Page:Popular Science Monthly Volume 41.djvu/362

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348
THE POPULAR SCIENCE MONTHLY.

stated that these laws were passed in consideration "of the damage or injury which many sustained by the ill-curing of leather, and by the shoemakers in making it up into shoes and boots." Thus left to shift for itself, the industry steadily though slowly progressed with the country until 1860, when new inventions and improvements in processes, and energetic men at the head of it, gave it a decided impetus which has constantly gained in force since.

As has been said, the fundamental processes of tanning have changed very little since the early days. The hides, as they came

PSM V41 D362 Union splitting machine.jpg
Fig. 8.—Union Splitting Machine.

to the tanner, were first washed, and then, in order to remove the hair, soaked in vats of water and lime or ashes. After having been thus unhaired, they were put over a beam and scraped until every remnant of flesh had been removed. After another washing they were "laid away"—that is, packed in vats in alternate layers of ground hemlock or oak bark. The object of this was to bring about the desired union of the gelatin and tannin. The operation, however, was a slow one, and oftentimes many months were required to complete it. But study, of course, has been since given to the details of these various steps, which has resulted in a marked saving of time. In the preliminary process of depilation there are two methods which are now commonly followed by American tanners. The first is known as the "liming," which is used largely in the preparation of upper leather; and the second, known as "sweating," which is used for sole leather. In the "liming" process the hides are soaked in a solution of lime and water, as indicated above, until the hair-bulbs are loosened. In sweating there are two methods also: the warm sweat, with the temperature of the pit at 100°; and the cold sweat, with it at 50° or 60°. The former method is in general use in southern Europe, while the latter is not only American in origin, but is the