244

DYEING AND CALICO PRINTING.

of containing 50 grms. A few decigrms. of material are sufficient for theexperiment. A piece of clean white filtering-paper is placed on the top of thecapsule, which is next covered with its lid and heated on the sand-bath to250° C. After the lapse of half an hour the interior of the capsule will befound lined with long, beautiful needles. At the bottom there remains aporous, bulky, carbonaceous substance, containing hardly a trace of alizarin,when pure alizarin has been experimented with. When alcoholic extract ofmadder or garancin has been submitted to sublimation the alizarin is oftensoiled by empyreumatic substances, and requires to be re-sublimed. Thecolour exhibited by alizarin varies according to the conditions under which ithas been obtained. It is sometimes a dark red substance, usually ratherorange, but sometimes yellow, especially if it is crystallised from an acidsolution,—as, for instance, when glacial acetic acid has been applied. Purecold water only dissolves an insignificant trace of alizarin, but if the watercontains any alkaline matter it becomes yellowish or orange by a trace ofalizarin. According to Plessy and Schutzenberger, 100 parts of water, atioo° C., dissolve 0*034 part of alizarin; at 150° C., 0*035; at 200 ° C., 0*82;at 225 0 C., 1*70 parts ; at 250° C., 3*16. Up to 200° C., therefore, thesolubility increases slowly, but becomes far greater on approaching thesubliming point of alizarin. The solubility of alizarin in alcohol is notperfectly determined. At the ordinary temperature of the air it is more solublein alcohol than in water. When pure, a boiling alcoholic solution of alizarinexhibits an orange-yellow colour, and on cooling deposits long needle-shapedcrystals. Alizarin is readily soluble, especially with the aid of heat, in ether,wood-spirit, benzol, oils of tar, naphtha, and petroleum, spirits of turpentine,sulphide of carbon, glycerine, chloroform, and acetic acid. The hot saturatedsolutions of some of these deposit alizarin in crystals on cooling. An aqueoussolution of alum does not, when cold, dissolve any alizarin. It dissolves tosome extent in a hot solution, but is re-deposited on cooling. Strong sulphuricacid dissolves alizarin without decomposition or change. Water precipitatesthe colouring matter from this solution unaltered, in the shape of an orangeflocculent precipitate. The solution of alizarin in sulphuric acid is notaffe&ed by a temperature of 200° C. As regards the composition of alizarinand the formulae assigned it various views prevail. That given by Dr.Schunck, C I4 H io 0 4 , agrees best with the analysis of pure specimens, and isconfirmed by the experiments of Graebe and Liebermann on the artificialformation of alizarin. Schunck deduced his formula from the examination ofrubianic acid, the glucoside of alizarin. This acid gives a potash salt crystal-lising in needles, by means of which the above-mentioned chemist was enabledto determine the atomic weight of the acid. It contained C 2 6, and hencealizarin must have Ci 4 . Many chemists were led astray by supposing, withLaurent, that there must be a close relationship in composition betweenalizarin and naphthalin.

Alizarin is a weak acid capable of combining with bases. With alkalies ityields salts readily soluble in water, sparingly soluble in alcohol, and insolublein ether. The aqueous solutions exhibit a splendid violet-blue colour. Crys-tallised alizarate of soda is readily obtained by adding an alcoholic solution ofsoda to alcohol in which alizarin is kept suspended, and immediately afteradding a quantity of ether to the mixture, so that it may form a separate