166 Mr. Charles O'Neill on 



propose to consider four or five of those which can be 

 followed most easily ; and, to trace the changes which take 

 place, will assume a structure for the body which has no 

 other pretensions than as forming a sort of working hypo- 

 thesis to illustrate the changes. The supposed structure is as 

 follows : — 



UoH 16 W 2 U 6 - c 8 H 5 NO/ U \C 2 H 3 0/ U - 



I am not going to attempt defending this arrangement as a 

 rational arrangement. I know nothing about the constitu- 

 tion of the body, I have never read about any similar body, 

 and that acetic anhydride should exist in it seems very 

 improbable. 



Decomposition by steaming and boiling with water. The 

 addition of the elements of water to the oxy-aceto-indigotin, 

 which is effected by boiling it in water or steaming it, splits 

 it up and produces two molecules of acetic acid, one of 

 isatin, and half a molecule of indigo blue. The calculated 

 percentage is acetic acid (mono-hydrated) 31 "6, isatin 345, 

 and indigo blue 387, making 104/8 ; these quantities have 

 been obtained many times ; the percentage of acetic acid 

 is very regular, but the percentage of indigo and isatin are 

 subject to a perturbation not yet clearly understood ; not in 

 every case, but in most cases, there is production of a small 

 quantity of a fourth substance, very little soluble in water, 

 but easily soluble in chloroform, from which it separates in 

 lustrous yellow or golden coloured crystals. It is apparently 

 the same substance which is formed by the direct oxidation 

 of indigo in air, it has not been obtained in sufficient 

 quantity to be examined ; it may amount to as much as 8 

 or \o°/ of the weight of aceto product, but generally much 

 less. It is believed to result from the interaction of indigo 

 and isatin at the moment of their formation, and to be a 

 substance intermediate in composition between indigo and 

 isatin. The length of time required to split up the aceto 



