296 Dr. Schunck on some Products 



to the boiling-point. A quantity of pure acetate of soda, 

 previously deprived of its water of crystallization, and a little 

 solid caustic soda were then added, and the boiling was con- 

 tinued for several hours. A reduction of a portion 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 precipitated in powder, to be again dissolved on boil- 

 ing the liquid • but after some time the liquid acquired a 

 dark-brown colour, and deposited nothing on exposure or 

 agitation. The process was then completed. There some- 

 times remained a residue of indigo-blue, which obstinately 

 resisted the action of the boiling liquid ; but, on pouring off 

 the latter, and adding fresh materials, it generally disappeared 

 rapidly. I found it advisable to employ only a small quan- 

 tity of indigo-blue at a time, as the process is a slow one 

 and requires a great excess of alcohol and acetate of soda. 

 The presence of caustic alkali I found to be quite essential, as 

 no perceptible action took place without it ; but the quan- 

 tity required was not large. The stronger the alcohol, and, 

 generally speaking, the freer from water all the substances 

 employed were, the more rapidly was the process completed. 



In order to obtain the products resulting from this pro- 

 cess, I proceeded as follows : — The dark-brown alcoholic liquid 

 containing them was first mixed with sulphuric acid until it 

 had acquired a slightly acid reaction, and it was then evapo- 

 rated. During evaporation, brown resinous masses were 

 deposited ; and on adding water when the evaporation was 

 nearly completed, a fresh quantity of resin-like matter was 

 thrown down. The liquid filtered from this matter was still 

 brown. It was evaporated to a syrup, which, after standing 

 some time, became solid from the formation of crystals, con- 

 sisting chiefly of acetate of soda. The whole mass of crystals 

 was then dissolved in boiling alcohol, and tolerably strong 

 sulphuric acid was added to the solution, until no more sul- 

 phate of soda was precipitated, care being taken to avoid an 

 excess of the acid. The liquid, after standing some time, was 

 filtered and evaporated, so as to drive off the acetic acid as 

 well as the alcohol. When the evaporation was nearly com- 

 pleted, water was added, which threw down a large quantity 

 of a brown pulverulent substance, as well as a little brown 

 resin, which, after filtration, were added to the resinous 

 matter previously obtained. The filtered liquid had lost much 

 of its brown colour. I shall return to it presently. 



The products insoluble in water obtained in this manner 

 consist partly of resinous, partly of pulverulent substances. 



