i88

DYEING AND CALICO PRINTING.

for even the mostjfeeble acids, that the dull colour of its alcoholic solutionrapidly changes to purple under the influence of the carbonic acid of thebreath. Mauveine is decolourised by nascent hydrogen, but its original colouris instantaneously restored by the oxygen of the air. The mauve of commerceis usually a brownish violet-coloured paste, very sparingly soluble in coldwater, somewhat more so in hot water, but readily soluble in alcohol, wood-spirit, aceton, in the acetic, sulphuric, hydrochloric, and tartaric acids, inglycerine and aniline. This substance 'may be obtained in crystalline formwhen its solutions are evaporated to dryness. The crystals exhibit, especiallyafter having been washed with some ammoniacal water, a brilliant greencolour. Mauve is precipitated from all its solutions by water, especiallyif the latter contains neutral alkaline salts, caustic alkalies, or metallic salts.If the paste or solid mass is placed upon a strongly-heated metallic plate redvapours are given off, and volatilisation appears to take place; but evenin vacuo no sublimate is obtainable. When mauve is treated with rather con-centrated hydrochloric or sulphuric acid it is converted into a blue-colouredmass, which a larger addition of acid renders green. On the addition of waterthe blue colour is first brought out again, and after a while the violet isrestored. When mauve is boiled with dilute nitric acid there is formeda yellow-coloured liquid, and a reddish pulverulent mass scarcely soluble inwater is precipitated. Chlorine water discolours the alcoholic solution, butits colour is restored by the adtion of sulphuric acid. According to M. Scheurer-Kestner, the composition of mauve is represented by the formulaand it therefore only differs from rosaniline (C 20 H I9 N 3 ) by containing less H.This view is not that of the celebrated discoverer of mauve, Mr. Perkin,who says that the material obtained by the adtion of bichromate of potassaupon sulphate of aniline is the sulphate of an entirely new base, mauveine,C 27 H 24 N 4 . This base is prepared from the crystalline mauve of commerce byadding to its boiling solution a solution of caustic soda. By this proceedingthe purple colour of the solution of the mauve changes diredtly to a violetblue, and when the solution is left standing a crystalline substance is deposited,which after having been first washed with alcohol, and next with water,exhibits after drying a brilliant blackish powder not unlike oligistic iron ore.Mauveine is soluble in alcohol, yielding a violet-coloured solution, which onthe addition of an acid is converted into a purple colour. Mauveine is almostinsoluble in ether and benzol, and is a strong base which even decomposesammoniacal salts. When subjedted to a high temperature decomposition takesplace, and an oily basic substance is obtained distindt from aniline. Mauveineforms a series of salts, all of which have been carefully studied and describedby Mr. Perkin, and which are nearly all rather hygroscopic. The salts of themauveine, or indisine of commerce, are usually prepared by means of theoxidising adtion of suitable materials upon the salts of aniline of commerce(mixtures of aniline and toluidine) in aqueous solution. The method adoptedfor the preparation of mauve is as follows :—ioo kilos, of heavy aniline are mixedwith 54 kilos, of concentrated sulphuric acid and 2 kilos, of water. Theacid thus diluted is added to the aniline little by little with constant stirring.When the whole has been poured in, the mixture is heated and stirred so asto obtain a homogeneous liquid, and is then allowed to cool. When coldadd 140 kilos, of bichromate of potash dissolved in the smallest possible