164 Mr. Charles O'Neill on 



vat is very suitable for these experiments, but such a 

 precipitate made from commercial indigo is never pure 

 indigo blue ; very good specimens may shew 92 % indigo 

 blue, hardly ever a higher percentage. The nearest 

 approach to pure indigo blue suitable for the treatment 

 described is obtained by the reduction of pure crystalline 

 indigotine, obtained by sublimation, or better by solution 

 from boiling aniline. Such a product may contain 99^ 

 indigo blue, and will give nearly the calculated quantitative 

 results in these experiments. It would have been very 

 desirable to act at once upon the pure indigo blue from 

 aniline, but its crystalline condition impedes the complete 

 action of the acids and oxidising agents ; with the calcu- 

 lated amount of oxidising matters only a small portion of 

 the crystalline indigotine is acted upon. If the quantity of 

 permanganate be increased to eight or ten times the calcu- 

 lated quantity, the crystals are finally acted upon, although 

 not completely, with evolution of heat. The solution in 

 which the action takes place is a saturated solution of 

 higher oxides of manganese, secondary reactions have taken 

 place, the yield is much smaller than with the amorphous 

 or very finely crystalline precipitated indigo, and it does not 

 shew quite the same results. 



The product made, as described, from precipitated 

 indigo, viewed in bulk has a greyish, greenish, or blueish 

 colour ; in thin layers it is nearly white, with a yellow 

 tinge ; it is no doubt either white or a very pale yellow ; 

 the various shades that various preparations shew are 

 owing to the presence of small quantities of indigo blue 

 unacted upon. In the method of preparation it will have 

 been observed that two practically insoluble bodies are 

 used to produce a third insoluble body. It is curious how 

 this third body should assume the crystalline form, but it 

 does so, and envelopes a portion of blue in the crystals 

 which cannot be reached by the agents employed, unless 



