54 CHALCOPYRITE. 



trated nitric acid in small portions at a time ; the con- 

 tents of the flask are then heated until either the whole 

 is dissolved, or the metals have passed into solution 

 together with a portion of the sulphur, and the un- 

 oxidized sulphur has separated in the form of a yellow 

 powder, or in fused drops of a clear yellow color. 

 The solution is diluted with water, and decanted from 

 any undissolved sulphur, which is well washed, dried 

 in a porcelain crucible, at a gentle heat, and weighed. 

 It is then burnt in order to ascertain whether it contains 

 any metals or quartz, &c. Should the sulphur "be 

 separated in a pulverulent state, it must be collected 

 on a weighed filter, washed, and dried at a very gentle 

 heat. 



From the filtered solution, that portion of the sul- 

 phur which has been converted into sulphuric acid is 

 precipitated by chloride of barium, and the sulphate of 

 baryta treated as in No. 3. Protracted washing with 

 hot water is necessary, since the precipitate has carried 

 down some nitrate of baryta. 



In order to avoid this, the mineral may be dissolved 

 in concentrated hydrochloric acid, with gradual addi- 

 tion of nitric acid, or chlorate of potassa. 



The excess of baryta having been removed from the 

 liquid filtered from the sulphate of baryta by means 

 of sulphuric acid, a slow stream of sulphuretted hydro- 

 gen is passed through the filtrate, until the odor of the 

 gas is distinctly perceptible. The precipitated sulphide 

 of copper is thrown, as rapidly as possible, upon a 

 dried and weighed filter, and well washed with water 

 containing sulphuretted hydrogen. 



It is then dried in the funnel at 200, weighed, a 

 portion of it introduced into a weighed bulb-tube, 

 which is afterwards again weighed, and heated in a 

 stream of hydrogen until it no longer loses any sul- 

 phur. It is thus converted into Cu 2 S, which contains 

 the same amount of copper as the protoxide. The 



