INDIGO′TIN

Syn. Cerulin , Indigo blue . This is the pure blue principle of indigo. It appears to be the oxide of the same organic radical of which indigo white is probably the hydrate. Prep. 1. Indigo (in fine powder) is digested succe ively in dilute hydrochloric acid, solution of pota a, and alcohol; the dried residuum is crude indigotin. 2. Indigo (in fine powder), 1 part; green sulphate of iron, 2 parts; hydrate of lime, 3 parts; water, 15 parts; mix, agitate occasionally until the colour is destroyed, then decant the clear portion, precipitate with dilute hydrochloric acid, and wash the powder first with water, and then with boiling alcohol, until the latter ceases to acquire a yellow colour. 3. Caustic soda and grape sugar, of each 1 part; water, 20 parts; powdered indigo, 5 parts; mix, and proceed as last. The above are e entially the same as the indigo vat, but on the small scale. 4. The proce for estimating the value of indigo given under Indigo is a good proce for obtaining Indigotin. Obs. The product from all the above exceeds 50% of the indigo operated on. 5. (Taylor.) Powdered indigo, 2 parts; plaster of Paris, 1 part; water, q. s. to reduce the mixture to a thin paste; spread the ma evenly upon an oblong iron plate to the depth of about 1 ⁄ 8 inch, and dry it by a gentle heat. It must then be held over the flame of a spirit lamp, when a disgusting odour will be evolved, the ma will begin to smoke, and in a few minutes will be covered with a heavy purple vapour, which will condense into brilliant flattened prisms or plates of an intense copper colour, forming a thick velvety coating over the surface immediately exposed to the heat. Should the ma catch fire, it may be instantly extinguished by a drop of water let fall upon it. Prod. 15 to 18%. See Indigo , .