The Action of Acetic Acid on Indigo Blue. 169 



and, upon cooling, bright yellow crystals are deposited. 

 It is difficult to separate these crystals from the indigo 

 in a pure state, and I have had recourse to the device 

 of taking the mixture of yellow crystals and destroying 

 the indigo with a mixture of permanganate and dilute 

 sulphuric acid, which has no action upon the yellow crystals. 

 Combustion gives a ratio of C to H as 16 : 7, or a little 

 under ; no doubt the H found in this is more than should 

 be, and I consider that the formula will be C 8 H 3 NO, or a 

 multiple of it. The reaction producing these two bodies, 

 indigo and the yellow crystals, is probably quite internal 

 to the molecule of the oxy-aceto-indigotin body, and merely 

 a re-arrangement of its elements under the constraining 

 influence of heat in a medium non-hydrating, as 



{c.i:S8} ° {cSo}° = 2 < c = h <°°> + c « h « n ° + c - h ' no - 



The oxidised indigo nucleus is supposed to lose its attached 

 oxygen and two of hydrogen from one of the half molecules, 

 which form water and convert the acetyl rest into two of acetic 

 acid. This yellow body has not been closely examined. 



