EXPERIMENTS ON INDIGO. gjj 



colour, which acids change to a green by saturating the al- 

 kali. When the solutions are concentrated, the green mat- 

 ter falls down in green flocks. Alcohol dissolves this pre- 

 cipitate, and forms a red tincture ; but this, when spread 

 out thin, or mixed with water, appears green, as it does when 

 viewed on its surface. 



c. Alcohol being added to the concentrated liquor b, from 

 which the green matter had been precipitated, separated a 

 substance, the taste of which was slightly bitter and astrin- 

 gent, and which burnt on the coals, diffusing a smell of 

 empyreumalic vinegar. The alcohol acquired a reddish 

 colour, owing to the combination of green matter with am- 

 monia. 



Thus the substances separated from the indigo by water 

 were, 1, ammonia: 2, indigo at a miuimum of oxidation : 

 3, a green matter : 4, a slightly bitter and astringent matter, 

 of a yellowish brown colour. Of these the 2d and 3d are 

 held in solution by the ammonia. 



100 parts of indigo lost 12 by treatment with water. 



Art. II. From the indigo exhausted by water alcohol Action of 

 took up, 1, some green matter: 2, a matter that I call red a!coho '- 

 resin : 3, indigo at a maximum of oxidation. 



The insolubility of the green matter in the treatment with 

 water [Art. I.) I ascribe to the want of a sufficient quantity 

 of ammonia to dissolve it entirely, and the affinity of the red 

 matter for it. 



The principal difference between the red resin and the 

 green matter is, that the latter is rendered red by alkalis, 

 and that this compound becomes greeu by the addition of 

 an acid ; while the colour of the former is not changed either 

 by acids or alkalis, only acids produce with it a red floecu- 

 lent precipitate. 



lu acting twice on the indigo alcohol took up 26 parts 

 from the 88 left by the water. I Suffered the alcohol to act 

 on it no longer, when it began to acquire a viclet tint. 



Art. III. Muriatic acid dissolved. 10 parts ; 2 of which Action of ir,u- 

 were iron mixed with aluuiine, 2 carbonate of lime, and g n ~ tlc ac ^* 

 probably red matter, that was dissolved in the acid after be- 

 ing decomposed. 



The preceding experiment having shown, that the indigo p jrt v er act : cr , 



„..,„ of aicolioi. 



