NICCOLITE. 99 



II. Or the powdered ore is mixed with 2 parts of 

 dry soda, and 2 of saltpetre, in a clay crucible, and 

 ignited for a considerable time. After the mass has 

 cooled, all the arsenate of potassa is extracted by hot 

 water, and the remaining oxide washed. 



III. Or the ore is mixed with 2 parts of dry soda 

 and If parts of sulphur, in a clay crucible, and gradu- 

 ally heated to redness. It is kept at a low red heat for 

 some time, being well covered. The sulph-arsenate 

 and sulphide of sodium are extracted by water, after 

 the mass has cooled, and the crystalline sulphide of 

 nickel washed by decantation. 



The mixture of oxides remaining behind in the 

 first and second cases is dissolved in hot concentrated 

 hydrochloric acid, that of the sulphides, in the third 

 case, in hydrochloric acid with gradual addition of 

 nitric acid and with application of heat. 



The solution is heated to about 70, and during that 

 time, and until it has cooled, saturated with sulphuret- 

 ted hydrogen; it is then allowed to stand in a closed 

 vessel for twenty-four hours, when copper, bismuth, 

 and a residue of arsenic are precipitated. 



The arsenic is more easily precipitated if first con- 

 verted into arsenious acid by heating with sulphurous 

 acid. The solution must be freed from an excess of 

 sulphurous acid by boiling, before the sulphuretted 

 hydrogen is passed into it. 



The sulphuretted hydrogen having been expelled 

 by heat, the solution is filtered, heated to boiling, and 

 precipitated by carbonate of soda; the precipitate, 

 containing all the nickel, cobalt, and iron, is thoroughly 

 washed. 



It is then, whilst still moist, treated and digested 

 with an excess of a hot saturated solution of oxalio 

 acid, when all the iron is dissolved, and the nickel and 

 cobalt are left in the form of oxalates. They are 



