2.—Yellow and Orange Dyes.
Heat some of the paper with a not too dilute solution of tin salt in hydrochloric acid. If the colour is unchanged, with a colourless or yellow solution, boil some more paper with milk of lime. A change to reddish or brown shows turmeric or a congener. Absence of change shows phosphine, quinoline yellow, or a natural dye-stuff. If the acid tin solution turns the paper red, and then quickly bleaches it to a pale yellow, we have fast yellow, orange IV., metanil yellow, brilliant yellow, or the like. If the tin turns the paper greyish, heat another portion with ammonium sulphide. A blackening shows a lead or iron yellow. If there is no change, we have naphthol yellow, auramine, azoflavine, orange II., chrysoidine, or one of their allies.