The Boot and Shoe Manufacturers' Assistant and Guide. / Containing a Brief History of the Trade. History of India-rubber and Gutta-percha, and Their Application to the Manufacture of Boots and Shoes. Full Instructions in the Art, With Diagrams and Scales, Etc., Etc. Vulcanization and Sulphurization, English and American Patents. With an Elaborate Treatise on Tanning.

by Unknown

It is to this latter—the materials for tanning—that I wish more particularly to call your attention.

We greatly need both a qualitative and quantitative analysis of the several kinds of substances used for tanning, especially of the hemlock bark—of the white, black, red, Spanish, chestnut, oak, and other varieties of the Quercus; also of the American and Sicily sumacs, and of catechu or terra japonica. We have many native trees and shrubs, of whose barks an analysis might prove to be something more than mere scientific curiosities.

A writer in one of our scientific journals asserts that the bark of the chestnut contains more tannin than oak, and more coloring matter than logwood of equal weights and qualities. On what authority he makes this statement, I know not, but if the fact be so, it should be established and known.

I am not ignorant that Sir Humphrey Davy and other distinguished foreign chemists have investigated this subject to considerable extent, but the barks and substances examined by them were not our indigenous products; besides, since their day, better and more accurate methods of analysis have been discovered, so that even their experiments need revision, and many of their conclusions may need correction.

According to Sir H. Davy, terra japonica contains about 54 per cent. of tannin, and is equal in tannin properties, to 6 or 7 lbs. of English oak bark, and to three lbs. of Sicily sumac. The tanners of this country consider American sumac as possessing only half the amount of tannin of the foreign and imported article; and it is worth only half as much per ton: hence it would require 6 lbs. of it to equal 1 lb. of terra japonica or catechu, and is, therefore, equal in tanning to English oak bark. But the hemlock of this country has probably double the amount of tannin that the white oak of the Northern States has; hence it holds a middle rank between Sicily sumac and terra japonica, and would consequently require 4 or 5 lbs. of it to equal one of the latter.

But the quality of the tannin, or rather the quality of the leather produced by these different kinds of tanning materials, is a matter of quite as much importance as the relative or absolute quantity of tanning contained in each of them. While terra japonica possesses the greatest quantity of tannin, it is considered as producing the most inferior quality of leather. So hemlock, which, excepting the Sicily sumac, possesses the next highest quantity, produce the next worst quality of leather; while the oaks, which are the lowest in the scale of quantity, afford the most superior in quality. And although the American and Sicily sumacs may be considered to be on a par with the oaks, as to quality, yet the same law seems to hold with respect to each other; that is, the American sumac, which possesses only about half the amount of tannin, makes a better quality of leather than the Sicily sumac.

Now pure tannin is probably the same in all cases, then why this great diversity of quality in the leather? A careful chemical analysis of the substances used, would determine the question; but, in the absence of such analysis, we readily and perhaps correctly conjecture, that very different vegetable gums, resins, acids, extracts, &c., must be combined with the tannin in these several tanning materials, which being also soluble in water, combine in some way with the gelatine of the hide as well as the tannin, and become fixed, although none of them could alone be made to unite thus permanently with the hide. It becomes, therefore, a matter of much importance to the tanner to know what these several vegetable products are which are combined with the tannin of each species of bark, or substance used for tanning, and as they are not merely useless, but injurious, to know how, if possible, he may get rid of them. Among these products, there is in hemlock bark a large amount of resin or pitch, a small portion of which, however, is soluble, unless very hot water is used in leeching the bark; but in all barks there is, besides extractive or coloring matter, a large amount of acetite of potash, which is nearly as soluble as tannin itself, and which is always leeched out of the bark and forms a part of the tan liquor or ooze in which the tanner steeps his hides. That the potash, which abounds in all barks, is leeched out, is evident from the fact, that ashes, obtained from burning the leeched bark of tan yards, will not afford a ley sufficiently strong to make soap. The same thing is true of wood that has been long soaked in water. The black oak or Quercitron—the Quercus Tinetosia which is so valuable for its coloring properties, is among the richest of barks in tannin, and makes the best quality of leather, but it is generally abhorred by tanners, and avoided in the first stages of tanning. It abounds in a rich, deep yellow precipitate, which attaches itself, like paint, so tenaciously to the surface of the hides, that the tannin penetrates very slowly. But by the Hibbard process of tanning, the hydrochloric acid used decomposes and neutralizes both the potash and coloring matters leeched out of the bark, in a great degree, so that the process of tanning is more rapid, and the color of the leather much fairer and more beautiful, besides it, the leather, being tougher and more pliable.

Here then, in the analysis of our indigenous barks, is a field large enough to give useful and honorable employment to all the first chemists of the country. Not possessing, myself, either the time, skill, or requisite means to pursue this subject, but believing that you possessed them all, in addition to a taste and zeal for such pursuits, I have taken the liberty to present those views and suggestions for your consideration.

There are other matters connected with this subject which belong rather to the commercial and agricultural business of the country, but are not wholly devoid of interest to the naturalist and chemist. I allude to the quality and quantity of tanning materials as produced and influenced by latitude, locality, and climate. In the Eastern, Northern, and Western States the quality and quantity of tan barks are far inferior to those of the Middle, Southern, and South-western. The facilities and natural resources of the South for manufacturing leather, over those of the North, as far exceeds those of the latter, as the actual amount of leather and shoes manufactured by the North exceeds those manufactured by the South.

The South, in fact, ought to furnish the North with leather; and should, moreover, produce all the sumac needed for home consumption, both for dyeing and tanning, of which we now import large quantities. By procuring from the coast of the Mediterranean the best varieties of sumac, viz., the Rhus Coriana and the Rus Cotinus—the former used chiefly in tanning, and the latter in dyeing, the South might grow enough in a few years for export, and find it a profitable branch of industry.