188 CFTROMITE. 



a bright red heat, with an equal weight of nitre and 

 as much carbonate of potassa; from the fused mass, 

 when cool, the chromate of potassa which has been 

 produced is extracted with water. 



The residue, consisting of sesquioxide of iron and 

 variable quantities of alumina and magnesia, is dis- 

 solved in concentrated hydrochloric acid, which gen- 

 erally leaves some undecomposed mineral, and the 

 three oxides are then separated as in No. 81. 



The solution of chromate of potassa usually contains 

 a little alumina, silica and manganic acid, to precipitate 

 which, it is mixed with a little carbonate of ammonia 

 and boiled. 



In order to obtain bichromate of potassa from this 

 solution, it is acidified with nitric acid, concentrated by 

 evaporation, and the salt allowed to crystallize out. 



The chromic acid may be precipitated as chromate 

 of lead, Vy neutralizing the solution with acetic acid 

 and adding acetate of lead. 



To separate the chromium as sesquioxide, the solu- 

 tion, is acidified with sulphuric acid, sulphurous acid 

 added till the solution has an emerald-green color, 

 the sesquioxide of chromium precipitated by ammonia, 

 washed and ignited. 



Or the yellow solution may be exactly neutralized 

 with nitric acid, and the chromic acid precipitated by 

 nitrate of suboxide of mercury. When washed, dried 

 and ignited, the yellowish-red chromate of suboxide of 

 mercury leaves a pure green sesquioxide of chromium. 



II. Chromite may also be quantitatively analyzed 

 by the above process, the fusion being conducted in 

 a platinum crucible, though it will be found that a 

 quantity of ore will be left undecomposed, varying 

 according to the state of division to which it was re- 

 duced. From the solution, after neutralization with 

 nitric acid, the chromic acid is best precipitated by 

 nitrate of suboxide of mercury ; the precipitate is 



