Mr. Crum on the Action of Bleaching Powder, frc. 69 



black ; but by triturating upon a piece of glass, it is seen that its real 

 colour is rose. 



Exposed to the action of boiling water, oxygen gas is disengaged 

 from this substance, and brown anhydrous oxide of copper is loft be- 

 hind. Acids dissolvo it, with the liberation of oxygen gas, mixed witli 

 the carbonic acid taken down by tho lime. The solution in nitric 

 acid gives no precipitate with nitrate of silver. Exposed to the air 

 the substance is speedily changed into green carbonate. In attempt- 

 ing to press, and then to dry it in vacuo over sulphuric acid, a largo 

 proportion was changed into tho brown oxide, mixed with carbonate. 

 It can only, therefore, be examined in the moist state, and newly pre- 

 pared. I shall describe tho process by which I have obtained the best 

 results. 



20 grains of black oxide of copper, prepared by calcining the nitrate, 

 are dissolved with the assistance of heat in 70 grains of nitric acid, 

 spec. grav. 1*35. 50 grains of fresh hydrate of lime, sifted through a 

 fine calico, are mixed with 1 lb. solution of bleaching powdor of spec, 

 grav. 1-06, and added to the solution of copper. When the precipitate 

 becomes granular, as already described, it is quickly washed by alter- 

 nate mixing with lime-water, and decanting after subsidence, until the 

 lime-water comes off nearly pure. The precipitate is then put into a 

 wide tube over mercury ; an excess of sulphuric acid is added to it ; 

 and, after pouring out as much as possible of the solution which is 

 thus formed, caustic soda is added to absorb the carbonic acid. In 

 six experiments made in this way, 20 grains oxide of copper produced 

 a compound which yielded of oxygen gas, after the necessary correc- 

 tions — 



1-875 



1-886 



1-748 



1-915 



1-795 



1-747 



Mean 1*828 grains. 



By calculation, 20 grains CuO, changed into Cu 2 3 , ought to yield, 

 by Berzelius' numbers, 1*98 grains of oxygen, or 1*888 by Dr. Thom- 

 son's weights. A nearer approximation than in the foregoing results 

 is scarcely to be expected ; for although there was no perceptible dis- 

 engagement of gas during tho washing of the precipitate in these 

 experiments, it is certain that oxygen always escapes during the 

 time so employed. 



The quantity of lime necessary to the production and stability of 

 this oxide, is not more than one equivalent after saturation of the 

 nitric acid. One atom of lime to three of copper gave only 0*558 

 grains of oxygen gas, instead of the mean quantity of 1*828. Two 



