACHINE

The most important machines outside the working cylinder type are the splitter, and the glazer. There are several kinds of splitting machines, but the band-knife machine (Fig. [7]) is the most largely used. This is a veritable triumph of the engineer's art, for it is possible to make five or six layers, all about the same size, out of one hide, although leather is only split once or twice as a rule. Of course, sole, belting, and other thick leathers are not usually split. The invention of the belt-knife splitting machine revolutionised the leather trade, and there would undoubtedly have been a great shortage of leather without it. Formerly, all the levelling and reducing of substance was done by paring off quite small pieces with the shaving knife (Fig. [8]), a difficult and laborious work. These parings were only suitable for pulping and compressing into leather board; but now the flesh splits removed by the machine can be curried, enamelled, printed, or rolled to make serviceable leathers, although, of course, not nearly so good in quality as the top or grain split. The main working part of the splitting machine is an endless steel knife which passes round two wheels placed at opposite ends of the machine. The leather is drawn to the knife through two rollers, of which the lower one is in sections to allow very thick parts of the hide to pass through the machine. It would need a large volume to describe in detail all the different machines used in the leather trade; the constructional details of only one machine can be given, and, in view of its importance, the shaver is selected. Reproductions of other machines will appear in succeeding chapters.

Fig. 8

SHAVING KNIFE

Nearly every leather trades' engineer constructs shaving machines, but the Howard-Smith is described here, not because it is the most popular (unfortunately there is a decided preference for low-priced machines), but because it is one of the best from an engineering point of view, and because several improvements are embodied in its construction.

Fig. 9

SHAVING LEATHER
(Old method)

This machine consists of nearly one hundred parts and each is made of the best material available. The advantage of this is obvious when the question of repairs is fully considered. The first Howard-Smith machine made has been running more than four years, and has not cost the owner a penny for repairs, beyond, of course, the expense of replacing the blades of the working cylinders; whereas it is no uncommon occurrence for a cheap machine to be thrown on the scrap heap after a few years' wear. It is always advisable, therefore, to buy machinery of the best grade.

bet, pp. 56 & 57

Fig. 10

DRAWING OF SHAVING MACHINE

Figure 10 represents a drawing of the shaving machine, A being the side view, and B the front. The work of the draughtsman generally appears to the uninitiated to border on the miraculous; he is often the designer and architect of the machine, and his work is certainly interesting and skilful.

Many of the heavy parts, such as main castings, pedestals, etc., are made in the foundry, which may be part of the leather trades' engineer's works if he is in a large way of business. The finer parts, those which might be termed the fittings, are made in the turnery department; while the machine is assembled in the fitters' shop.

Figure 10 A shows the side, and 10 B the front construction of the shaving machine. The figures indicate, by following the arrows, the principal parts of the machine, which are shown in detail in sectional tracings. For example, T. 65, of which no working parts are shown in the diagram of the complete machine, is reproduced in detail in a separate drawing shown in Figure 11. Each part of the machine is numbered and entered in a stock-book.

In describing the principal parts indicated in Figure 10, it will give an idea of the assembling of the machine if a beginning be made with the main iron castings. These comprise the main bed (64), two side frames (62), and the front frame (58). The side frames are strengthened by the ribs which form the edge, and which are about three times as thick as the body of the casting. The object of the front frame is to support the foot lever (59), the rocking frame (57) carrying the rubber roll (79), and the wooden roof (75) over which the leather is passed. The spring (76) pulls back the rocking frame (57) when relieved by the operator removing his foot from the lever (59). The long spring (77) lifts up the foot lever (59) when the latter is released.

The pullies (73) are connected with the knife cylinder which shaves the leather. The cylinder is obscured by the wheel-guard (65) and is, therefore, shown separately. This cylinder is comprised of a shaped piece of steel (turned out of solid metal bars of 4-3/4 in. diameter) into which spiral steel blades are caulked with copper or brass. When turned, the body of the cylinder is 4-5/8 in. in diameter, but the parts forming the bearings are reduced to 1-1/2 in. The number of blades is twelve, fourteen, or sixteen, according to the kind of leather shaved, and to the choice of the operator.

It is interesting to note that these blades are now being made in Sheffield, although, before the war, they had to be imported. The knife guard (65), shown in detail in Figure 11, is an ingenious contrivance which prevents the operator's hands being drawn into the machine. It consists of an automatic shutter worked by a steel chain from the foot lever. Figure 11 a represents the shutter closed down on the knife with the rubber roll, on which the leather is carried to the knife, at a safe distance from the shutters. Fig. [11] b shows the position when the machine is shaving the leather, the guard being clear and the rubber roll engaged with the knife.

Fig. 11.

In order to sharpen the blades of the cylinder, a carborundum wheel is fixed in close proximity, its position being indicated in the drawing by the wheel cover (67). A bracket for feeding the wheel to the blades when grinding them is shown at 66. When grinding the blades, the saddle (68) carries the wheel backwards and forwards across them. A special feature of the saddle in this particular machine is the double-thread screw, one a right hand, and the other a left hand. The saddle (68) is actuated by a "swimmer," as the makers term it, which engages, say, first the right-hand thread; when the saddle has travelled to the end of its movement the "swimmer" automatically enters the left-hand thread, and the saddle is rotated in the opposite direction. The "swimmer" can be disengaged instantaneously. A brush (55) is fixed near the cylinder to remove any leather shavings adhering to the blades. It also acts to some extent as a fan, and, by creating a current of air, carries the leather dust away from the operator. A trough is filled with water to catch the dust from the carborundum wheel, while the knives are being ground. The trough should be cleared out and refilled with clean water from time to time. It is essential that no dust from the grinding wheel comes into contact with vegetable tanned leather required in a natural or colour finish, otherwise it will cause iron stains, which are difficult to remove without damaging the leather. For this reason, the knives should not be ground while this class of leather is being shaved.

An important detail of the machine under description is a trueing device. Knives are often roughened owing to the carborundum wheel wearing irregularly. The trueing device keeps the wheel perfectly true by means of a diamond held in the end of a screw (78). Another ingenious arrangement (patented) is a spring (79a) placed at the back of the rubber roll (79), which enables the roll to spring back when the leather, or any part of it, is too thick for the cutting cylinder.

A unique advantage of the Howard-Smith machine is that it is ball-bearing throughout. The main driving shaft revolves on four massive ball-bearings in case (71). The pullies are firmly fixed to the driving shaft with keys or feathers. Afterwards the pullies are machined, so that the whole shaft with its pullies is perfectly balanced, and the machine runs smoothly without vibration.

The bladed cylinder is likewise mounted on four ball-bearings. The intermediate driving shaft (70), which is mounted on two ball-bearings, is connected with a large drum shaft (70a) which, in its turn, sets the carborundum wheel in motion.

Fig. 12

shaving-machine
(Haley)

Fig. 12 represents another make of shaving machine.

CHAPTER V
PREPARATION OF HIDES AND SKINS FOR TANNING

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.

Fig. 13

DRUM TUMBLER

Fig. 14

FALLER STOCKS

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.

Fig. 15

TANNER'S BEAM

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.