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



substance contained in madder capable of dyeing, the xanthine 

 must, daring 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 decom- 

 position of the xanthine is caused by the action of a peculiar 

 ferment contained in madder, and which is extracted together 

 with xanthine 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 prepared. Now if the colouring matter were origin- 

 ally present in the form of alizarine, this could not take place, 

 since alizarine is almost insoluble in cold water; and in em- 

 ploying 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 behind 

 in the madder after extraction with cold water, for after con- 

 verting 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 substance, 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 flocculent substance. This change takes place 

 equally well with or without the access of atmospheric air. 



I3y adding a variety of substances to an extract of madder 



