Red dyes must neither color soap-and water nor lime-water, nor must they themselves become yellow or brown after boiling. This test shows the presence or absence of Brazil-wood, archil, safflower, sandal-wood, and the aniline colors. Yellow dyes must stand being boiled with alcohol, water, and lime-water. The most stable yellow is madder- yellow; the least stable are anatto and turmeric; fustic is rather better. Blue dyes must not color alcohol reddish, nor must they decompose On boiling with hydrochloric acid. The best purple colore are composed of indigo and cochineal, or purpurine The former test applies also to them. Orange dyes must color neither water nor alcohol on boiling; green, neither alcohol nor hydrochloric acid. Brown dyes must not lose their color on standing with alcohol, . or on boiling with water.

If black colors nave a basis of Indigo, they turn greenish or blue on boiling withsodium carbonate; if the dye be pure gall-nuts, it turns brown. If the material changes to red on boiling with hydrochloric acid, the coloring matter is logwood without a basis of indigo, and is not durable. If it changes to blue, indigo is present.