1 62 Mr. Charles O'Neill 



On the action of Acetic Acid, with oxidising sub- 

 stances, on Indigo Blue. By Charles O'Neill, F.C.S. 



{Received May 18th, i8g2.) 



If a quantity of very pure indigo blue in fine powder be 

 placed in a glass or porcelain mortar, with 20 or 30 times 

 its weight of mono-hydrated or glacial acetic acid, well 

 mixed up, then crystals of permanganate of potash added 

 in small portions, at intervals of a few minutes, with con- 

 tinual stirring and grinding, it will be found that chemical 

 action is taking place, heat is evolved, the mixture thickens 

 almost to a paste, and when the quantity of permanganate 

 added is equal to about one-fourth part of the weight of 

 indigo operated upon, the operation is finished. Examined 

 under a pretty high power of the microscope, say with 

 yi inch objective, the contents of the mortar are found to 

 consist of a mass of small prismatic crystals floating in a 

 nearly colourless liquid ; the crystals have a faintly yellow 

 colour, and no indigo blue is visible. The thick mass of 

 crystals may be drained on a filter, washed with strong 

 acetic acid and then with water, until all soluble matters 

 are removed, then dried very gradually in a warm place, 

 where the temperature for the first few hours should not 

 exceed 20 to 25 C. ; after most of the water has evapo- 

 rated, the temperature may be gradually increased up to 

 ioo° C, at which heat the dry product is permanent, and 

 may be kept for years unchanged in a dry place. 



Other oxidising agents may be used, but the only ones 

 to be recommended are the di-oxide of lead, the red oxide 

 of lead, either added directly or previously dissolved in 

 strong acetic acid, and lastly, the higher oxides of manganese 

 lower than the di-oxide. The two lead oxides act perfectly 



