PROTOXIDE OF COPPER. 581 



obtained on mixing a solution of 1 part of sulphate of copper 

 and 2i parts of protosulphate of iron, with a solution of iodide 

 of potassium. 



Protoxide of copper, Black oxide of copper, CuO; 495.7 or 

 39.J1. The base of the ordinary salts of copper. It is formed 

 by the oxidation of copper at a red heat, but is generally 

 prepared by igniting the nitrate of copper. It is black like 

 charcoal, and fuses at a high temperature. This oxide is re- 

 markable for the facility with which it is reduced, at a low red 

 heat, by hydrogen and carbon, which it converts into water and 

 carbonic acid. It is that property which recommends oxide of 

 copper for the combustion of organic substances, in close vessels, 

 by which their ultimate analysis is effected. The protoxide of 

 copper precipitates as a blue hydrate, when a solution of sul- 

 phate of copper is allowed to fall, drop by drop, into solution of 

 potash. This hydrate is decomposed in boiling water, and 

 becomes brown, but is apt to carry down a little of its precipi- 

 tating alkali, of which it is difficult to deprive the brown oxide 

 altogether by washing. 



The oxide of copper dissolves readily in ammonia, affording a 

 deep azure blue solution. But for this experiment a small 

 quantity of acid, or of a salt of ammonia, must be present, the 

 solution appearing to be truly that of a subsalt of copper in 

 ammonia, and pure ammonia not dissolving equally pure oxide 

 of copper. Dr. Kane obtained, on one occasion, an insoluble 

 ammoniacal oxide of copper, by precipitating chloride of copper 

 by ammonia, of which the composition was 3 CuO + 2NH 3 + 6 HO. 



Oxide of copper is a powerful base. Its salts are generally 

 blue or green, when hydrated, but white when anhydrous. 

 Although neutral in composition, they have a strong acid reac- 

 tion. They are poisonous; but their effect upon the animal 

 system is counteracted in some degree by sugar. Liquid albu- 

 men forms insoluble compounds with these salts, and is an 

 antidote to their poisonous action. Copper is separated in the 

 metallic state from its salts by zinc, iron, lead, and the more 

 oxidable metals, which are dissolved and take the place of the 

 former metal. Copper is completely precipitated by sulphuretted 

 hydrogen, as a dark brown or black sulphuret, even from acid 

 solutions. The ferrocyanide of potassium gives a characteristic 

 brown precipitate with the salts of copper. Its salts also im- 

 part a green colour to flame. The black 'oxide of copper 



