PURPURIN.

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and a perfectly definite elementary composition. The separation of thesesubstances is based upon their varying solubility in alcohol and benzol. Theyellow and orange principles are very soluble in luke-warm alcohol at 85 percent, wherein purpurin and pseudopurpurin are nearly insoluble. The yellowis soluble in benzol, in which the orange is insoluble. Purpurin is tolerablysoluble in boiling alcohol, from which, on cooling, it is deposited in crystals,whilst pseudopurpurin is almost insoluble in the same liquid. The yellowmatter, xanthopurpurin, is contained in commercial purpurin in small tracesonly, not exceeding 1 part in 500. The orange matter and purpurin properform about one quarter of the commercial substance in equal proportions,whilst the entire residue is made up of pseudopurpurin. To obtain pure purpurinthe easiest method is to place a little of the commercial product in a porcelaincapsule, and to treat it on the sand-bath as already directed for alizarin.Purpurin only sublimes, leaving a bulky carbonaceous mass at the bottom ofthe capsule. During the sublimation pseudopurpurin and the orange matterare partly converted into purpurin. Another method is to heat commercialalizarin, previously well washed with luke-warm alcohol, in a sealed tube alongwith alcohol up to 200° C. By this process purpurin is obtained in beautifulcrystalline needles, whilst a black powder settles at the bottom of the tube.In this instance also pseudopurpurin is converted into purpurin.

The characters of purpurin are :—colour redder than that of alizarin ; itsublimes at 250® C., but always with partial decomposition, leaving behind acarbonaceous residue. The crystals differ from those of alizarin, andcommonly resemble the feather of a quill. When dissolved in boiling alcohol,they are re-deposited, on cooling, in crystalline needles, often 1 centim. inlength, of a beautiful red, slightly verging upon orange. If dissolved in alcoholwithout previous sublimation, they form, on cooling, very small groups of minuteacicular crystals. There is, however, no difference in their composition.

Purpurin is rather more soluble in boiling water and boiling alcohol thanalizarin, but is otherwise soluble in the same liquids. Purpurin consists ofC14H8O5, or C I4 H 5 0 2 ( 0 H) 3 . The carbon and hydrogen are given respectivelyat 66-67 and 370 per cent by Wolff and Strecker, but by Debus at 66*38 and 3*87,and by Schiffer and Schutzenberger 65*93 and 3 ' 2 9 * Potassa, soda, and ammoniadissolve purpurin, yielding characteristic poppy-red solutions, quite distinctfrom the almost blue solutions yielded by alizarin under the same conditions.The presence of 10 per cent alizarin mixed with purpurin can be detected bysolution in alkaline liquids, since the blue shade becomes distinctly perceptibleon dilution with water. Alkaline carbonates and salts, which in solutionexhibit a basic reaction, e.g., borax, dissolve purpurin, yielding red solutions.Alum water dissolves purpurin far more readily than alizarin, and the redsolution does not, on cooling, deposit a sediment of purpurin, whilst alizarinis, in great measure, thrown down on cooling. The lakes containing bothsubstances together yield purpurin when boiled with solution of carbonate ofsoda. The combinations of purpurin with bases have great similarity withthe corresponding alizarin compounds. The alkaline purpurates are solublein water; those of the alkaline earths and metallic oxides insoluble. Theformer are nearly black, yielding red solutions. Purpurate of soda canbe obtained in crystals by a similar process to the alizarate. The aluminalake of purpurin is a full red, without the least trace of blue. The iron-lakes