[ TANNING. ]
The following is the French mode of tanning all kinds of leather in a short time, highly important to the manufacturers of leather in this country, as it points out a secure and profitable mode of turning their capital twelve or thirteen times in a year, instead of once.
Washing Hides.
The best method of washing hides is to stretch them in a frame, and place them, thus stretched, in running water. If running water cannot be conveniently had, still water can be made to answer by frequent stirrings and agitations; the remainder of the operation of cleansing is performed as in the common way.
On taking off the Hair.
Begin by shaking some lime in a pit, to which put a great quantity of water, then stir this water well, that it may become saturated with the lime, then place your hides in the pit perpendicularly; for this purpose, several wooden poles should be fixed across the pit; to these poles the hides are to be fastened with strings at proper distances, each hide being first cut in two; whilst the hides were thus placed in the lime water, the lime itself, which had deposited on the bottom of the pit, was frequently stirred up to increase the strength of the water, and to make it more operative; the hair thus treated, will, in about eight days, come off the hide with great ease. A shorter and a better method may effect this purpose in two days; that is, to plunge the hides, after being washed and cleaned, into a solution of tan, which (having been already used) contains no longer any of the tanning principle, mixed with a five hundredth, or even a thousandth part of the oil of vitriol, commonly called sulphuric acid; this operation not only takes off the hair, but raises and swells the hide; as, in the old way, is generally effected by barley sourings. However, further swelling and raising is necessary, and the hides should again be plunged in another quantity of spent tan-water mixed with the one thousandth part of the oil of vitriol, and thus steeped a second time; their swelling and raising will be completed in about forty-eight hours; after this operation the hides will acquire a yellow colour, even to the interior part of their substance. To determine if the swelling and raising be sufficiently completed, let one of the corners of the hide be cut, and if it is in a proper state there will not appear any white streak in the middle, but the hide throughout its whole substance will have acquired a yellow colour, and semi-transparent appearance. Mr. S—— is of opinion, that swelling and raising hides is not necessary, and that the hides tanned without this operation are less permeable to water. On tanning on the new principle, as practised by Mr. S——, he places several rows of casks on stillings sufficiently elevated above the ground to place a can or tub under them; these casks were filled with fresh finely ground tan, then a certain quantity of water was poured into the first of them, which water, as it ran through the tan, exhausted and carried off the soluble part, and as fast as it ran into the vessels below, was taken away and poured on the second cask, and so on successively until the solution was sufficiently saturated, and thus it may have been brought to ten or twelve degrees of the arometer for salts. In order to exhaust the tan of the first cask, Mr. S—— continued pouring water on the first cask until it ran off clear; at which time the tan was deprived of its soluble part; these liquors, as it may be easily conceived, were carefully kept for future operations; large wooden vats are considered the best sort of vessels for holding this solution, as well as for making and preparing it; hogsheads, on a small scale, may be made to answer. It is particularly in the use of this solution that Mr. S——'s method consists; the quickness with which the solution acts is truly astonishing, and when we see it, there is cause of surprise in thinking why it was not found out before. As soon as the hides are taken out of the water, impregnated with sulphuric acid, Mr. S—— puts them into a weak solution of tan, in which he leaves them for the space of one or two hours; he afterwards plunges them into other solutions of tan, more or less charged with the tanning principle, in proportion to their strength, so that in the experiments at which we were present, some heavy hides were tanned in six or eight days, others in twenty and twenty-five days. In placing the hides in the solutions, some precautions are necessary; the hides should be suspended on a wheel, or in a frame where they should be stretched, and placed one inch apart, so as to admit the solution freely about them; Mr. S—— recommends cutting off the head and the neck of the hide, and a slip down each side, in which slip the feet and belly part are to be comprehended; and the circumstance which determines Mr. S—— to cut the hide in this manner is, that the feet, and the parts that are near the belly, are more spongy and more easily penetrated by the tan; and as they produce leather of an inferior quality they may be more advantageously tanned separately, than put promiscuously into the solutions of tan with the rest. The remaining part of the hide is to be divided into two or more parts or pieces, so as to be easily placed in the vats or casks.