FORMATION OF INDIGO-BLUE. 1 87 



liquid a yellow precipitate fell, and on again filtering the 

 liquid ran through almost colourless. The lead precipitate 

 being decomposed with dilute sulphuric acid, the filtered acid 

 liquid was boiled, when it gave a few black flocks, which, 

 however, contained no indigo-blue.* If, however, sulphuric 

 or muriatic acid in excess were added to the liquid filtered 

 from the lead precipitate, the liquid soon became green and 

 began to deposit indigo-blue even before it could be filtered 

 from the sulphate or chloride of lead, and after filtration and 

 boiling it yielded flocks containing an abundance of the 

 colouring matter. If acetate of lead was added to an extract 

 of woad leaves made either with hot or cold water, if the 

 precipitate thereby produced was separated by filtration and 

 ammonia was added to the filtrate, a pale yellow precipitate 

 fell. This precipitate having been decomposed with sul- 

 phuric acid, the filtered acid liquid gave on boiling flocks 

 containing indigo-blue, while the flocks obtained in a similar 

 manner by boiling with acid, the liquid filtered from this pre- 

 cipitate gave no indigo-blue. If this lead precipitate was 

 treated with a cold concentrated solution of carbonate of 

 soda, a yellow solution was obtained, which on being tried 

 as before with sulphuric acid afforded no indigo-blue, whilst 

 the precipitate on being treated with acid gave indigo-blue as 

 before. But if the lead precipitate was suspended in water 

 and a current of carbonic acid gas was passed for some time 

 through the liquid, it was completely decomposed, its colour 

 changed from yellow to white, and it now consisted almost 

 entirely of carbonate of lead, whilst the liquid had acquired 

 a yellowish colour, and on being boiled with acid deposited a 

 quantity of blue flocks, which consisted of indigo-blue in a 

 state of great purity, as they dissolved in boiling alcohol 

 with a beautiful blue colour, the alcohol depositing on cool- 

 ing crystalline scales, which were blue by transmitted, and 



* If the acetate of lead is in the least degree contaminated with basic acetate, 

 it will he fonnd to precipitate some of the indigo-producing bodj. 



