.214 EXPERIMENTS OS XNDtGtf. 



Was not completely divested of foreign colouring matter, I 

 treated it again with alcohol, till this liquid became blue. 

 By this treatment it lost 4 parts of red resin, mixed with a 

 little indigo. 



In these different processes the indigo lost 0*52 of foreign 

 matter, which reduced it to 0*48, from which 0*03 more 

 must be deducted for the silex it still contains. 



Indigoes differ. Every sort of indigo does not yield the same results on 

 analysing as, that of Guatimala, on which I operated. In 

 most the green matter changed ta a fawn colour ; it became 

 very red on the addition of alkalis; but acids did not render 

 this compound green. One specimen, in pretty thick 

 square cakes, of a black blue colour, yielded me no indigo 

 at a minimum. Its ashes contained more iron than that of 

 Guatimala, and also magnesia. Some indigo, which I was 

 informed came from Bengal, yielded me a twentieth of in- 

 digo at a minimum; and its ashes contained a little sul- 

 phate of lime. In some indigoes I found traces of phosphate 

 of lime. 



Green matter It is not very common to find the green matter in full 

 possession of its properties : sometimes yellow extractive 

 matter is so predominant, that it is difficult to detect it; 

 and sometimes no vestige of it is to be found. In general I 

 remarked, that those indigoes, which contained most am- 

 monia, contained also more indigo at a minimum, and more 

 green matter, than others. The indigo cf Java afforded me 

 the last in its greatest purity. 



Colouring I consider the colouring matters accompanying indigo as 



™ a o^flpj 0118 " or, g' na ting from the same substance variously modified. 



Purple smoke Sect. III. The source of the purple smoke was now easily 

 detected. On heating successively the green matter, ex- 

 tract, and gum, extracted by water, and the red resin ex- 

 tracted by alcohol, no purple smoke was perceivable. But 

 trying the same experiment on the indigo separated, by 

 water, on that separated by alcohol, and lastly on that 

 treated successively by water, alcohol, and muriatic acid, a 

 fine purple smoke arose, much deeper coloured than that 

 produced by an equal quantity of indigo not purified. 



th<? nure in- This smoke is not the result of a decomposition of the 



«ligo sublimed. j u( jjg by heat : for we found by experiment, that it was 



this 



