Dr. Schunck on Rubian and its Products of Decomposition. 215 



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. 



Persoz* asserts the probability of this view in the following 

 words : — " We may hence venture to conclude that the colour- 

 ing 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 isolated 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 regards 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 

 composition 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 Mad- 

 derf, 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 occasion, that the 

 xanthine of Kuhlmann and other investigators is not a pure sub- 

 stance, but a mixture of two distinct substances. This fact how- 

 ever does not affect the correctness 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 xan- 

 thine is easily ascertained by the deep yellow colour and in- 

 tensely 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 morerapidly when heated to 120° or 130° I^ahv.,, 

 the Eanthine gradually disappears and there is formed a gelatinous 

 or fioccuieiit substance, which possesses all the tinctorial power 

 originally belonging to the infusion, while the liquid has lost 

 all trace of any such power, and that as alizarine is the only 



• Troitf de V Impression des Tissus, t. i. p. 501. 

 t Philosophical Magazine tor (Jet. 1848. 



