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



Since this date I have seen a small Calotes seize and eat a small 

 conspicuous orange-red insect, apparently a " lady-bird." 



The behaviour of these reptiles certainly does not appear to 

 afford support to the belief that the butterflies, at any rate, usually con- 

 sidered nauseous, are distasteful to them. 



A Note on the Nature of the Substance formed during fermentation, from 

 which Indigo Blue is eventually formed in Indigo Manufacture ; and on 

 Indigo Brown. — By Surg.-Lt.-Col. G. S. A. Ranking, B.A., M.D., 

 M.R.A.S. 



[Read March, 1896.] 



Indigo liquor when properly fermented is a greenish yellow in- 

 fusion having a very marked greenish fluorescence. In reaction it 

 varies, though the reaction is faintly alkaline when the liquor is most 

 favourably fermented. A distinctly acid reaction always indicates 

 unfavourable fermentation, and results in loss of produce of Indigo-blue. 



It contains a substance in solution which forms a yellow solution 

 with alkalies, and from this yellow solution Indigo-blue may be very 

 readily obtained by simple agitation with air. 



Now the nature of this Indigo-forming substance has been hitherto 

 undecided. That it very closely resembles Indigo-white cannot be 

 denied, as will be seen from a comparison of the reactions of Vat-liquor 

 and solutions of Indigo-white respectively with metallic salts, herein- 

 after set out in tabular form. {See Table page 51.) 



But there are certain difficulties in the way of any theory which 

 would declare them to be identically the same, of which one is this, that 

 Indigo-white is well known to be insoluble except in alkalis, whereas 

 it is certain that in acid Vat-liquor the Indigo-forming body is present 

 in solution. 



For many years I held the opinion that the substance present in 

 the Vat-liquor after fermentation is so nearly allied to Indigo- white as 

 to be practically identical with that body, and I considered that it might 

 be an isomer of Indigo- white, which differed from that body by being 

 soluble in acids, as well as in alkalies ; I have, however, as a result of 

 further research, come to the conclusion that the body present differs 

 from Indigo- white in composition, though in its reactions with metallic 

 salts it is apparently identical, and I have been led to conclude that 

 it is probably Indoxyl (CgHyNO) a body containing one more atom of 

 Hydrogen than does Indigo- white. 



i 



