68 Mr. Crum on the Action of Bleaching Powder, Sfc, 



Idth March, 1845. Tlie President in the Chair. 



A report from the committee appointed to arrange the Conversa- 

 tional Meeting was road and approved of. The following paper was 

 read : — 



X. — On the Action of Bleaching Powder on the Salts of Copper and 

 Lead. By Walter Crum, F.R.S., Vice-President of the Society. 



In February, 1843, I read to the Philosophical Society of Glasgow 

 an account of a rose-coloured oxide of copper which I had obtained 

 by the action of bleaching powder and lime upon nitrate of copper. 

 Although I had then made numerous analyses of this substance, pre- 

 pared under a variety of circumstances, I had been unable to obtain 

 from it the full amount of oxygen which a definite compound must 

 contain, and delayed therefore to make it farther known until I should 

 have the opportunity of producing it in a purer form. In the mean- 

 time the rose-coloured substance has been noticed, and correctly de- 

 scribed by Kriiger of Berlin, as a combination of the oxide, or, as he 

 calls it, of cupric acid, with lime. Having completed my experiments 

 on this subject, as far as my leisure will permit, I shall now state the 

 results I have obtained. 



When the hydrated oxide of copper is added to a solution of bleach- 

 ing powder it soon changes colour, particularly when assisted by heat, 

 and becomes brown. Oxygen gas is then plentifully disengaged, and 

 the effervescence continues till the whole of the hypochlorite of lime 

 is decomposed. The brown precipitate suffers no change during this 

 decomposition ; when separated from the soluble matters, it is found 

 to contain no chlorine, and no excess of oxygen ; it is anhydrous oxide 

 of copper. Hypochlorite of soda produces the same effects. 



If we add nitrate of copper to a solution of bleaching powder in 

 which is mixed a considerable quantity of lime, and previously cooled 

 to the freezing point of water, a bluish green precipitate is formed. 

 When the precipitate subsides, we find the solution of a fine blue colour, 

 and containing copper ; but in what state I have not examined. As the 

 heat advances to the ordinary temperature, the copper in solution, as 

 well as 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 



