of Colalt and Nickel. 345 



!he state oF arsenlate, by means of potash, which we must 

 add gradually. Ammonia, or a prussiate^ afterwards proven 

 if all the iron has been precipitated. 



Into the filtered solution we make a current of sulphuretted 

 hydrogen to pass j the copper, hismutli, and the whole of 

 the arsenic arc precipitated in the form of sulphurets. 



When the sulphuretted hydrogen occasions no more pre- 

 cipitate, we reduce the liquor in order to crystallize it. The 

 potashed sulphate of nickel, less soluble than the potashed 

 sulphate of cobalt, is the first to crystallize. On repealing 

 the crystallizations, we succeed in separating the two salts; 

 as to the last portions of the salt of nickel, washing them 

 in cold water takes off the sulphate of cobalt they contain. 



All these crystallizations require a bason of fine silver, if 

 we wish to proceed smoothly. 



We ascertain that a salt of nickel is pure, when the preci- 

 pitate dissolved in ammonia abandons this solvent with- 

 out OUT finding any cobalt in it. 



When we jM-ceipitate a sulphate of nickel, we must not 

 be too sparing of the potash : without this precaution we 

 might run the risk of precipitating sulphate with excess of 

 base ; which would alter the purity of the precipitate. 



Carlonale of Nickel. — 100 parts heated in a retort give 

 from 54 to 65 of grccnislr gray oxide at the minimum. 

 When we heat it in contact with the air, the oxide i^ 

 .black. 



The minor oxide becomes carbona^te when exposed to 

 the air. 



Hydrate of Nickel. — All the salts of nickel when thrown 

 into boiling potash are changed into green hydrate ; boiling 

 does not alter the shade of them. Potash neither dissolves 

 the hydrate nor the oxide of nickel. 



The hydrate heated is reduced to gray oxide. 



The oxide is in the state of hydrate in the saline com- 

 binations. The alkalis precipitate it in this state. 



Major Oxide of NickeL — The carbonate and hydrate rise 

 jto the maTi'mum, when we put them in contact with the 

 x)xygenated muriatic acid. Jt is itiore difficuU to oxidize the 

 gray oxide. 



The 



