Chemical Science. 153 



but in close vessels a quantity of charcoal is deposited. Vo- 

 latile and fixed oils dissolve small portions of it. 



Being analyzed by oxide of copper, its composition appeared 



1 atom azote ... 1.75 .. • 10-77 



2 oxygen . . 2.00 . . • 12.31 



4 hydrogen . . 0.50 . . • 3.08 



16 carbon . . 12£0 . . • T^f 



16.25 100 



Excepting a minute proportion of lime, precipitated indigo 

 gave the same result. 



When indigo is digested in sulphuric acid, it is con- 

 verted into a very peculiar blue substance, to which Mr. Crura 

 has oiven the name of cerulin. The mixture requires much 

 wate°r to dissolve it, and its filtered solution is precipitated by 

 potash. This precipitate is as plentiful before one-fourth of 

 the acid is saturated as when the whole is neutralized ; it is 

 also produced by sulphate of potash. When thrown on a 

 filter and washed, it entirely dissolved in pure water, but the 

 presence of any salt of potash rendered it insoluble. 



Some of the precipitate, washed first by weak solution of 

 acetate of potash, and afterwards by alcohol, was burnt in a 

 crucible; a large quantity of ashes was left, consisting of neutral 

 sulphate of potash, with a little iron. Another portion of the 

 substance, prepared even with muriatic acid and muriate o^ 

 potash, gave sulphate of potash as before. Hence it appears 

 to be a combination of cerulin with sulphate of potash, and 

 may be called ceruleo-sulphate of potash. The salt forms more 

 than a fourth of its weight. 



A ceruleo-sulphate of soda may also be formed ; it is more 

 soluble than the compound with potash. Ceruleo-sulphate of 

 ammonia is still more soluble, and is decomposed by potash or 

 soda. The compound with barytes is extremely insoluble. 

 An abundant blue precipitate is formed by muriate of barytes 

 in solutions of ceruleo-sulphate of potash, containing so little 

 sulphuric acid as not to be troubled in the slightest degree, if 

 the cerulin be previously destroyed by nitric acid. 



Ceruleo-sulphate of potash when moistened is almost black, 

 when dry of a deep copper-colour— one part dissolves in 140 

 of water, forming an intense blue solution, which is precipitated 

 by every thing but distilled water. Luminous objects seen 

 through it appear of a rich scarlet-colour, but a single drop of 



