1896.] G. S. A. Ranking — A Note on Indigo Manufacture. 



51 



white are the same, the only difFerence being in the proportions of the 

 reagents required : * and this would explain how it is that the Indigo 

 Vat-liquor while giving the reactions of Indigo-white with alkalis and 

 metals, still may have an acid reaction originally, if the body present is 

 Indoxyl CgH^NO^or »|/ Indoxyl. Which we might call an acid Indigo- 

 white on the analogy of the acid carbonates. 



Having regard to the fact that CO3 is largely present during Indigo 

 fermentation it is not improbable that at some stage Indoxylic acid 



^6^4 ^v^N'H^ CH.COg.H 



is present, but as this, by the splitting off of GOg, yields Indoxyl, and in 

 alkaline solution behaves just as does Indoxyl, yielding Indigo- blue by 

 oxidation, this does not in any way ajffect the foregoing explanation of 

 the reactions occurring during the manufacturing process. 



The following table shews the reactions above referred to. 



Table shewing comparison of reactions of Indigo Vat-liquor after 

 due fermentation, with those of Reduced or white Indigo. 



The reactions of Reduced Indigo vide 



Watts Dicty. of Chemistry, ed. 1865, 



Vol. III. 



Reactions of fermented Indigo liquor 

 with the reagents mentioned. 



Result. 



Earth metals and heavy metals give a 

 white ppt. turning blue in air. 



Magnesium compound is partly soluble, 

 partly white ppt. turning blue, partly 

 a yellow solution. 



Aluminium compound white, but rapidly 

 turns blue in the filter. 



Manganous compound dirty green, yields 

 no sublimate of Indigo-blue. 



Zinc compound is white, rapidly blue in 

 air and then yields a sublimate of In- 

 digo-blue when heated. 



Lead compound white and slightly crys- 

 talline, turns rapidly blue on exposure 

 to air, if then heated it detonates 

 slightly and yields reduced lead. 



Ferrous compound is white, quickly blue 

 on exposure to air : if then heated, 

 yields no sublimate of Indigo-blue. 



White ppt. becoming dark blue 



in air. 

 White ppt. becoming blue in air. 

 Filtrate yellow. 



White ppt. becoming blue rapid- 



ly- 



Bluish green ppt. 



No sublimate on heating. 



White ppt. becoming rapidly 

 blue. 



No sublimate obtained. 



White ppt. inclining to green, 

 blue on exposure to air, on 

 heating deflagrates yielding 

 Pb. 



Whitish green ppt., passing 

 through green to blue (also 

 some ferric hydrate ppt. owing 

 to impurity of ferrous salt.) 



* In the case of Indigo-white we should have the following reactions : 



(a) 2 C8H6NO-1-2 K0H = 2 CgHaNO.K.K. (alkaline solution) +2 HjO. 



(b) As in case of Indoxyl-Barium compound. 



