The Foreign Supply of hides is also of great importance and value. In the case of imported hides precautions to prevent putrefaction are essential, and some method of "curing" is always used.
Salting the hides is one of the most satisfactory methods for temporary preservation. The action of salt is hygroscopic, and mildly antiseptic. Moisture is withdrawn from the hides, which are then under conditions no longer favouring the growth of bacteria. Well-salted hides will keep for years, especially if quite clean. A light salting is also useful for a short preservation, and is becoming common in hide markets and tanneries during the summer and autumn months. Salting is a method used extensively in the United States. The "packer hides" of the stockyards are carefully and systematically salted with about 25 per cent. of salt and stored in cool cellars. The hides are so piled up in heaps, that brine easily drains away. The great disadvantage of salting is the so-called "salt stains." These stains have been ascribed to the iron in the salt, to the iron in the blood, to calcium sulphate in the salt, and also to chromogenic bacteria, whose development is favoured by salting. The relative importance of these factors is not yet satisfactorily determined, but cleanliness and pure salt tend to eliminate the trouble.
Drying the hides is a less satisfactory cure. The principle is similar, viz. removal of moisture. Dried hides are, however, much drier than salted, and are quite hard and horny, hence the name "flint hides." The hides also lose much weight, a considerable advantage in reducing freight. Tropical hides are often flint-dry, and where preservatives are expensive or unprocurable, it is often the only practicable method of cure. Nevertheless, the method has many serious disadvantages, and is difficult to execute. If dried too slowly the hides putrefy partially; if too quickly they dry on the outside, and the interior is left to putrefy. The fact that hides are of uneven thickness, and the climate often hot, increases the difficulty, and often results in partial destruction of the fibrous structure of the hide. When dried, moreover, the hides are still subject to the attacks of insect larvæ, for the prevention of which the usual sprinkling of naphthalene or arsenic is only an imperfect remedy. This method of cure is also a nuisance to the tanner, who has to employ labour, pits and time in attempting to restore the hides to their original condition, and often loses up to ten per cent. of the goods in so doing. Dried hides are also subject to the presence of anthrax.
Dry Salting the hides is an excellent method of curing. As the name implies, it combines methods of drying and salting which are used alternatively. The method is used extensively in South America. A modified form of it is also used for preserving the "E.I. kips," which are cured, however, not with common salt, but with earth containing up to 70 per cent. of sodium sulphate. Dry-salted hides are largely free from the defects of dried hides, but of course are more trouble to the tanner in the process of soaking (see Section II., p. [16]) than the wet-salted goods.
Freezing the hides is now a commercial process. On the whole the process is satisfactory, but the expansion of water after freezing may tend to damage the hide fibres.
Sterilizing the hides has been frequently suggested, but no method has yet been advocated which does not interfere either with the tanning processes or with the quality of the finished leather.
Hides from the European Continent, usually wet salted and well flayed, exhibit much the same variable quality as the home supply, those from highland districts tending to be thick, yet even, well grown, tight textured and smooth grained, whilst those from lowland regions are less satisfactory. Thus hides from the Swiss Alps and Scandinavia have ranked high, whilst the spready Dutch cows are typical of a lowland hide. In the hides which once came from Germany the same features appear. Bavarian highland hides had an excellent reputation, whilst those from Berlin, Cologne, etc., tended to be long in shank and not well grown. French hides are often ill flayed, and Spanish and Portuguese are often subject to scratches. Italian hides have a very good name, being small but stout in butt.
The American supply is important. South America yields an excellent class of hide, salted or dry-salted. They are from an excellent breed of animals, slaughtered and flayed with every care, and efficiently cured. A most serious defect in this class of hide is the "brand," which is both deep and large and in the most valuable part of the hide. One side, however, is usually unbranded, so that each hide yields one good "bend." These hides, e.g. "Frigorifics," have recently been much more extensively tanned in Britain because of the shortage in the home supply of market hides caused by the European War. South America also yields good horse hides. North American hides are usually wet-salted (e.g. packer hides). They are usually good. Central America yields mostly dried hides exhibiting usual defects.
The Asiatic supply comprises the frozen China hides, which are clean but small, with flaying of uncertain quality. There are the buffalo hides from Asia and East Europe, which are suitable for cheap and sole and strap leather, and also the dry-salted "E.I. kips," obtained from a small breed of Indian cattle, and extensively made into upper leather. The Asiatic humped cattle also provide a limited supply. The African supply is of increasing importance. The tropical parts yield dried hides of uncertain quality, but the more temperate parts of South Africa yield a growing supply of good quality.
REFERENCES.
"The Manufacture of Leather" (Bennett), pp. 27-37.
"Principles of Leather Manufacture" (Procter), pp. 33-56.
"The Ox Warble or Bot Fly" (E. Ormerod).
"The Making of Leather" (Procter), pp. 2-22.