FORMATION OF INDIGO-BLUE. 197 



Indihumine, Its similarity to the indigo-brown of Berzelius 

 is so great, as almost to lead me to suspect that it is the 

 same body. Whether this is the case or not, can only be 

 ascertained by analysis. Sometimes the brown substance 

 formed by the action of acids on modified indican is entirely 

 soluble in boiling alcohol and contains no indihumine, but 

 under what conditions this takes place, I am unable to say. 

 The change which indican undergoes during this process 

 consists merely in its absorbing the elements of water. It 

 proceeds in vacuo as well as in the air, provided the tem- 

 perature be raised to a certain degree, which proves that 

 oxygen plays no part in the process. It is apparently 

 effected instantly when indican comes into contact with 

 alkalies in its watery solution, though the alcoholic solution 

 may be made alkaline, with ammonia at least, without any 

 alteration taking place. It is certainly a most remarkable 

 circumstance, that by merely taking up the elements of water 

 indican should be converted into a substance, which when 

 exposed to the action of acids yields no longer indigo-blue 

 and its allied red colouring matter, but bodies of an entirely 

 distinct nature which have none of the properties of colour- 

 ing matters, and it goes far to prove that indigo-blue does 

 not pre-exist in indican even as a copula, but is merely con- 

 tained in it potentially. That the view I have taken of this 

 metamorphosis is the correct one, is proved by a singular 

 observation which I once accidentally made. Having on 

 one occasion obtained a dilute solution of indican, I tried a 

 small quantity of it by boiling with sulphuric acid, and 

 ascertained that it gave indigo-blue and indirubine. But on 

 heating the whole quantity to the boiling point with acid, I 

 obtained instead of these two bodies a substance dissolving 

 in alcohol with a brown colour. It was evident that the 

 indican, in consequence probably of the solution being very 

 dilute, had taken up the elements of water before the acid 



