23B

DYEING AND CALICO PRINTING.

lime water. This precipitate is decomposed with acetic acid, and the solutionboiled with wool mordanted in alum to remove purpurin. The solution isevaporated to dryness, taken up with alcohol, and again precipitated with analcoholic solution of acetate of lead. The precipitate thus obtained iswashed with alcohol, and decomposed with sulphuretted hydrogen.*

Higgin exhausts madder with boiling water, precipitates the matterssparingly soluble in water with very dilute sulphuric acid, saturates withcarbonate of soda, and afterwards digests the fluid with hydrate of alumina,in order to separate alizarin. Baryta water is next added, and afterwardssubacetate of lead. The precipitate is well washed and decomposed withsulphuretted hydrogen. The produdt thus obtained still contains chlorogenin,since on being boiled with acids a green precipitate ensues.

According to Schunck, the aqueous extradf of madder, made either withcold or tepid water undergoes spontaneous decomposition, either with orwithout access of air. A flocculent yellow precipitate is formed, whichcontains all the colouring matter of the infusion. Schunck ascribes the bittertaste, and the tindlorial properties of the extract, to a substance which henames Rubian, and considers the Xanthin of Kuhlmann, Runge, and Higginsto be a mixture of rubian, chlorogenin, and glucose. 'Rubian, properly pre-pared, is a hard, amorphous, brittle substance, glossy when in thin laminae.Its colour is deep yellow, or brown when seen in large masses. It is per-manent in the air, easily soluble in water, sparingly in alcohol, and insolublein ether. It has an intensely bitter taste. The aqueous solution is pre-cipitated only with subacetate of lead. With concentrated sulphuric acid rubianyields a blood-red solution, decomposable by heat. Nitric acid does not affedtcold solutions of rubian, but, on boiling, pbthalic acid is formed. Normalphosphoric acid and the organic acids are without any adtion upon rubian,even at the boiling-point. Soda converts the yellow solution to a blood-red,which, on boiling, becomes purple. Acids then precipitate from the solutiona reddish-orange substance, and the liquid becomes colourless. At a highertemperature the glucoside which forms the rubian is split up. Ammonia alsomodifies the yellow solution to blood-red, but no further change ensues onboiling. Lime and baryta water throw down rubian as a deep red substance,soluble in water. Magnesia converts the yellow solution of rubian to a deepred, the alkaline earth becoming dissolved. Carbonates of lime and barytahave no adtion; alumina and the hydrated peroxide of iron and oxide ofcopper throw down rubian completely from its solutions. In presence of analkali, rubian reduces the salts of gold, but salts of silver and copper are notadted upon under the same conditions. Rubian fuses when heated, and burnson ignition, leaving from 6 to 8 per cent of ash, consisting of carbonate of lime.If heated to 130° C. in a tube, it yields orange vapours, composed chiefly ofalizarin. When rubian is boiled with dilute hydrochloric or sulphuric acid ityields, on cooling, a flocculent orange matter, insoluble in these acids. In theliquid there remains a kind of sugar capable of fermentation and of reducingalkaline solutions of copper. Rubian undergoes a similar decomposition bythe adtion of a peculiar nitrogenous compound which exists in madder, and

* It should be kept in view that too many of those who have experimented with madderhave entirely forgotton two essential points:—To ascertain the time that the sample hadbeen in cask, and the precise locality and manufactory from which it originated.