Dr. Gale—Dear Sir: As a chemist interested in the discovery of new chemical facts, and as an American citizen in the development of all branches of industry of our common country, permit me to call your attention to the following remarks and suggestions.
For two years and a half past I have been engaged, more or less of the time, in the investigation and development of an improved system of tanning, founded, as I flatter myself, upon a more correct knowledge of the chemical affinities and qualities of the various substances used, and of the processes employed in making leather.
The art of making leather embraces two species of operation, viz., the chemical and mechanical: the first includes all the changes produced in the raw hide, by means of other substances applied to it, till it becomes leather. The second, all the physical labor expended upon it, whether by manual tools or machinery. The first is by far the most essential and important, and yet it is that which is least understood by practical tanners. For the want of chemical knowledge they are, in a great degree, incapable of understanding and appreciating the chemical phenomena daily passing before their eyes; hence improvement in the art of leather-making has been very slow: and those improvements which have been attempted belong chiefly to the tools and machinery employed. Very few tanners have ever ventured upon an improvement in the chemical branch of their art; and when they have, their supposed inventions or discoveries were in direct contradiction of chemical laws, and of course were impracticable and soon abandoned: as, for instance, patents have been taken out for the use of potash and soda ash, dissolved in the tan liquor or ooze. One man, a few years since, actually obtained a patent for the suspension of bags of ashes in the tan vats. If he were a tanner he must have known, what every practical tanner knows, that lime, remaining in the hide, prevents the process of tanning, besides making bad leather; but he did not know that lime and potash were both alkalies, and that tannin was an acid, and that alkalies and acids neutralize each other, and therefore for his purpose, incompatible, or he never would have made such an absurd mistake.
For the last fifty years, nearly all the improvements, real or supposed, that have been patented, were chiefly for tools or machinery, for the purpose of expediting the mechanical labor necessarily employed, but the discovery and improvements which I have been investigating appertain solely to the chemical processes of tanning. They were first proposed by Harmon Hibbard, to whom letters patent were granted, as you are already aware; and with which improvements, and the chemical principles on which they are founded, you are familiar, having given them a careful and patient examination pending his application for a patent. But it is not my purpose to discuss these topics now, and I will dismiss this part of my subject by a quotation from Dr. Ure, and by offering a remark or two thereon.
In his dictionary of the Arts, Dr. Ure says:—“Various menstrua have been proposed for the purpose of expediting and improving the process of tanning; among others, lime-water and a solution of pearlash; but these two substances form compounds with tannin, which are not decomposable by gelatine; it follows that their effects must be prejudicial. There is very little reason to suppose that any bodies will be found, which, at the same time that they increase the solubility of tannin in water, will not likewise diminish its attraction for skin.”
Now the very objects here supposed by Dr. Ure to be unattainable, are literally and perfectly accomplished by Hibbard’s method, viz., a menstrum has been found “for expediting and improving the process of tanning,” and that, too, by “increasing at the same time both the solubility of tannin and its attraction for gelatine or skin;” by means, also, so simple, direct and obvious, that it is wonderful that so learned a chemist as Dr. Ure should not himself have made the discovery.
But I come now to the principle object in view in this communication.
During the experiments and investigations above alluded to, my attention has been directed to two important branches of the manufacture of leather.
First. The chemical principles involved in the several processes of making the various kinds of leather, whether it be in “tawing,” as in making kid glove leather, or in oil dressing, as in making buckskin and chamois leather, or in tanning proper, as in making morocco, upper and sole leather.
Second. The various species and qualities of the tannin materials used, viz., the bark of hemlock, several varieties of oak, American and Sicily sumac, and terra japonica: these embrace the chief kinds used in this country.