Animal Proteins Part 15

_J.S.C.I._, 1913, 775.

Patents:--Austrian 58,405.

German 262,558, Sept. 12, 1911.

French 451,875, Dec. 13, 1912; 451,876, Dec. 13, 1912; 451,877, Dec. 13, 1912.

SECTION VI.--COMBINATION TANNAGES

The formation of leather being due to the adsorption of colloidogenic substances at the interface of the tanning liquor and the hide gel, there is the obvious possibility that several such substances may be used simultaneously, and that the resulting leather may be due to the combined effect of these substances. Indeed, the average vegetable tannage consists of such a combination tannage, each tanning material contributing its own individual tannin and characteristic astringent non-tannins. There is evidently also the possibility that the different _types_ of tannage discussed above might be used either simultaneously or successively, and that a leather might be obtained which combines to some extent the qualities of each of the types in combination. It is such a case that is generally called a "combination tannage." There are many conceivable combinations, and in this section will be chiefly discussed a few which have demonstrated some commercial possibilities.

Some of these have already received notice in the preceding sections.

The manufacture of curried dressing leathers is a combination of vegetable and fat tannages. The manufacture of waterproof chrome uppers ill.u.s.trates a combination of chrome and fat tannages. The use of "syntans" in conjunction with vegetable tanning materials is also a combination tannage. The case of chamois leather is possibly a combination of aldehyde tannage with fatty acid tannage. Two-bath chrome leather is a combination of chrome, sulphur and fat tannage.

Formaldehyde and vegetable tannage is also a known possibility. It is clear that there are possibilities of endless complexity, and that what normally may appear as a simple tannage is in reality a very complex combination tannage. From this standpoint one might instructively consider the successive adsorptions involved in a goatskin tanned first with syntans, then with oak bark, "retanned" in sumac, mordanted with chrome, dyed with coal-tar dyestuffs and finally oiled with linseed oil.

It will be easily seen that in a very strict sense nearly all tannages are combinations.

Usually, however, the term "combination tannage" is confined to those cases where the main tanning agents not only differ in type, but where none are in predominant quant.i.ty. A typical case is that of "semichrome leather," in which a vegetable tannage is succeeded by a chrome tannage.

E.I. tanned sheep and goat skins are rather heavily "stripped" of their vegetable tannage and heavy oiling, by drumming with warm soda solutions, and after was.h.i.+ng with water are chromed with the one-bath process; they are neutralized, dyed, fat liquored and finished for glace upper leather.

In a precisely similar way kips and split hides which have received vegetable tannage are stripped and retanned in chrome and finished as for box calf, of which they are a good imitation. Such vegetable-chrome combination tannages possess many of the properties of chrome leather.

To chrome the pelt first and afterwards to subject it to vegetable tannage is also an obvious possibility, but has not yet been made a commercial success in this country, but has been increasingly used in the U.S.A. during the War.

Another typical case of combination tannage is the dongola leather produced by the use of gambier and of alum and salt. This is a vegetable-alum combination, and yields a good quality leather for light uppers, gloves, etc. Goatskins for "glazed dongola" are paddled tanned in gambier liquors, and alum and salt are subsequently added. They are tanned in 24 hours, well washed, and are fat liquored without ageing.

The E.I. tanned skins may also be stripped with soda, and retanned in alum and salt, using flour also if desired. Dull dongola are first tawed and then retanned in gambier liquor. "Suede" and "velvet calf" are also tawed and retanned with gambier.

Yet another case of combination tannage is that of sheepskins for glace uppers, which are first tawed thoroughly with alum, salt and flour and dried out for sorting, and are then retanned in chrome by the one-bath process, and finished as usual. Closely related to this is the method of "pickling" in alum and salt and then chrome tanning.

Another case is the combined one-bath, two-bath method of chrome tanning. The goods are chromed by a one-bath liquor containing dichromate (say 2 per cent.), and then pa.s.s into a reducing bath. There is not much advantage in such procedure, however.

From a strictly commercial point of view the "dongola" and "semichrome"

leathers have proved the most successful combination tannages, but there seem to be possibilities in combinations of the vegetable tannins with synthetic tanning materials.

Many other substances are known to tan, _e.g._ iron salts, cerium salts, sulphur, quinones, fatty acids, the halogens, etc., etc.; hence there is always the possibility that new useful combination tannages may be discovered.

REFERENCES.

Bennett, "Manufacture of Leather," pp. 243, 374-5.

Procter, "Principles of Leather Manufacture," p. 236.

SECTION VII.--THE EVOLUTION OF THE LEATHER INDUSTRY

The leather trades are amongst the oldest of all industries, but their evolution has been much more rapid during the last two or three decades than at any other period of their history. The European War, moreover, has caused the commencement of another period of rapid development, and it is the aim of this section to point out some of the princ.i.p.al lines of change which have already become apparent.

Many of these lines of evolution in the methods of manufacture have been previously discussed in their appropriate sections. They may all be summarized as attempts at more economical production. Prominent amongst them is the persistent effort to attain quicker processes. During the last twenty-five years the time necessary to produce the heavy leathers has been reduced from 12 months to as many weeks. The tendency is to reduce the time further still, but this is of course increasingly difficult to accomplish. On the other hand, it is more urgent to strive in this direction than ever, because a needless week involves more capital lying idle than ever before. Moreover, as most leather factories are now large works, a saving even of 24 hours has become a serious item in economic production. Hence in liming, bating, tanning, drying and in warehousing there are increased efforts to make a quicker turnover.

A good ill.u.s.tration of this "speeding up" in modern tanneries is the adoption by all large factories of much more rapid methods of extracting tannin. On the old press-leach system liquors may be percolating through the material for possibly a fortnight. The extract manufacturer reduces this operation to about two days. Steam generated from the spent bark is used to heat the extracting vats, and to work a vacuum pan or evaporator whereby more water can be used and a more complete as well as a more rapid extraction obtained. The evaporator also makes easy the preparation of the strong liquors used in modern tanning.

Hand-in-hand with quicker production and manipulation are the attempts to obtain a larger turnover. It is realized that the big business attains cheap production. Even before the war the smaller factories were disappearing. A small tannery must now either extend or close down. This has been better realized in the heavy than in the light leather trades.

In the sole leather tanneries very often many thousand hides per week are put into work, but in the glace kid factories there is nothing yet to correspond to the output of American glace factories, which sometimes reaches three or four thousand dozen a day.

Another very prominent feature of factory evolution is the increased use of labour-saving machinery. This practice has been in operation for a considerable time, but with marked acceleration during the last few years owing to the labour shortage occasioned by military service. This development of machine work has largely dispensed with that labour which involved any skill or training. The journeyman currier is now practically extinct. In the beam house, too, fles.h.i.+ng, unhairing and scudding are rapidly becoming machine instead of hand operations. Many devices are now being adopted also which reduce the quant.i.ty of unskilled labour needed. Instead of "handling" the goods from pit to pit, modern tanneries aim at moving the liquors. Thus in the "Forsare"

and "Tilston" systems of liming, hides are placed in a pit and lie undisturbed until ready for depilation, the soak liquors and lime liquors being supplied and run off just as required, whilst these liquors are agitated as often as desired by means of a current of compressed air. This agitation replaces the "handling" up and down once practised. In the tanyard proper the same tendency is at work, "rockers"

are increasingly preferred to "handlers," and an inversion of the press leach system permits the exhaustion of tan liquors by a gravity flow, and so avoids the handling forward from pit to pit. There is also a tendency to install lifts, overhead runways, trucks on lines, motor lorries, etc., to replace carrying, barrowing, carting, etc., and so to arrange the tannery that the minimum transport is needed.

All these lines of evolution involve more intensive production, and necessitate much more careful supervision. It is not surprising, therefore, that the industry now feels that scientific oversight and administration are essential. A dozen years ago the trade chemists were largely unqualified men, whose work lay solely in the laboratory, and consisted mainly in the a.n.a.lysis of materials bought. To-day all large tanneries have qualified chemists, and it is realized that they are the practical tanners. Their function is so to control the manufacturing processes that all waste is avoided, and so to correlate and co-ordinate the manufacturing results with the a.n.a.lytical and experimental records of the laboratory, that constant improvements are made in the methods of production. The extended use of machinery, and the necessity for economy in coal and power, give the engineer also very large scope for useful work. Modern business conditions, moreover, have made necessary more skilful clerical work and accountancy in the large offices of a modern tannery.

In the creation of cordial relations.h.i.+ps between capital and labour in the leather trades, there has been unfortunately little progress. The leather trade is not a sweated industry. Its workers have always enjoyed reasonable hours of work. In most factories an approximate 48-hour working week (involving no night work) has long been in operation. The industry, however, is not one in which high wages obtain. The average tannery worker receives a wage which is never much above the level of subsistence. This is mostly due to the fact that he is usually a quite unskilled labourer, and is therefore on the bottom rung of the labour ladder. In addition to this the work itself is often distressingly monotonous, and makes little demand upon the intelligence of the worker.

The trade consequently offers little attraction to the intelligent labourer. The old system of apprentices.h.i.+p is now quite obsolete, partly owing to the rapidity of the changes in the methods of manufacture, partly to the specialization of labour which results from the development of large factories, and partly also, because to understand modern tanning involves a better general education than most workmen receive. It is indeed frequently difficult to find competent under-foremen for the different departments of the modern leather factory. Until recently leather workers have been either unorganized or badly organized, and their views and complaints have been confused and sporadic, but during the war period there has been a very rapid extension of trade union movements, and consequently a more articulate expression of the demands for "democratization" as well as "a greater share in the fruits" of the industry. In the leather trades, however, the gulf between the unskilled labourers and the wealthy employers is perhaps unusually wide, and there is little disposition on the part of capital to recognize the equity of either of the above demands of labour. Generally speaking, the leather trade firms are not public but private companies. There is absolutely no trace of "co-partners.h.i.+p" or "profit-sharing" schemes, or of co-operative production. There is little recognition that the trades' prosperity should be shared in any way by the workpeople, and still less recognition of any right to a voice in industrial conditions. This condition of affairs has an ominous reaction upon the att.i.tude of labour, which believes that it is producing great wealth but not obtaining much more than subsistence. It is not the function of this volume to p.r.o.nounce a verdict upon the wages question or upon the democratization of the leather trades, but one may be permitted earnestly to hope that if such be the future lines of development, there will be also, as an absolutely essential part of any such schemes, a much higher standard of education amongst the workers, for this is the only satisfactory guarantee that the voice of labour in council will have any practical value, or that higher wages will be at all wisely used by the recipients.

In his instructive and valuable volume on "The Evolution of Industry,"

Prof. MacGregor points out that modern industry has evolved three outstanding types, viz. the Co-operative Movement, the Trusts, and the methods of Public Trading. He also suggests that these types tend to blend. In the leather industry co-operative and munic.i.p.al production are unheard of, but the industry has certainly developed along the lines of the large trusts. Large businesses have replaced small, and later still have formed local federations, which in turn have combined to form the "United Tanners' Federation." War conditions have certainly stimulated evolution towards the trust type. The United Tanners'

Federation has become possessed of powers which were not originally contemplated, such as the purchase and distribution to its members of hides, bark, extract, sulphide and other materials. How far some of these arrangements will be permanent is problematical, but one beneficial result is that the allied trades have certainly realized more thoroughly their unity of interests. This is shown by the much freer collaboration of the tanners, and by the encouragement now given to similar collaboration between their chemists. More evidence is found in the proposals for combined research.

There is also considerable reason to believe that there is some movement in the direction of partial State control. There is little doubt that evolution along trust lines will make this less difficult and possibly more desirable. The country cannot afford the spectacle of a Leather Trust permanently at war with a Labourers' Union. The public has realized that the well-being of the leather industry is vital to the national safety. It has realized that the leather trades are great producers of national wealth, and that increased production with the development of the export trade will materially a.s.sist to restore the country's financial position. It has realized also its own right to protection from bad leather and from exorbitant prices. On all these grounds it is probable, though there may be some reaction from the present position, that the State, which has already got its fingers in the pie, will refuse to draw them out altogether. The Imperial aspect of the question affords some further justification for this att.i.tude. The leather trades operate very largely upon imported material, and it is clearly desirable that there should be close co-operation between the home industry and the colonial supplies of material. Here too the war has also given a great stimulus in this direction. Indian myrabolans has long been a staple tanning material. South African wattle bark has during the last few years replaced almost completely, and probably to a large extent permanently, Turkish valonia. There has also been great increase in the imports of Indian kips and of South African hides, and it is not at all an impossible proposition to maintain a self-contained Imperial Leather Trade, should this be necessary. French chestnut extract, and quebracho extract, however, are much too valuable tanning materials to exclude for merely sentimental reasons. These instances indicate possible advantages in Imperial co-operation, but also show the need for caution in the elaboration of such schemes.

Although a partial, and indeed increasing, measure of State Control is probable, there has been as yet no serious proposal to nationalize the leather industry. Such a proposition, indeed, is hardly ripe even for discussion. Until the nationalization of transport and of mines is a proved success, and until the merely distributive undertakings of the munic.i.p.alities (_e.g._ of coal and of milk and other foods) are past the experimental stage, any proposition to nationalize the leather trades seems premature. It is noteworthy, however, that in Queensland, Australia, the Government have the right to commence and to administer State Tanneries.

Any progress in the direction either of democratization or of nationalization, has been certainly postponed by the sudden and unprecedented trade slump which commenced in the earlier part of 1920.

This depression, in spite of heavy falls in the prices of raw materials, has made economic production a much more difficult problem. It has undoubtedly given a further stimulus to evolution towards the trust type, and created a further tendency towards the closing of the smaller factories, and the employment of labour-saving devices. When the general fall in prices has made an appreciable fall in the cost of living, some reduction in the leather workers' wages, together with more efficient work, will also contribute to the solution of the difficulty. It is chiefly to be desired, however, that the export trade should be restored. The realization of this hope depends largely upon the establishment of peace and prosperity abroad, and the consequent stabilization of the various foreign exchanges.

PART V.--GELATINE AND GLUE.

SECTION I.--PROPERTIES OF GELATINE AND GLUE

Many of the chemical properties of gelatine, especially those which distinguish it from other proteins, have been described in the Introduction to this volume, and need no further comment. In this section its colloid nature and behaviour will chiefly be considered, for these points have greatest importance from the standpoint of industrial chemistry.

It is hoped, moreover, that this section will be of interest not only to the chemist concerned in the manufacture of gelatine and glue, but that it will be of value also to those concerned in leather manufacture. The difference between the "collagen" which composes the hide fibre and the high-grade gelatines is so small that for many practical purposes it may be considered negligible. Thus the description of the behaviour of a gelatine gel is very largely applicable to a hide gel also.

Gelatine has been crystallized by von Weimarn by evaporating a dilute solution in aqueous alcohol whilst in a desiccator containing pota.s.sium carbonate, the temperature being maintained at 60-70 C. The carbonate takes up water only, and the concentration of the alcohol therefore slowly increases until the gelatine is no longer soluble. Gelatine is usually found and known in the colloid state, however, and its behaviour in this state only is of practical importance.

The fundamental idea of modern colloid chemistry is that colloids are heterogeneous systems, usually two-phased, in which one phase is liquid and the other phase either liquid or solid. The latter phase, which is divided into small separate volumes, is known as the "disperse phase,"

whilst the other is the "continuous phase" or "dispersion medium." The "dispersity" is the degree to which the reduction of the dimensions of the disperse phase has been carried, and is best expressed numerically in terms of "specific surface," _i.e._ surface area divided by volume, but it is also often expressed as the thickness or diameter of a film or particle. When the dispersity is not high, we have ordinary "suspensions" and "emulsions," which with increasing dispersity merge into the typical colloids. By a.n.a.logy, colloids have been divided into "suspensoids" and "emulsoids," when the disperse phase is solid and liquid respectively. The cla.s.sification, however, has not been found satisfactory, for some systems in which the disperse phase is undoubtedly liquid, exhibit characteristic properties of suspensoids, and _vice versa_. A more satisfactory division, therefore, is found in the presence or absence of affinity between the two phases, the systems being termed "lyophile" and "lyophobe" respectively. If water be the continuous phase the terms "hydrophile" and "hydrophobe" are often used.

Broadly speaking, the lyophile colloids correspond to the emulsoids, and the lyophobe colloids to the suspensoids. Gelatine is a typical hydrophile colloid.

Another fundamental idea of colloid chemistry is that the great extension of surface involved in a high dispersity causes the surface energy to be no longer a negligible fraction of the total energy of the system, and that the recent advances in knowledge respecting surface phenomena may be called in to a.s.sist in the explanation of the special properties of the colloid state. Particles which exhibit the Brownian movement, about 10^(-5) cm. diameter, down to the limit of microscopic visibility (10^(-3) cm.) are termed _microns_. Particles less than this, but just visible in the ultra-microscope (510^(-7) cm.) are termed _submicrons_. Particles still less, approximately 10^(-7) cm., have been shown to exist, and are termed _amicrons_. The dimensions of molecules such as may exist in true solutions are of the order of 10^(-8) cm. A colloid sol may contain particles of various sizes. Thus a gelatine sol (like other lyophile systems) contains chiefly amicrons, but submicrons are also observable.