Page:Popular Science Monthly Volume 41.djvu/363

 favorite one with tanners on this side of the water. Again, the process of depilation is still further hastened by the use of a mineral acid, like sulphuric, or by the handling of the hides in the old sour liquors where the tannic acid has become largely converted into gallic acid. There are strong advocates of both cold sweating and warm sweating, and of acid and non-acid methods, but there are no data on which pre-eminence can be assigned to any one of them. All have played an important part in abbreviating the tanner's work. Following depilation the hides are colored or passed through a series of vats containing liquors of varying strengths, and then laid away. Here, also, it is a matter of opinion as to what is the proper time that should be given to each of these operations. The late Hon. Gideon Lee, in a course of lectures on the art of tanning, declared, that he found quick-tanned leather of firmer and closer texture, and at the same time heavier and more durable. By keeping the hides too long in the liquors or vats the gelatin was disolveddissolved [sic]. But, whatever the general census of opinion, these processes have reduced the time required in the tanning of a hide from twelve and eighteen months to four and six months. Visions of a still greater abbreviation have been common, and "quick tanning processes" appear about so often. Some of these are historical. They include attempts to force the tannin into the hide by



hydrostatic pressure, and by the pressure of the air under an exhausted receiver. They include the application of the principles of osmose and kyanizing. The latter experiment was made by a young English engineer, who in his early life had been engaged in preserving wood by kyanizing with chemical agents. He came to this country and spent ten thousand dollars in constructing a large iron, egg-shaped, copper-lined tank. This was capable of holding one hundred butts, and of resisting an immense pressure. He provided pumps so that he could exhaust the air of this tank,