CHROME-TANNING. The possibility of tanning by the use of chromium compounds, instead of the older tanning materials, was discovered as early as 185t by a German chemist, but the first process which attained commercial success was invented in 1884 by Augustus Schultz. The introduction of this process in Philadelphia caused it to become at once a great leather manufacturing centre. Chrome-tanning consumes only a few hours, as compared with weeks or months required by the older method, and it pro duces a leather which is extremely soft and pli able, of close texture, and thoroughly resistant to water. At the close of the nineteenth cen tury two-thirds of the glazed kids made in the United States were chrome-tanned, but the proc ess had not been applied successfully to sole leather. The process consists in treating the skins at first with a weak solution of hichromate of potash, to which sufficient hydrochloric acid is added to liberate the chromic acid. Of course
pickled skins may be used without the necessity of adding free acid. After the skins have taken up a bright yellow color, through their entire texture, they are drained and transferred to a bath of hyposulphite of soda, to which some acid is added to liberate sulphurous acid, which re duces the chromic acid to green chromic oxide. The sulphurous acid is at the same time oxi dized to sulphuric acid, until the whole of the chromic acid is reduced. The leather so produced is of a pale bluish-green color. The combination of the hide fibre, or corium, with the chromium oxide is apparently more stable than its combina tion with tannin, and yields less to boiling water. The leather can also be dyed successfully if the dye is applied while the skin is still wet, but so great is its water-repellent character that, once dried, it cannot be wetted sufficiently to dye properly.