Bleaching Powder on the Salis of Copper and Lead. 295 



the precipitate, changes colour, and both at last become an 

 insoluble purplish black powder. Oxygen gas is disengaged 

 during the latter part of this process, and continues for some 

 time to prevent the precipitate from subsiding; but after 

 twenty or twenty-four hours the evolution of gas nearly 

 ceases, the particles having united into larger grains sink 

 to the bottom of the vessel into moderate bulk, and may then 

 readily be separated from the soluble matters, by repeated 

 mixing with cold lime-water and drawing off the clear liquid 

 with a syphon. The precipitate thus obtained is, as I have 

 said, nearly black ; but by triturating upon a piece of glass 

 it is seen that its real colour is rose-red. 



Exposed to the action of boiling water oxygen gas is dis- 

 engaged from this substance, and brown anhydrous oxide of 

 copper is left behind. Acids dissolve it, witn the liberation 

 of oxygen gas, mixed with the carbonic acid taken down by 

 the lime. The solution in nitric acid gives no precipitate 

 with nitrate of silver. Exposed to the air the substance is 

 speedily changed into the green carbonate. In attempting to 

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

 proportion was changed into the brown oxide mixed with car- 

 bonate. It can only therefore be examined in the moist state 

 and newly prepared. I shall describe the process by which 

 I have obtained the best results. 



Twenty grains of black oxide of copper, prepared by cal- 

 cining the nitrate, are dissolved with the assistance of heat in 

 70 grs. of nitric acid, specific gravity r35. Fifty grains of 

 fresh hydrate of lime, sifted through fine calico, are mixed 

 with 1 lb. solution of bleaching powder of specific gravity 1'06, 

 and added to the solution of copper. When the precipitate 

 becomes granular, as already described, it is quickly washed, 

 and decanted until the lime water comes off nearly pure. The 

 precipitate is then put into a wide tube over mercury, an ex- 

 cess of sulphuric acid 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 experi- 

 ments made in this way, 20 grs. of oxide of copper produced 

 a compound which yielded of oxygen gas, after the necessary 

 corrections, — 



1-875 

 1-886 



Mean 



