The Puering, Bating & Drenching of Skins

by Joseph Turney Wood

2. The bate described and set forth in the accompanying specification.

Wood’s American Patent (638,828, Dec. 12, 1899) Bate.—This invention has reference to improvements in and relating to the means, liquid, or bate, used for the bating or puering of skins previous to the process of tanning the same.

At the present time, skins are usually bated by means of a liquid or bate prepared from dog or pigeon dung; and, although the bating action or actions have not hitherto been thoroughly understood, it is a well-known fact that fermentations which the dung undergoes play an essential part. It was also pointed out, by H. E. Procter in 1885, in his “Text Book of Tanning,” that the action of the bate was in a great measure due to bacteria. It is also a known fact to practical tanners that a dung bate properly applied produces the finest and most supple leather. Owing, however, to the varying compositions of the dung used, the bate made therefrom possesses varying properties: its bating action is uncertain, its properties are readily affected by atmospheric influences, and the skins treated are liable to putrefaction.

As a substitute for a dung bate, it has been proposed, as set forth in the specification of the British Patent No. 21,720, A.D. 1895, and the specification of the German Patent No. 86,335, Class 28, to use a bate made from a pure culture of bacteria. Such bate, however, does not possess all the essential properties of a dung bate, and, although bacterial action is necessary, such action alone is not sufficient, as was pointed out by me in 1894 in the “Journal of the Society of Chemical Industry.”

I have now discovered that the bating action of a dung bate is due to the combined action of enzymes, or unorganized ferments, and certain chemical compounds, which compounds consist principally of amines—i.e. ammonia in which one or more atoms of hydrogen has or have been replaced by alcohol radicles—in combination with organic acids usually found in dung, and of the compounds so formed the lactates and acetates are the most important. I have also discovered that the bating action of the enzymes alone, or the action of the above-referred-to chemical compounds alone, is inefficient, and that the enzymes exert their bating action in the presence of the chemical compounds, while these latter, in addition, have an independent action on the limes in the skins, and on the skin fibre.

The object of this invention is the production, according to scientific methods, of a bate having similar properties to those of a dung bate, such properties in the improved bate being modified according to the requirements of the skins to be bated and the leather to be produced.

According to this invention, the liquid or bate is made by producing by fermentation, an enzyme or enzymes of the same character as the enzymes contained in dog dung, or produced from bacteria contained in the dung, and to the liquid thus obtained there is added an organic acid and an alkali.

I have discovered that for an efficient bate a pure culture or single species of bacteria is insufficient, and that no single organism hitherto isolated will give results equal to dung. I have also discovered that the production of enzymes of the character above referred to, depends more upon the composition of the nutrient medium in which the bacteria are cultivated, than upon the kind of bacteria, although these latter must be capable of producing the required enzymes, the production of which appears to be due to a symbiotic growth of bacteria at present little understood. The bacteria used for the purpose of this invention may be the bacteria found in dog dung, or the bacteria obtained from the roots of the hairs of skins during the sweating process, these latter being used, by preference, on account of the ease with which they are obtained, compared with the difficulty of isolating from the dog dung the particular mixture of species most desirable, there being so many undesirable species present. Of the bacteria found on the roots of the hair during the sweating process, and hereinafter referred to as “sweating” bacteria, I have found that two species predominate, and, so far as I am aware, these have not been previously isolated. The principal organism, which I call “bacillus d,” in continuation of a series of previous investigations described in the “Journal of the Society of Chemical Industry,” A.D. 1898, forms large whitish colonies, with irregular contour spreading on the surface of the gelatin, the bacilli being very small, mostly occurring in pairs, but sometimes joined together in thread-like forms. The second organism, called by me “bacillus e,” forms small brownish-yellow boat-shaped colonies on gelatin plates. The bacteria consist of plump cells two or three times the size of bacillus d, united in pairs and chains, but the cells vary considerably in size, and are surrounded by a capsule. I have discovered that the above bacteria, when used separately as pure cultures, exert little or no action on the skin, but when used together the action is very remarkable.

The gelatin and gelatin plates referred to in the above description are the gelatin and gelatin plates used for the cultivation of bacteria, according to the ordinary bacteriological methods as described in Günther’s “Bakteriologie,” published by George Thieme, Leipzig, in 1898, and in other text-books.

In the accompanying drawings, made from photographs which are of record in this case, the bacillus d is shown in Fig. [21], and the bacillus e in Fig. [22], both photographs showing the bacilli magnified 1000 diameters.