57 8 SCIENCE PROGRESS 



plant {Indigofera arrecta), and investigated their effect when 

 mixed with pure indigotin and analysed by the method. They 

 found that the indigotin was correctly determined in presence 

 of the first two impurities, but that a special treatment had to 

 be adopted when kaempferol was present. 



As regards the other problem, the determination of the 

 amount of indican in the leaf, the plan that first suggests itself 

 is that of converting the indican into dextrose and indigotin by 

 hydrolysis and oxidation, and then determining the amount of 

 the latter substance ; it has however been found that the full 

 amount of indigotin is not obtained when this is attempted, 

 owing no doubt to the formation of a certain amount of other 

 substances, and thus a determination on these lines gives too 

 low a result. Advantage has been taken by the authors of a 

 suggestion of Beijerinck's, namely, to use the property possessed 

 by indoxyl of combining with isatin to form indirubin ; the 

 solution of indican is boiled with isatin and hydrochloric acid, 

 the acid effects hydrolysis into dextrose and indoxyl, and the 

 latter combines with the isatin to form indirubin, which is 

 filtered off, purified, dried and weighed; air must be excluded 

 during the operation by means of a current of carbon dioxide. 

 The authors found the method satisfactory, and verified its 

 accuracy by experiments with pure indican. 

 • Now that it is possible to examine the leaves and the 

 products in the various stages of manufacture with much 

 greater accuracy than was previously the case, there is hope 

 that great improvements can be made both in growing the 

 plant and obtaining from it a much better yield of indigotin. 

 To give an instance of this : the action that goes on in the 

 steeping process seems to be the conversion of the indican into 

 dextrose and indoxyl by the action of an enzyme present in the 

 leaves ; in some experiments of the authors this enzyme was 

 used to decompose indican, and indigotin was then obtained by 

 oxidising with air, thus imitating the present practice, and it 

 was found that at the best only 68 per cent, of the full yield of 

 indigotin was obtained. This and other evidence point to the 

 present process of manufacture being one of no great efficiency ; 

 and it is to be hoped that the Government will aid the con- 

 tinuance of the present researches and give the indigo-growing 

 industry every chance of holding its ground against the com- 

 petition of the artificial product. 



