134 Dr. Schunck on the Colouring Mailers of Madder. 



colouring matters, two kinds of fat, pectic acid and a substance of 

 an intensely bitter taste, which I am as yet unable to refer to any 

 known class of bodies. The whole quantity of colouring matter con- 

 tained in the aqueous extract of madder is precipitated by the addi- 

 tion of a strong acid. In proof of this I took a quantity of the aque- 

 ous extract, added sulphuric acid, separated the brown precipitate by 

 filtration and removed the excess of acid with cold water, and then 

 boiled It with water, into which a small piece of mordanted cloth 

 was introduced. The cloth assumed the same colours which it Avould 

 have done with madder. To the fluid to which acid had been added 

 I put chalk until all the acid was saturated, and I then found after 

 filtering that it communicated no colour whatever to mordanted 

 cloth. 



Of the two colouring matters, one is Robiquet's Alizarin, and the 

 other I shall call Rubiacin. Both are contained in the brown pre- 

 cipitate produced by acids in the aqueous extract of madder. In 

 order to obtain them, this brown precipitate is first treated with 

 boiling alcohol until nothing more is dissolved. A dark brownish- 

 purple, somewhat gelatinous mass is left behind, consisting principally 

 of pectic acid. The alcoholic fluid, which contains the two colouring 

 matters together with the fats, has a dark brownish-yellow colour. 

 After being distilled and then evaporated to dryness, a residue of a 

 dirty orange colour remains. This residue is placed on a filter 

 and washed with cold water, until the percolating fluid, which is at 

 first yellow, becomes colourless. On evaporation this fluid leaves a 

 transparent yellow substance with a bitter taste, mentioned above. 

 This substance is soluble in pure water, but insoluble in water con- 

 taining acids, and hence it is precipitated on adding acid to the 

 aqueous extract of madder; but on washing the precipitate with 

 water, after the acid has been removed it begins to dissolve. In 

 order to obtain it, therefore, the brown precipitate must only be 

 washed so long as it still contains free acid. I shall call this sub- 

 stance Rubian. The mass left undissolved by cold water is then 

 treated with boiling water, and the fluid is filtered boiling hot. On 

 cooling it deposits a quantity of red flocks, which consist of alizarin 

 mixed with fat. This process must be repeated until the boiling 

 fluid deposits nothing more on cooling. If any rubian be still left 

 in the mass on treating with boiling water, the filtration of the boiling 

 fluid is very much impeded, and it is therefore advisable to remove 

 this substance completely with cold water previously to treating with 

 hot water. The whole of the alizarin dissolved in the boiling water 

 is deposited on cooling, but mingled with fat, which probably ac- 

 companies it through the filter in a state of suspension produced by 

 the heat of the boiling fluid. This fat disguises its properties very 

 much, and has been the cause, in all previous investigations, of ali- 

 zarin never having been obtained in a state of purity except through 

 the agency of heat, which has always left it doubtful whether it ex- 

 isted in the plant as such, or was formed by the action of heat from 

 some other substance. I hope to establish satisfactorily its existence 

 as a constituent of the madder root, and also the fact of its being a 



