80. Dr. Schuuck on the Formation of Indigo-blue. 



adding to it sulphuric or muriatic acid and boiling, it became of 

 a darker colour, and deposited a quantity of dark brown, almost 

 black flocks. Now these flocks contained indigo-bluc ; for if 

 after collecting them on a filter and washing out the acid, they 

 were treated with boiling alcohol, they communicated to the 

 latter a bright blue colour ; and on being treated with a boiling 

 alkaline solution of protoxide of tin, they gave a yellow solution, 

 which on exposure to the air became covered with a thin blue 

 film. A small quantity of finely-chopped woad leaves having 

 been pounded in a mortar with water until converted into a 

 uniform green pulp, yielded on being strained through calico a 

 dark green opake liquor. On heating this liquor to near the 

 boiling-point, the vegetable albumen contained in it coagulated, 

 cal^ying down with it the green colouring matter. On now 

 filtering through paper, a green coagulum was left on the filter, 

 while a clear light yellow liquid ran througli. On adding acetate 

 of lead to the liquid, a yellow precipitate fell ; and on again filter- 

 ing, the liquid ran through almost colourless. The lead preci- 

 pitate being decomposed with dilute sulphuric acid, the filtered 

 acid liquid was boiled, when it gave a i&w 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 sul- 

 phate 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 sepa- 

 rated by filtration and ammonia was added to the filtrate, a pale 

 yellow precipitate fell. This precipitate having been decomposed 

 with sulphuric 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 preci- 

 pitate gave no indigo-blue. If this lead precipitate was treated 

 with a cold concentrated solution of carbonate of soda, a yellow 

 solution was obtained, Mhich on being tried, as before, with sul- 

 phuric acid, afforded no indigo-blue ; whilst the precipitate, on 

 being treated with acid, gave indigo-bluc as before. But if the 

 lead precipitate was suspended in water, and a current of car- 

 bonic 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 coKour, and on being 

 boiled with acid, deposited a quantity of blue flocks, which con- 



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

 acetate, it will be fouud to precipitate some of the judigo-producing body. 



