Natural tannin, comprising several species, originating from the different proportions of extractive and gallic acids. Also three kinds of artificial tannin, obtained by the action of nitric acid upon charcoal; also upon indigo and the various resins; also that obtained by the action of sulphuric acid upon the resins and camphor.
The best kinds of hides suitable for tanning into leather are those of heifers. The large ox hides are those which are used chiefly for conversion into sole leather. The skins of horses, cows, bulls, and buffaloes, are used for thick sole leather. For upper, thin, and the various fancy leathers, the skins of small animals, dogs, sheep, goats, seals, &c.
The quality of the leather depends upon several circumstances; the nature of the skin, its condition in curing, upon the method of tanning, also the nature of the food upon which the animal fed, and its healthiness. Hides from cattle slaughtered in cold weather are said to produce five per cent. more leather than when taken in the warm months. Dry hides produce more leather than salted hides. For the production of 40 pounds of leather, the average is estimated 30 pounds of dry hide—60 pounds of salted, or 74 pounds of market hide. Large supplies of skins are imported from Buenos Ayres, Brazil, California, and Texas. Sheep skins are received from the Cape of Good Hope and Buenos Ayres; goat skins from Barbary; lamb and kid from Italy. Very few hides, comparatively, are obtained at home. In order to form some idea of the extent of the leather trade, as represented in the tanning establishments, a few figures will enable the reader to judge.
There are, according to Morfit, 6,263 Tanneries in the United States, the largest number being in Pennsylvania. These unitedly employ 20,909 persons, and in which business is invested the sum of $18,900,557. The value of the products is $32,861,796. About 6,000,000 skins of sheep, goats and other small animals, are tanned and dressed annually, which are not included in the above estimate.
The Scientific American, in alluding to Morfit’s excellent work on the “Arts of Tanning,” had the following notice which we here insert:
“In looking over this book, and reading the different plans for improving leather, and for reducing the time occupied in tanning a skin or hide, we are more and more convinced of the important fact that the tanning art has been greatly improved by modern discoveries and application—a contrary opinion to that held by the universal mass of the people. We know it is very difficult to introduce new plans of tanning, for tanners are, like others, wedded to old things; thus the rolling of leather—an operation now generally practiced—was opposed with much bitterness by some of our most experienced tanners, one of whom said ‘he never would roll a hide while he lived,’ an assertion which he wisely lived either to forget or repudiate.
“The whole science of tanning depends on two principles, one the removal of the hair from the skin, with the least injury to the gelatinous matter of which it is composed, and the other is the rendering of the skin insoluble in water, and to resist the action of the atmosphere, and yet be flexible. The hair can be removed by lime, sweating, and other means, but the employment of a substance or substances that will combine with the gelatine of the skin to form a new substance, insoluble in water and incapable of being injuriously acted upon by the atmosphere, offers a wide field for the historian of the tanning art, and presents a subject for the study of every tanner at least in our country. The art of tanning was known, we suppose, before the flood; it is practised among all nations, civilized and savage, and the gist of it lies in soaking the skins in different solutions of various vegetable substances of an astringent character, until the tanning juices of those substances have combined with the whole skin and rendered it a new substance named leather. Oak and hemlock barks, sumac, willow, blackberries, catechu, kino, &c., are employed. Those who wish to get an account of the various processes and substances employed, must consult this book.
“We have only another remark to make, it is this, we have never known any of the metallic solutions to be employed in tanning, and from their nature, in rendering some vegetable substances insoluble, we believe that it would be worth the trouble for some of our tanners to make a few experiments. We would recommend the chloride of tin; it is made by feeding drop-tin into muriatic acid until effervescence ceases. The way to try it would be to make up a solution of it in a tub of cold water, until it stood about 1½° in the hydrometer; the skin should have undergone through the whole tanning process before it is placed in this solution, in which it should lie about two hours, and be stirred up two or three times. After this it should be well washed in cold water, and then finished in a milk-warm water bath, when it will be ready for drying. It is our opinion that a superior leather would be produced by this addition to any of the present processes.”
CHAPTER II.
TANNING AND THE TANNING WOODS OF AMERICA.
The following letter in 1851 was addressed by Dr. Reid, of Rochester, New York, to Dr. Gale, of the United States Patent office, respecting the art of Tanning, and the various substances which are, or may be used in the processes. It is a very able and elaborate document, and will be found to contain not only facts, but important suggestions which must be valuable to all interested in tanning.