1S96.] 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 are : — 



(a) Indigo- white (C 8 H 6 NO) soluble in alkalis to yellow solution, 

 playing the part of a weak acid. 



(&) Indoxyl (C 8 H 7 NO) 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 in 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 C 8 H 6 NO (C 3 H 5 ) is Indoxyl in which one atom of 

 Hydrogen is replaced by Ethyl : graphically — 



OH O0 2 H 5 



cL L 



C 6 H 4 <f ^CH 6 H 4 / \° H 



Indoxyl Ethyl-Indoxyl. 



From this we may infer that a Potass-Indoxyl (0 8 H 6 NOK) Sod- 

 Indoxyl (C s H 6 NO Na). Ammon Indoxyl (C 8 H 6 NO 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. 



= 2C 6 H 4 .<£° I >CH+H 2 



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 



2C 6 H 4 <£°>CH + 



Indigo-white 



= 2C 6 H 4 <£° I >C + H 2 

 Indigo-blue. 



* Roscoe and Schorleinmer, Vol. III. p. 40. 

 f R. and S., Vol. HI. page 42. 

 J. II. 7 



