RUBIAN.

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is called erythrozym.* This ferment may be obtained by the addition ofalcohol to an aqueous infusion of madder, when a curdy precipitate is formed.If this is added to a solution of rubian, the latter in the course of a few hoursbecomes a bright brown jelly, containing the tinctorial principles in an insolublestate. Rubian is very difficult to obtain pure, being very liable to decom-position and not precipitable by any metallic salt, except the subacetate oflead. The separation of rubian from chlorogenin requires very nice manipula-tions. To effeCt this separation Schunck makes use of the great affinity ofrubian for porous bodies, especially animal charcoal. He digests a hot decoCtionof madder with animal charcoal, and washes the latter on a filter with coldwater until a small quantity of the washings, when boiled with hydrochloricacid, ceases to yield a greenish colouration. Thus the chlorogenin isremoved. The charcoal is next exhausted with boiling alcohol, which extractsthe rubian. The alcoholic solution is evaporated to dryness, taken up withwater, again treated with animal charcoal, and the latter again exhausted withalcohol.

This treatment is repeated until the chlorogenin is entirely removed. Thealcoholic solution is finally evaporated to dryness, taken up with water, and thisaqueous solution is first treated with a solution of neutral acetate of lead,which precipitates any impurity. It is filtered, and then precipitated withbasic acetate of lead. The precipitate formed is decomposed with sulphurettedhydrogen or dilute sulphuric acid, and after removal of the lead compoundrubian is left dissolved in the water. The substance in this state still retainsmineral matter, and is therefore not quite pure. Nevertheless, we may drawconclusions regarding the tinctorial matter pre-existent in the madder rootduring its growth. Rubian is a glucoside, or perhaps a mixture of glucosides,capable of being decomposed by acids, alkalies, and ferments into colouringmatters and sugar. Since Dr. Schunck’s analysis shows the formula to beCidH^Os, the following equation represents the reaction which takes place :—

Ci6Hi608+H 2 0 = CioHgOg + C6H12O6Rubian. Alizarin. Glucose.

We shall presently see that the constitution of rubian is scarcely so simple. Itprobably contains several glucosides capable of yielding alizarin and pseudo-purpurin, &c. The composition of all these colouring matters approachesclosely that of alizarin. Schunck has never found purpurin among theproducts of decomposition of rubian, whether this was affeCted by an acid, analkali, or a ferment. He always, however, found a yellow crystalline colouringmatter, first discovered by Runge, and named by him “madder orange.” Thenature of this colouring matter varies according to the agent employed, orrather, acids give rise to one substance, alkalies to another, and ferments toa third. These three substances, though essentially distinct, have someproperties in common. Two of them, rubiacin and rubiadin, can easily beidentified by their reactions. Rochleder’s researches are chiefly valuable fromthe faCt that he has succeeded in isolating the alizarin-glucoside in a crystallinestate, and has named it ruberythric acid. It occurs mixed up with rubian.

* The nitrogenous principles met with in madder are extremely prone to change, and are inthis respedt as difficult to study and to obtain in a pure state as some of the biliary principles.It is always the moUcule en mouvement , and hence its protean properties.