of Cobalt and Nickel. 34 1 



pure water or in alkalized water. It loses from 20 to 21 of 

 water by heat, and is reduced to very pure gray oxide. 



It keeps very badly under water : when it is in contact 

 with the air it becomes black. The dry hydrate is better 

 preserved, but attracts carbonic acid. 



When we throw crystals of sulphate into a flask full of 

 ammonia and immediately closed, they give a blue preeipi- ^ 

 tate, which d(K?s not become red a« in the potash. M. Proust 

 asserts that the hydrate is formed, but that it is dissolved 

 in some proportion in ammonia ; so that it is the hydrate 

 which colours the solution, and not the simple oxide. 



Valuation of the Oxygen in the minor Oxide. — 100 parts of 

 gray oxide, reduced with proper precautions in a closed 

 crucible, give 63| of metallic grains. The quintal of cobalt 

 seems therefore to absorb 19 of oxygen, in order to become 

 minor oxide. 



Major oxide. — If we distil a nitric solution of cobaU, 

 black crusts are deposited upon the sides of the retort, ni- 

 trous gas is disengaged, and we obtain from 1 25 to 1 26 of 

 black oxide as the residue. Hence we may conclude, thai 

 the maximum of ihe oxidation of the cobalt exists about 25 

 or 26 in 100. 



This oxide is not dissolved in the nitric and sulphuric 

 acids, except by losing the portion of oxygen which consti- 

 tuted its maximum. 



It gives oxygen gas with the mtlriatic acid. 

 it is inso-luble in ammonia and potash. 

 The black oxide, heated for half an hour at the bottom 

 Df a crucible, again becomes gray oxide by losing its oxvgen; 

 we may then tinge the vitrescible matters blue. 



Messrs. Proust and Thalaker found the black oxide at 

 Pavias, in a journey to Valentia. It is also found in cobalt 

 ores, which have been called vltrecus or Hack ores. 



The carbonate and hydrate of cobalt is changed into black 

 oxide, by the contact of the oxy-muriatic acid. 



The nitrous and sulphurous acids dissolve the black oxide, 

 and form with it nitrate and sulphate at the minimum. 



Muriate of Cobalt. — The gray oxide is dissolved with heat 

 in an acid of 15°. The warm or cold solution is of a deep 



Y 3 blue: 



