MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 435 
all trace of any such power, and that as alizarine is the only substance contained in 
madder capable of dyeing, the xanthine must, during this process, have been changed 
into alizarine. Mr. Higgin found that this process is completely arrested by heating 
the infusion to the boiling-point, or by adding alcohol, acids or acid salts to it, and 
hence he concludes that the decomposition of the xanthine is caused by the action of 
a peculiar ferment contained in madder, and which is extracted together with xan- 
thine by cold water. Mr. Higgin did not however succeed in converting his xanthine 
into alizarine or effecting any change in it by means of fermentation, in consequence, 
as he supposed, of not being able to obtain the exciting substance in a soluble and 
consequently active condition. His inferences were all derived from experiments 
made by either removing from an extract of madder the xanthine contained in it, or 
by adding to it an additional quantity of that substance, and then ascertaining the 
effects produced by dyeing in the usual way with liquids thus artificially prepared. 
By the action of sulphuric acid on xanthine, Mr. Higgin obtained a dark brown 
powder, which he seems to consider as devoid of any tinctorial power. 
A very simple experiment suffices to prove that madder, in its dry state, contains 
very little, if any alizarine ready-formed. If an extract of madder be made with cold 
water, it will be found that the brownish-yellow liquid thus obtained when gradually 
heated will dye as well and as strongly as the madder from which it has been pre- 
pared. Now if the colouring matter were originally present in the form of alizarine, 
this could not take place, since alizarine is almost insoluble in cold water ; and in 
employing it for the purpose of dyeing, it is necessary to dissolve it in warm or boiling 
water before it begins to exert any effect, as is plainly seen in the case of garancine, 
which contains alizarine ready-formed. Nor is there much colouring matter left be- 
hind in the madder after extraction with cold water, for after converting the residue 
in the usual manner into garancine by means of sulphuric acid, it is found to be 
capable of dyeing only very slightly. Nay more, if madder be extracted with hot 
water instead of cold, I have found the residue to give a garancine which dyed darker 
colours than that obtained from the residue of an equal weight of madder extracted 
with cold water, so that it appears that the colour-producing substance is more com- 
pletely removed by cold than by hot water. If an extract of madder with cold water 
be left to stand, there is formed in it, as Mr. Higgin has shown, a flocculent sub- 
stance, while the liquid loses its bitter taste, part of its yellow colour and the whole 
of its power of dyeing, which is now found to reside in its whole extent in the fioc- 
culent substance. This change takes place equally well with or without the access 
of atmospheric air. 
By adding a variety of substances to an extract of madder with cold water, I was 
enabled to ascertain under what circumstances and by what means the tinctorial 
power of the liquid is destroyed, and consequently what is the general character of 
the substance or substances to which it is due. I found that by adding sulphuric or 
muriatic acid to the extract and heating, the liquid, after neutralization of the acid. 
