436 MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOxMPOSITION. 
was no longer capable of dyeing. The tinctorial power was also destroyed by the 
addition of hydrate of alumina, magnesia, protoxide of tin and various metallic 
oxides, but not by carbonate of lime or carbonate of lead. In all cases in which the 
property of dyeing in the extract was destroyedj I invariably found that its bitter 
taste and bright yellow colour were lost. Now in my former papers on this subject, 
I have shown that the intensely bitter taste of madder and its extracts is due to a 
peculiar substance, to which I have given the name of Ruhian ; and as it appeared 
from these preliminary experiments that this substance, though itself no colouring 
matter, is in some way concerned in the changes whereby a formation of colouring 
matter is induced in aqueous extracts of madder, I proposed to myself to examine 
its properties and products of decomposition more in detail than I had hitherto 
done. 
The first step necessary to be taken for the attainment of this object, was of course 
to find a method of procuring this substance in quantities sufl&ciently large for the 
purposes of examination. I was at the commencement however far from appre- 
ciating the difficulties with which its preparation in a state of purity is attended. 
The process which I had formerly described, by precipitation with sulphuric acid, is 
not well adapted to the purpose, since rubian in a state of perfect purity is not pre- 
cipitated by sulphuric acid, besides which it is easily decomposed by an excess of 
that acid. Neither is it precipitated by any metallic salt, with the exception of basic 
acetate of lead, which, from the circumstance of its precipitating also other sub- 
stances from the extract, is not applicable to the purpose. It is decomposed by 
alkalies and alkaline earths. Even bicarbonate of lime exerts a decomposing effect 
on it in conjunction with the oxygen of the atmosphere. These substances must 
therefore be discarded in its preparation. Besides its great tendency to decomposi- 
tion, there is another circumstance which presents obstacles to almost all attempts 
to prepare rubian in a state of purity. There is no investigation of madder which 
does not make mention of a substance, which when its solution in water is mixed 
with sulphuric or muriatic acid and boiled, gives rise to the formation of a dark 
green powder. To this substance, which possesses no bitter taste, and is in fact 
devoid of any characteristic property except the one mentioned, I have restricted the 
name of xanthine. The xanthine of most other chemists is however a mixture of rubian 
with this substance, and possesses therefore the bitter taste of the former, while 
showing the characteristic behaviour of the latter towards acids. To avoid confusion, 
I shall no longer employ the name of xanthine, and I shall call the substance which 
gives the green powder with acids Chlorogenine. Now these two substances, though of 
very different nature, behave similarly towards many reagents. If, for instance, basic 
acetate of lead be added to a watery extract of madder, according to the method pro- 
posed by Berzelius for the preparation of xanthine, and adopted with a slight modi- 
fication by Mr. Higgin, there is produced a red precipitate, which after being washed 
and decomposed with sulphuretted hydrogen or sulphuric acid, gives a solution con- 
