Dr. Schunck on the Formation of Indigo-blue. 87 



ever, it yields other products, which are always the same at every 

 subsequent stage of the process. If the watery solution be then 

 boiled with the addition of sulphuric or muriatic acid, it becomes 

 in the first instance of a darker colour, and after considerable 

 boiling, deposits slowly a quantity of dark brown, almost black 

 flocks. The liquid filtered from these flocks contains sugar, just 

 as in the case of indican itself. The flocks themselves generally 

 consist of two bodies. If they be collected on a filter, washed 

 with water, and then treated with boiling alcohol, a part dissolves 

 with a brown colour, and after filtration and evaporation, is left 

 as a dark browm, shining, resinous substance. This substance 

 melts in boiling water into brown coherent masses. It is com- 

 pletely dissolved and decomposed by boiling nitric acid. It 

 dissolves in ammonia with a brown colour, and the solution 

 gives brown precipitates with the chlorides of bai'ium and cal- 

 cium. It is completely precipitated from its alcoholic solution 

 by sugar of lead, the precipitate being brown. I propose to call 

 this body Indiretine. That portion of the dark brown flocks 

 which is insoluble in boiling alcohol, dissolves in caustic alkahes 

 with a dark brown colour, and is precipitated by acids in black 

 flocks. As it bears some resemblance in its outward properties 

 to humus, I shall call it Iiidihumine. 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 temperature be raised to a certain 

 degree, which proves that oxygen plays no part in the process. 

 It is apparently efiiected instantly when indican comes into con- 

 tact 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 ex- 

 posed 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 colouring matters ; 

 and it goes far to prove that indigo-blue docs not pre-exist in 

 indican even as a copula, but is merely contained in it poten- 

 tially. 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 



