■52 



G-. S. A. Ranking — A Note on Indigo Manufacture. [No. 1, 



The reactions of Reduced Indigo vide 



Watts Dicty. of Chemistry, ed. 1865, 



Vol. III. 



Eeactions of fermented Indigo liquor 

 with the reagents mentioned. 



Reagent. 



Result. 



Cobalt compound grass green yields no 

 sublimate of Indigo-blue. 



Nitrate of silver produces in aqueous so- 

 lution of the potassium compound a 

 ppt. -which is at first transparent brown 

 and then becomes black ; it is not 

 acted upon by the air, but when heated 

 produces a gentle explosion and yields 

 a sublimate of Indigo-blue, and a resi- 

 due of metallic silver. 



CoCl 2 

 AgN0 3 



Grass green ppt. becoming dark 

 bluish green, yields no subli- 

 mate of Indigo-blue. 



Brown ppt. becoming black 

 glossy looking not altered in 

 air : when heated after drying 

 detonated slightly* yielding 

 sublimate of Indigo-blue. 



Residue metallic silver or oxide 

 of silver : not sol. in NH 4 HO — 

 Sol. in HNO 3 repptd. by HC1 



.'. Ag. 



N.B. — All the above reactions were obtained in Vat-liquor rendered 

 distinctly alkaline with KOH dilute, with which a yellow solution was 

 formed rapidly oxidising with formation of Indigo-blue. 



It is therefore necessary to add the alkali to each portion of the 

 Vat-liquor separately to get trustworthy results. The similarity of the 

 reactions of fermented Indigo-liquor and of a solution of reduced Indigo 

 is seen in the above series. The italics in the third column shew the 

 only points of difference observed. 



A few more remarks upon the above precipitates obtained from 

 fermented Indigo Vat-liquor will be of interest. All the precipitates 

 enumerated in the above Table, with one exception, when dried at 100°C 

 and treated in a porcelain capsule with strong HgSO^ yield a dark 

 green solution, which upon the addition of water deposits Indigo -blue, 

 the filtrate in the case of the soluble sulphates giving the character- 

 istic reactions of the metallic base used as a precipitant. 



There is, however, one noticeable exception to this rule in the case 

 of the Sodium-silver-indigo compound, which does hot detonate on heat- 

 ing and yields a sublimate of a "brown colour, not of Indigo-blue — on 

 treatment with concentrated H 2 SC>4 it turns brown and yields no In- 

 digo-blue on the addition of water. I have thought it interesting to 

 examine the composition of this salt, and have arrived at the conclusion 

 that the Indigo in it is not Indigo-blue, but one of the other compounds, 



* Absence of CO q H proved. 



