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DYEING AND CALICO PRINTING.

are either violet or black. When hydrochloric acid is added to a recent solutionof purpurin in ammonia, the colour is thrown down unaltered in the shape oforange-yellow flocks. If the solution has been kept even for twenty-fourhours, the precipitate resulting from the addition of hydrochloric acid is adeep violet. The same result is obtained by heating the ammoniacal solutionto 100° C. This precipitate gives off ammonia when heated with caustic soda,proving that an amide has been formed, purpuramide or purpureine. It is solublein boiling alcohol, yielding a deep violet-red solution, and on evaporationforms crystals exhibiting a green refledtion like those of murexide. Thissubstance dyes wool and silk an amaranth shade without any mordant. Itsformula is Ci 4 H g N 0 4 , or C I4 H 5 NH 2 (HO)202. When a mixture of crystallisedpurpurate of soda, iodide of ethyl, and alcohol is heated in a sealed tube to150° C., there is formed iodide of sodium, and a red crystalline substancesparingly soluble in alcohol. Its formula is Ci 4 H5(C 2 H 5 0)30 2 .

Pseudopurpurin is almost insoluble in boiling alcohol, but soluble in hotbenzol, from which it separates on cooling in fine acicular crystals of a brick-redcolour. Heat, as well as treatment with alcohol at high temperatures in a sealedtube, convert pseudopurpurin into purpurin. Pseudopurpurin dissolves inalkalies with a red colour. With ammonia it forms an amido-derivativc,in a similar manner to purpurin. The formula of pseudopurpurin isC I4 H 4 (H 0 ) 4 0 2 .

The orange matter is insoluble in boiling benzol; very soluble in luke warmalcohol, from which it is deposited, on cooling, either as a thick granularcurdy mass, or again as orange scales. This depends on the concentration ofthe solution. This substance is partially converted by the adtion of dry heatinto purpurin. Its formula, according to Schiitzenberger, is C 2 oHi 60 g .Purpurin, pseudopurpurin, and the orange matter yield with mordantsshades resembling those of alizarin, but without a blue refledtion. Goodsdyed with purpurin and the orange matter resist boiling soap-lye tolerablywell, but the shades produced by pseudopurpurin fade away. The power toresist clearing varies, therefore, inversely as the amount of oxygen in thecolour.

The yellow colour, purpuroxanthin, is soluble in alcohol and benzol,sparingly soluble in water, and sublimes when heated almost without decom-position. With aluminous mordants it yields a dull and fugitive yellow, whichis destroyed by the per-salts of tin and by clearing. It is readily obtained by theredudtion of purpurin, pseudopurpurin, or the orange matter, by heating to180° C. in a sealed tube along with aqueous teriodide of phosphorus. It ismore easily prepared by adding some protochloride of tin to a boiling solutionof crude purpurin in caustic soda. The solution loses its red colour andbecomes orange. The addition of an excess of hydrochloric acid throwsdown the yellow matter. It is then thrown on a filter, washed, and purifiedby sublimation and crystallisation from alcohol.

Turning now to the researches of Schunck on this subjedl, we maysummarise his results as follows :—

a. By splitting up the rubian under the influence of boiling dilute hydro-chloric or sulphuric acid he obtains—(1) alizarin; (2) rubianin, a lemon-yellow matter, crystallisable, and more soluble in water, but less so in alcohol