The Puering, Bating & Drenching of Skins

by Joseph Turney Wood

The advantage of this invention also consists in its being possible to make better bates than that which is made, for instance, from dogs’ dung because, as hereinbefore stated, it is a disadvantage of this latter bate that it in many cases dissolves too large a quantity of the albuminous substance. Otherwise, the composition of the improved bate quite coincides qualitatively with the composition of dogs’ dung, as the latter actually consists in addition to the unabsorbed portions of food, of secretions of gall, the pancreatic gland and the mucous membrane of the intestines. The trypsin and steapsin respectively as well as being derived from the pancreatic juice, may also be derived from the vegetable kingdom, for instance, there are considerable quantities of trypsin in the sap of the fig. Steapsin, in not inconsiderable quantity, is found in the saps of flax, hemp, maize, etc.

It must also be remarked that the colouring matters in gall are of quite subordinate importance, and may be disregarded. The view formerly adopted that the colouring matters in gall stain the leather is incorrect.

Example:—200 c.cm. of gall juice in 1 litre of water are mixed with the watery extract of 200 grm. of chopped small intestine in 1 litre of water on the one hand, and 100 grm. of the pancreatic gland in 1 litre of water, on the other hand. This watery solution is added to the bating bath, according to the bating action desired. It can also, in order to allow of being more easily handled, be obtained in solid form by absorption in sawdust or kieselguhr and drying at 30° to 40° C.

Claim.—A process for bating hides, characterised by the use of mixtures of gall, the secretion of the pancreatic gland and intestinal juice, and by the use of mixtures of the active enzymes in these, or active enzymes derived from the vegetable kingdom, substantially as described.

Prof. Dr. H. Becker’s English Patent (24,982, 1910).—Improvements in Puering and Bating Hides and Skins.—It has been shown by Wood, of Nottingham, and by Dr. Popp and Dr. Becker, of Frankfort-on-the-Main, that the action of a good puer or bate on hides, is connected with the development of certain species of bacteria.

The preparation of pure cultures of these bacteria (which are derived from dog dung) has enabled what may be properly termed a safe puer to be obtained, inasmuch as by its use overpuering the hides is entirely prevented. Furthermore, the leathers are fuller and do not lose any excess of hide substance, so that a dozen sheepskins that have been suitably puered by the bacteriological method, will weigh about 9 ounces more than a dozen skins of the same kind and origin, that have been treated in exactly the same way in other respects, but puered with dog dung.

The method of action of the bacterial puer has been elucidated as follows. The bacteria present in the puer are microscopically small and pass easily into the skin through the pores of the latter, while on the surface and in the substance of the skin they produce their metabolic products and enzymes. These substances are partly proteolytic, partly fat decomposing, and also diastatic in character, so that the highly proteid intermediate substance of the skin is degraded. By means of the ultimately formed ammonia, amine bases and ammonium bases assisted by the action of organic acids produced by the bacteria, the lime soaps are decomposed. Lime and fat are partially dissolved, and partially further decomposed or converted into a form which enables them to be worked out by mechanical means. At the same time the roots of the hairs are also loosened so that the hairs also can be readily removed by mechanical treatment.

Another essential factor is the liberation of gases formed within the skin by the action of the micro-organisms and exerting a very gentle pressure on their environment. The structure of the fibres is loosened, the fibrils are straightened individually without sustaining any important loss of corporeal matter, and in this way a firm, tough and yet soft handling leather is obtained. Attempts have been made to improve this puer by adding, for instance, organic acids and salts to the bacterial cultures.

Other methods of puering, based on the direct weakening of the skin fibres from the outside, may also effect the pulling down of the hides, and moreover, in consequence of that attack on the skin fibres without straightening the fibrils, an immoderate amount of substance is lost, and therefore a hard, stiff, thin and light leather is obtained.