. 



102 NICCOLITE. 



heated to boiling, in order to expel the excess of the 

 hydrocyanic acid and to convert the cyanide of cobalt 

 and potassium into the cobalticyanide, and is then 

 mixed, whilst still warm, with levigated protoxide of 

 mercury. By this treatment the cyanide of nickel and 

 potassium is decomposed and all the nickel precipi- 

 tated, partly in the form of oxide, partly as cyanide, 

 whilst mercury takes its place. 



The precipitate, when washed and ignited with access 

 of air, leaves pure oxide of nickel behind. 



If the mixture of both oxides, previously to the 

 treatment with hydrocyanic acid and potassa, have 

 been dried and reduced to metal by igniting it in a 

 current of hydrogen (and the metal weighed), the 

 amount of cobalt need not now be determined directly. 



If this be not the case, the solution which still con- 

 tains the cobalt is carefully neutralized with nitric 

 acid, and solution of nitrate of suboxide of mercury, 

 as neutral as possible, added, as long as it produces a 

 white precipitate of cobalticyanide of mercury. After 

 being washed and dried, the precipitate is ignited with 

 access of air, when it is converted into black oxide of 

 cobalt, which, after being weighed, must be reduced 

 by strong ignition in a current of hydrogen, on account 

 of its amount of oxygen varying according to the tem- 

 perature. 



When the nickel-speiss contains lead and sulphur, 

 the same method is used which has been given for the 

 analysis of tetrahedrite, where the compound is decom- 

 posed by heating it in a current of dry chlorine gas. 



Another good method of separation of nickel from 

 cobalt is the following : the solution of both oxides is 

 made as concentrated as possible, and neutralized with 

 potassa, mixed with a concentrated solution of nitrite 

 of potassa, acidified with acetic acid and allowed to 

 stand for twenty-four hours. The yellow precipitate of 

 nitrite of sesquioxide of cobalt and potassa (Co s 3 , 



