Intelligence and Miscellaneous Articles. 231 



when arsenite of potash or soda is mixed with a solution of any salt 

 of copper, and a caustic alkali is added to it. It also takes place 

 on mixing arsenite of potash or soda with hydrated oxide of copper, 

 and then adding a caustic alkali ; the change is very slow with heated 

 oxide of copper. Upon examination of the precipitate after washing 

 the following action takes place. 



Diluted sulphuric acid is coloured blue, and metallic copper is 

 left ; muriatic acid added in a small quantity changes the preci- 

 pitate into a white powder, a larger quantity gives a brown solution ; 

 from which it follows that the precipitate is a suboxide of copper; 

 this is confirmed by the experiments which follow. The reduction 

 of the oxide of copper can only be attributed to the effect of the 

 arsenious acid, which it is to be observed is converted into arsenic 

 acid. 100 parts of arsenious acid, taking 161 parts of oxygen for 

 its conversion into arsenic acid will therefore convert 159"6 of oxide 

 copper into suboxide. In order to ascertain whether the reduction 

 of the oxide of copper by the addition of the ingredients in this 

 proportion would also result, as well as by the employment of arse- 

 nite of copper in which a larger quantity of arsenious acid was pre- 

 sent, the following experiments were made : 



1*6 gramme oxide of copper were dissolved in very dilute sul- 

 phuric, and 1 grm. of arsenious acid was dissolved in a solution of 

 10 grms. of caustic soda of specific gravity 1 -20 ; the solutions were 

 mixed together cold, and 20 grms. caustic alkali were added ; the 

 mixture was placed in a warm situation and often stirred j the co- 

 lour soon changed and the precipitate completely formed. The so- 

 lution was poured off, and the suboxide copper was washed with 

 warm water and separated. 



The solution was neutralized by nitric acid ; sulphate of copper 

 gave a blue precipitate, and nitrate of silver a reddish brown pre- 

 cipitate, indicating the presence of arsenic acid. 



The washed precipitate mixed with boiled water acidulated by 

 sulphuric acid changed immediately to brown flakes of metallic 

 copper ; the supernatant liquid was poured off, and the copper 

 well washed with boiling water, collected and weighed; it weighed 

 0-62 gram. 



One half of 16 gramme of oxide of copper will give 0*638 me- 

 tallic copper. The result of the foregoing experiment agrees nearly 

 with this; it may be considered therefore that all the oxide of cop- 

 per is reduced by arsenious acid to the state of suboxide. If this 

 experiment were repeated by taking double the quantity of arsenious 

 acid the same result would take place, and the oxide of copper 

 would be only reduced to the state of suboxide. 



When caustic ammonia is used, the oxide of copper is only par- 

 tially converted into suboxide. The solution remains perceptibly 

 blue, and only becomes colourless upon the addition of a caustic 

 alkali. If the blue ammoniacal solution is supersaturated by sul- 

 phuric acid, metallic copper is precipitated. 



The carbonated alkalies occasion no perceptible reduction of 

 oxide of copper, which is also the case with caustic lime. 



Upon considering the reducing power of arsenious acid on oxide 



