190 CHROMATE OF LEAD. 



For analysis, it is digested with a mixture of fuming 

 hydrochloric acid and alcohol, when a green solution 

 of sesquichloride of chromium is produced, the lead 

 remaining undissolved as a white chloride. The latter 

 is collected upon a filter, dried at 100, washed with 

 alcohol, and dried at 100. The solution is diluted 

 with water, evaporated to expel the alcohol, and the 

 sesquioxide of chromium precipitated by ammonia; the 

 liquid is heated to ebullition, the precipitate filtered 

 off, ignited and weighed. 



II. For mere qualitative analysis of a specimen of 

 chrome-yellow mixed with the substances mentioned 

 above, it is treated as before, with alcohol and hydro- 

 chloric acid, as little as possible of the latter being 

 employed, in order that the clay may remain un- 

 touched. 



From the solution, the sesquioxide of chromium is 

 precipitated by ammonia ; it always, however, carries 

 down some lime. 



In order to separate them accurately, they must be 

 precipitated together, from the hot solution, by a mix- 

 ture of ammonia and carbonate of ammonia. After 

 drying, the precipitate is fused with three times its 

 weight of a mixture of carbonate and nitrate of potassa, 

 and the fused mass treated with water, which dissolves 

 the chromate of potassa, and leaves the carbonate of 

 lime. 



Or the precipitate, while yet moist, may be digested 

 with hypochlorite of soda, which dissolves the sesqui- 

 oxide of chromium, as chromate of soda, leaving the 

 carbonate of lime undissolved. The solution is then 

 heated to ebullition, in order to decompose any bi- 

 carbonate. 



From the residue, which may consist of the sul- 

 phates of lime, baryta, and lead, the first may be 

 entirely extracted by washing with water, or with a 

 solution of common salt or of sal-ammoniac, in which 



