72 
in this process might in reality be due to the presence of one 
or both of these acids rather than to the sugar itself. This 
supposition was completely verified by experiment. The 
colouring matter disappeared quite as rapidly when acetate 
or formiate of soda was employed in the place of grape sugar. 
The use of the latter was therefore abandoned in the subse- 
quent experiments. In the present communication the 
author confines himself to an account of the combined action 
of alcohol, acetate of soda, and caustic soda on indigo blue. 
The process adopted was quite simple. Pure indigo blue 
was introduced into a large quantity of ordinary spirits of 
wine, and, after being well agitated, the mixture was raised 
to the boiling point. A quantity of pure acetate of soda, 
previously deprived of its water of crystallization, and a 
little caustic soda were then added, and the boiling was 
continued for several hours, A reduction of the indigo blue 
took place in the first instance, as was evident from the deep 
red colour of the liquid. On agitating with air this red 
colour disappeared for a moment, the indigo blue being pre- 
cipitated in powder, but after some time the liquid acquired 
a dark brown colour and deposited nothing on exposure or 
agitation. The process was then completed. In order to 
obtain the products formed, the brown liquid was evaporated, 
and, when the evaporation was nearly completed, water and 
an excess of sulphuric acid were added, which threw down a 
brown insoluble mass, consisting partly of resinous, partly of 
pulverulent substances. From the liquid, which was of a 
light brown colour, a crystallized acid was obtained, which 
after being purified was found to consist of anthranilic 
