$40 Fads upon which to found a History 



If wc pivt pure ammonia upon carbonate of cobak in ex- 

 cess, this alters the ease eompletely. The carbonate of' co- 

 balt is divided into two parts : the one yields its acid to the 

 ammonia and becomes hydrate, which is precipitated to the 

 bottom of the vessel, while the portion not decomposed is 

 dissolved into alkaline carbonate. 



Here we have already two kinds of ammoniaca) solutions 

 of cobalt. There is a third discovered by Tassaert, but in 

 general very little remarked hitherto. We obtain it by put- 

 ting hydrate well washed, or blue oxide, into a flask full of 

 ammonia and well closed. The solution is made in 24 

 hours. It is red like the former; but differs from them in 

 this respect, that if we pour a drop of it into boiling water, 

 blue oxide is immediately precipitated ; when we operate 

 with cold water we obtain green oxide. If ammonia dis- 

 solves the hydrate of cobalt, or the fresh blue oxide, more 

 easily than the gray oxide, it is because the two former are 

 in very minute division. 



Distillation of the arnmoniacal Solution. — When we distil 

 the solution of carbonated cobalt, carbonate of ammonia 

 passes over ; the liquor in the end deposits an oxide at first 

 of a dirty green, but which afterwards becomes black. This 

 is a mixture of gray oxide and black oxide. 



How happens this byper*oxidation ? M. Proust merely 

 states the fact, and abstains from explanation where data 

 are wanting. 



Hydrate of Cobalt, — The crystals of sulphate, or of ni- 

 trate, thrown into a flask full of liquid potash, and im- 

 mediately closed, are there decomposed : a blue precipitate 

 is formed, which passes to the violet, afterwards to the red_, 

 by becoming hydrate. 



If we boil hydrate with potash, the latter dissolves oxide, 

 and is tinged with a fine blue colour. This solution is de- 

 composed upon the addition of water. In the air the oxide 

 becomes black, and is deposited. 



The hydrate is dissolved cold in the cafbonate of potash, 

 and tinges it red. The oxide is not dissolved. 



The hydrate of cobalt is of the colour of a dead rose leaf: 

 Ihe acids dissolve it with heat, and without effervescence. 



The hydrate is not decomposed by ebullition, either in 



pure 



