1896.] G. S. A. Ranking — A Note on Indigo Manufacture. 55 



used to macerate the Indigo plant, the application of heat during 

 maceration (" steeping "), and last but not least prolonged " beating " 

 in order to oxidise imperfectly fermented Vat-liquor, all result in the 

 formation of the soluble Indigo-brown and should therefore be avoided 

 in manufacture. 



The gases evolved during fermentation I have found to be principal- 

 ly Carbon dioxide and Nitrogen in the following proportions 002 = 31 

 per cent. N = 62 per cent. Hydrogen forms a very small proportion of 

 the evolved gases, only 6*75 per cent. 



Marsh gas also seems to be very sparingly generated during fer- 

 mentation of Indigo. I propose to extend my observations on the 

 evolved gases at some future opportunity. 



