Dr. Schunck on Rubian and its Products of Decomposition. 361 



is disengaged, and the substance is decomposed. Concentrated 

 nitric acid dissolves it on boiling with a disengagement of nitrous 

 acid, forming a yellow liquid, from which nothing separates on 

 cooling. Dilute nitric acid does not affect it sensibly on boiling. 

 It is almost insoluble in boiling water, but readily soluble in 

 boiling alcohol with a dark brownish-yellow colour, and is again 

 deposited, on the alcohol cooling, as a brown powder, which is 

 its most characteristic property. It is soluble in alkaline liquids 

 with a dirty brownish-red colour, and is reprecipitated by acids 

 in brown flocks. If it be mixed with alizarine, then its solutions 

 in alkalies have a reddish-purple colour. The ammoniacal solu- 

 tion loses its ammonia on evaporation, and leaves the substance 

 behind as a brown transparent pellicle. The ammoniacal solu- 

 tion gives precipitates with the chlorides of barium and calcium. 

 The alcoholic solution gives dark brown precipitates with the 

 acetates of lead and copper, as I mentioned before. When it is 

 free from alizarine, it does not communicate any colour to mor- 

 danted cloth, and is therefore no colouring matter in the usual 

 sense. 



In the opinion of most chemists who have examined madder, 

 this root contains two distinct colouring matters, viz. alizarine 

 and another, to which the names of purpurine, oxylizaric acid 

 and madder-purple have been applied by different chemists. This 

 opinion has been advocated with considerable ability by MM. 

 Wolff and Strecker. I have however reason to suppose that 

 purpurine is in fact no distinct substance, but a mixture of ali- 

 zarine and verantine. The latter substance accompanies almost 

 all the products which are obtained from madder, and it is this 

 body which renders them so difficult to purify. It adheres so 

 pertinaciously to alizarine, as to induce the belief that the two 

 actually form a chemical compound. The mixtures of the two 

 vary in appearance from that of dark red crystals to that of a 

 red crystalline powder. In these mixtures the verantine may 

 easily be detected by dissolving in alcohol and adding acetate of 

 copper, which precipitates the verantine, as before described. It 

 also accompanies rubianine and renders it difficult to crystallize, 

 as I mentioned above, and I have never been able to obtain rubi- 

 retine without some trace of it. As a characteristic of purpurine 

 is mentioned its property of giving a cherry-red solution with 

 alkalies, having none of the violet appearance belonging to alka- 

 line solutions of alizarine ; and also its forming, when treated 

 with boiling alum-liquor, a red opalescent solution, from which 

 it separates again in orange-coloured flocks on the solution cool- 

 ing. Now by adding to a solution of alizarine in caustic alkali 

 a little verantine, the beautiful violet colour of the solution may 

 be instantly changed to reddish-purple ; and by dissolving in it 



