DYEING AND CALICO PRINTING.

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clear liquid is decanted, and the insoluble residue frequently washed withwater; the clear solution thus obtained contains as its main constituentalloxan and alloxantin; the former of these substances is entirely convertedinto alloxantin by means of the reducing action of protochloride of tin, andprecipitated in the shape of alloxantin ; this precipitate having settled downthe clear supernatant liquid is withdrawn, and the pasty mass thrown on alinen filter and washed with acidulated water. After having been carefullydried and reduced to powder, it is placed in a porcelain basin, set in anotherbasin containing liquid ammonia, and put aside in a warm place until thepowder has been entirely converted into a brilliant purple mass. In otherwords, it has been converted into murexide; since alloxantin forms, when itis in an atmosphere containing ammonia and water, murexide (purpurate ofammonia*).

Pure murexide when dry is a brilliant crystalline powder of metallic lustre anda golden greenish hue akin to that of the wings of Spanish flies. Placed betweenthe eye and the light these crystals appear red, and when pulverised thepowder is red. At ioo° the crystals lose 1 molecule of water. Murexide isinsoluble in alcohol and ether; sparingly soluble in cold water, to which itimparts a reddish hue ; in hot water the solubility is greater. Murexide isfar more soluble in solution of nitrate of lead, wherewith it does not undergodouble decomposition. The purpurates of baryta, silver, mercury, and lead(if acetate be used) are insoluble in water. Murexide dissolves in an aqueoussolution of caustic potassa, yielding a most magnificently blue solution,which becomes colourless on the application of heat. Murexide is now nolonger used for dyeing or calico printing, having been superseded by theaniline colours. It was met with in trade in three different conditions,viz., as paste, as powder, and in crystals. The manufacture of this articlerequired great skill and nicety of management, and, consequently, the sub-stance was always expensive. Murexide was applied as a dye to silk andwool by mixing with corrosive sublimate, acetate of soda, and acetic acid.For printing, a mixture of murexide with nitrate of lead or acetate of zincproperly thickened is applied on cotton fabrics, which are then allowed to dryfor a day or two, when the colour is fixed by passing them through a mixtureof corrosive sublimate, acetate of soda, and acetic acid. A modification ofthis process was used very successfully some years ago by mixing a thickenedsolution of murexide in nitrate of lead, with a thickened solution of bichlorideof mercury (these solutions do not precipitate each other for some twenty-four hours, and then only imperfectly). This colour was then printed on thecloth and aged two or three days, and fixed by simply running through asolution of acetate of soda. This allowed murexide colours to be printed alongwith, and after, other colours which would have been spoiled by runningthrough a solution of bichloride or pernitrate of mercury, which latter saltwas chiefly employed. Murexide on woven tissues can be detected—

1. By its beautiful and brilliant rose or purplish rose amaranth, whichbehaves with reagents in the following manner:—(a). The colour is destroyedby dilute mineral acids (hydrochloric, nitric, and sulphuric); ( b ). Causticalkalies also destroy the colour, which, however, turns first blue; washing

Purpuric acid is not known in isolated state.