CHALCOPYRITE. 53 



29. SULPHATE OF COPPER. 



(Blue Vitriol.) 

 CuO,S0 3 



For analysis, the salt is purified by recrystallization. 



To determine the water, a weighed quantity of the 

 dry salt, in the state of fine powder, is heated to about 

 200, until it has become perfectly white, and has 

 ceased to lose weight. 



It is then dissolved in water, and the sulphuric acid 

 precipitated by chloride of barium, as directed in No. 3. 



For the determination of copper, another weighed 

 portion of the salt is dissolved in from 50 to 100 times 

 its weight of water, in a dish or a wide-mouthed flask; 

 the solution is heated until boiling, and the oxide of 

 copper precipitated by caustic potassa, which should 

 not be added in too large excess. The brownish-black 

 precipitate is filtered off, washed with hot water, dried, 

 and weighed. 



To determine the amount of oxygen in the oxide of 

 copper, a freshly-ignited portion is introduced into a 

 weighed bulb-tube, and its weight carefully ascertained ; 

 a stream of dry hydrogen, free from arsenic, is then 

 passed through the tube, the bulb of which is heated 

 to redness with a large flame. When no more aqueous 

 vapor is perceptible, and the oxide is completely re- 

 duced to the metallic state, it is allowed to cool in the 

 stream of gas, and weighed as soon as the hydrogen in 

 the tube has been replaced by atmospheric air. 



30. CHALCOPYRITE. 

 Cu 2 S, Fe 2 S 8 . 



The powdered mineral is introduced into a flask, 

 placed obliquely, and gradually mixed with concen- 



5* 



