INDIAN YELLOW.

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decolourised by exposure to light, and also by the adtion of heat. Sulphuricacid dissolves carotin, forming a violet solution ; sulphurous acid colourscarotin indigo-blue. Formula, C^H^O.

Purrhee, or Indian Yellow.

Purrhee has been of late years imported into Europe, chiefly from India andChina. It appears to be of animal origin, and to consist of intestinal concre-tions or urinary calculi, or deposits from the camel, elephant, and buffalo.

Purrhee is partly soluble in water, and is, on nearer investigation, found tobe the magnesia-salt of a yellow-coloured sparingly soluble acid, namedeuxanthic acid, which may be prepared by first washing the dye-stuff with hotwater; the residue (euxanthate of magnesia) is dissolved in dilute boilinghydrochloric acid, from which, on cooling, the euxanthic acid crystallises inneedle-shaped crystals ; sparingly soluble in cold, more readily in hot, water,also in hot alcohol, from which the acid is deposited again on cooling.

The formula of this acid is C^H^Ou. By dry distillation, and also by theadtion of strong sulphuric acid, it is converted into euxanthon, C 20 H IZ 06, ayellow substance, sublimable in needle-shaped crystals; sparingly soluble incold water and alcohol, but more so in the latter liquid when boiling.

Cotton, previously mordanted with alumina, is dyed yellow in a bath madeup with purrhee water and borax or sal-ammoniac ; silk is dyed yellow whenimmersed into a solution of purrhee in borax, the colour obtained beingsulphur.yellow. Euxanthate of magnesia (i. e., the main constituent of purrhee)may also be decomposed by nitric acid not used in excess, and the aqueoussolution of that fluid may be applied in the dye-beck without the addition ofother substances: the colour thus obtained is apricot-yellow.

Yellow Colouring Matters of the Lichens.

Chrysophanic, Vulpic (Chrysopicric), and Usnic Acids.—We have al-ready seen that some kinds of lichens contain colourless acids, capable ofyielding, under the joint influences of ammonia and air, coloured substances.Other kinds of lichen contain ready-formed yellow dyes. Herberger, Rochleder,and Heldt, have extradted from the wall lichen ( Parmelia parietina) a yellowacid (chrysophanic), largely found in the rhubarb root {Rheum palmatum), andin the Rumex patientiiz and Rumex obtusifolius ; and Dr. Stein has obtainedfrom the lichen just named a yellow principle (chrysopicrin) identical withvulpic acid, obtained by Mueller and Strecker from a variety of Norwegianlichens ( Citraria vulpina, Evernia vtdpina), and by MM. Bolley and Kinkelyn,the Evernia vtdpina from the Alps. Usnic acid—found by MM. Knop, Roch-leder, and Heldt, in the Usnea fiorida , Usnea hirta, Usnea plicata, Usneaharhata, Cladonia rangiferina , Parmelia purpuracea, and Ramolina calicaris—completes the list of the yellow substances produced by lichens, all of whichhave great similarity with each other. The yellow-coloured matter found byM. Picard* in the leaf-buds of the poplar tree ( Populus nigra, Populus pyrami-dalis), and named chrysinic acid, approaches vulpic acid.

Since the yellow-coloured acids of the lichens are scarcely soluble in water,but readily soluble in alcohol, ether, and alkaline solutions, from which theseacids may be obtained in a crystalline state, the process of extradtion from the

* “ Journal fur Praktische Chemie,” xciii., 369.