682

DYEING AND CALICO PRINTING.

If binitro-anthraquinon is boiled for a long time with aniline, the lattertakes a deep red-brown colour, and the whole dissolves in hot water with thesame colour. If, instead of water, hydrochloric acid is employed, the liquidis coloured at first a dirty yellow, then a red, with the formation of blackresinous flocks, which dissolve in bisulphide of carbon with a splendidmagenta colour. This colour cannot be withdrawn from the sulphide ofcarbon either by pure or by acidulated water.

Binitro-anthraquinon readts energetically upon cyanide of potassium,forming, according to circumstances, violet-brown or orange-red compounds.If, according to Bcettger and Petersen, binitro-anthraquinon is dissolved in16 or 18 parts of concentrated sulphuric acid, and if heat is applied, at aboutthe temperature of 200° C., there is an abundant disengagement of sulphurousacid, and the colour of the liquid changes from a yellowish-brown to a deepred-brown. The readtion becomes more and more brisk, so that it is necessaryto withdraw the heat for some time. When the violence of the adtion hasceased heat is again cautiously applied, until the escape of sulphurous acidhas discontinued.

The mass is allowed to cool, and is thrown into cold water, when it depositsdeep reddish-brown flocks, which, after being filtered and washed, dissolve indilute alkaline solutions with a deep violet-blue colour, and are re-precipitatedon the addition of an acid. This substance may be purified by re-crystallisa-tion from alcohol, when it is obtained in small agglomerated granules of adeep violet, or in brilliant incrustations of a brownish-violet with metallicrefledtions. This colour is sparingly soluble in water, to which it imparts thecolour of peach-blossom. It dissolves freely in alcohol, ether, and glycerin,forming solutions of a splendid violet-red. It dissolves in acetic acid with amagenta-red, in sulphuric acid with a hyacinth-red, and in alkaline solutionswith a violet-blue. It dyes cotton a violet, without mordants.

30. Artificial Isopurpurin.—This isomer of purpurin has been recentlydiscovered by Auerbach in the produdt prepared by Gessert Bros., of Eberfeld,under the name of alizarin, with a yellow refledtion, or purpurin, because itproduces—both in dyeing with an aluminous mordant and as a steam-colourin printing—shades similar to those obtained with the natural purpurin frommadder (see p. 247).

This so-called yellow alizarin or artificial purpurin appears in form of aslightly liquid homogeneous paste, containing 15 per cent of dry matter, andsoluble in dilute caustic alkaline lyes, yielding a solution of a splendidreddish-violet colour.

To extrad isopurpurin from this substance it is dissolved in ammortia, thesolution is mixed with hydrate of baryta, and the precipitate formed is boiledwith water as long as the filtered liquid has a red colour. From this aqueoussolution the isopurpurin is precipitated with an acid, filtered, washed, and thesame treatment is repeated. If the isopurpurin is precipitated with sulphuricacid, it may be isolated by treatment with alcohol, the precipitate composed ofsulphate of baryta and of isopurpurin. The latter dissolves very readily.

Isopurpurin prepared in this manner, repeatedly purified with hydrate ofbaryta and crystallised from alcohol, has the same composition as the purpurinfrom madder.

Isopurpurin is of an orange-red, and presents all the properties of alizarin,but it dissolves in the hydrate of soda with a more violet-red colour. It is