1896.] G. S. A. Ranking — A Note on Indigo Manufacture. 49 



There are only two substances known to chemists which yield Indigo- 

 blue on agitation of their solutions with air. These ai?e : — 



(a) Indigo-white (CgHgNO) soluble in alkalis to yellow solution, 

 playing the part of a weak acid. 



(6) Indoxyl (CyHyNO) soluble in acids or alkalis, and its solution 

 in hot water showing a yellowish green fluorescence. 



" It is simultaneously an acid and a base : its alkaline solution 

 absorbs Oxygen from the air with formation of Indigo-blue : which is 

 also formed when ferric chloride is added to its hydrochloric acid 

 solution." * Now it requires very little further enquiry, before we are 

 struck with the similarity of the physical characters of this body and 

 those of the body existing iii Indigo Vat-liquor after fermentation. 

 When we look a little further, and enquire into the chemical behaviour 

 of Indoxyl, we find that it contains two atoms of replaceable Hy- 

 drogen. It forms derivatives in which one of these atoms is displaced, 

 thus Ethyl-Indoxyl CgHgNO (C3H5) is Indoxyl in which one atom of 

 Hydrogen is replaced by Ethyl : graphically — 



OH OC2H5 



" L L 



CfiH / ^'CH CfiH,/ A OH 



\NH-^ ^NH -^ 



Indoxyl Ethyl-Indoxyl. 



Prom this we may infer that a Potass-Indoxyl (OgHgNOK) Sod- 

 Indoxyl (CgHgNO Na). Ammon Indoxyl (CgHgNO Am) are theoret- 

 ically possible. We may also notice that if we simply remove this 

 atom of Hydrogen we should convert Indoxyl into Indigo-white, thus 



Indoxyl Indigo-white. 



= 2 0gH,<;^g>CH-t-H2O 



and this indicates that the above would represent the graphic formula 

 of Indigo-white. Further oxidation would give us Indigo-blue, the 

 atom of Hydrogen contained in the CH group being removed: thus f 



2CaH.<S>CH + 



Indigo-white 



Indigo-blue. 



* Roscoe and Schorlemmer, Vol. Til. p. 40. 

 t R. and S., Vol. III. page 42. 

 J. II. 7 



