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Aniline Black on Wool
For 2 pounds of wool a bath is prepared of 20 quarts water, 3 ounces permanganate of potassa, 41 ounces sulphate of magnesia.
The use of sulphate of magnesia has for its object, to prevent the formation of caustic alkali, and has already been proposed by Tessié du Mothay. The wool is impregnated with this solution. and left in it until the fluid has become colorless, or nearly so, whereby it is colored dark-brown and covered with brown oxide of manganese. This process takes place easily in the cold, but it is best to dissolve the permanganate in hot water. The wool is now pressed out, and, without washing, conveyed into a bath of 12 ounces commercial aniline oil, 21 ounces commercial hydrochloric acid, and 8 quarts water, where it is moved about in the cold it attains here directly a dark green-black color. It is pressed out again, washed in water containing a little soda, and treated with a weak solution of 1/80 ounce bichromate of potassa in 10 quarts water. The color becomes now dark black, when the wool is washed with water and dried.