434 MR, SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 
mixtures, and some of them in the main identical, has been satisfactorily proved by 
late investigators. But there still remain a number, which, though extremely similar, 
have properties sufficiently marked to entitle them to be considered as distinct. 
In my papers on the colouring matters of madder*, I have described four sub- 
stances derived from madder, only one of which is a true colouring matter, but all 
of them capable, under certain circumstances, as for instance in combination with 
alkalies, of developing red or purple colours of various intensity. To seek for a 
common origin for these various bodies so similar to one another and yet distinct, is 
very natural, and the discovery of it no improbable achievement. 
PfiRSOZ'f' asserts the probability of this view in the following words: — “We may 
hence venture to conclude that the colouring matters which we extract from fabrics 
dyed with madder, as well as the alizarine which is obtained by submitting the pro- 
ducts derived from madder to sublimation, do not exist ready formed in this root, 
and are only products derived from another substance which has not yet been iso- 
lated From numerous experiments which I have made on this subject, it follows 
that the colouring matter of madder may be compared, in respect to the derivatives 
to which it gives rise, to tannin, so that I do not despair of being able, as far as re- 
gards their metamorphoses, to establish a parallel between the products derived from 
madder and those obtained from tannin. If it should be possible to confer on the 
former that tendency to assume regular forms with which the latter are endowed, 
the separation of the proximate colouring or colour-giving {colorable) matters of 
madder will be easy, and it will thus be possible to establish their elementary com- 
position and thence their relation to one another.” 
To Mr. J. Higgin is due the merit of having first called attention to the fact, that 
important changes take place during the process of dyeing with madder, which can 
only be explained by supposing that an actual formation of colouring matter takes 
place during the process. In his paper ‘On the Colouring Matters of Madder;}:,’ 
Mr. Higgin has detailed his experiments on that peculiar substance discovered in 
madder by Kuhlmann and called by him Xanthine. I have shown, on a former occa- 
sion, that the xanthine of Kuhlmann and other investigators is not a pure substance, 
but a mixture of two distinct substances. This fact however does not affect the cor- 
rectness of Mr. Higgin’s conclusions, the general accuracy of which I shall have 
great pleasure in confirming in the course of this paper. The presence of xanthine 
is easily ascertained by the deep yellow colour and intensely bitter taste which it 
communicates to cold water. Guided by these two tests, Mr. Higgin arrived at the 
conclusion, that in an infusion of madder, made with cold or tepid water, when left 
to itself, or more rapidly when heated to 120° or 130° Fahr., the xanthine gradually 
disappears and there is formed a gelatinous or flocculent substance, which possesses 
all the tinctorial power originally belonging to the infusion, while the liquid has lost 
* See Reports of the British Association for 1847 and 1848. 
t Traite de ITmpression des Tissus, t. i. p. 501. t Philosophical Magazine for Oct. 1848. 
