A chrome tanning bath is made, according to an American patented process, in this manner. Twelve pounds of chromic acid are dissolved in 6 gal. of hydrochloric acid of a specific gravity of 1.146; 50 lb. of chrome alum are dissolved in about 20 gal. of water; thirdly, 73 1b. of washing soda are dissolved in about 10 gal. of water. The soda solution is now slowly poured into the chrome alum solution until the result appears cloudy and a sparkling silver mist is seen on the surface, when water is added to make up the liquid to 44 gal. The solution is now run into the chromic acid solution and the whole allowed to settle. A 1 1/2 per cent. solution of this liquid is used for the chrome bath {i.e. l 1/2 gal. of the liquid to 98 1/2 gal. of water) for tanning, and the hides are hung in this. As the tanning proceeds, the strength of the bath is made up by more liquor to 4 or 5 per cent., and the temperature of the bath is kept at 80°F. When the thickest parts of the skins show a bluish-green colour, the tanning has proceeded far enough •. the hides are then washed in water containing 1 oz. of borax in 20 gal.

The time of tanning is for sheepskins about one hour; goat-skins about one and a half hours; calf-skins two to four hours; and heavier materials ten hours.