450 MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 
limate without a trace of anything crystalline. When however it contains alizarine, 
as it very often does, it gives on being heated a crystalline sublimate consisting of 
the latter substance. It dissolves in concentrated sulphuric acid with a brown 
colour, and is reprecipitated by water in brown flocks. On heating the solution in 
concentrated sulphuric acid it becomes black, sulphurous acid is disengaged, and the 
substance is decomposed. Concentrated nitric acid dissolves it on boiling with a dis- 
engagement 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 in- 
soluble 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 ammo- 
niacal solution loses its ammonia on evaporation, and leaves the substance behind as 
a brown transparent pellicle. The ammoniacal solution gives precipitates with the 
chlorides of barium and calcium. The alcoholic solution gives dark brown precipi- 
tates with the acetates of lead and copper, as I mentioned before. When it is free 
from alizarine, it does not communicate any colour to mordanted cloth, and is there- 
fore 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 o^ pur- 
purine, 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 alizarine 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 in- 
duce 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 de- 
scribed. It also accompanies rubianine and renders it difficult to crystallize, as I 
mentioned above, and I have never been able to obtain rubiretine 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 alkaline 
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 cooling. 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 red- 
dish-purple; and by dissolving in it still more of that substance the colour may be 
rendered cherry-red, these colours being evidently mixtures of the violet due to aliza- 
