168 METALS AND THEIR COMBINATIONS. 



Cupric sulphate forms large, deep blue crystals, which are 

 easily soluble in water, and have a nauseous, metallic taste. 

 By heating it to about 230 all water of crystallization is ex- 

 pelled, and the anhydrous cupric sulphate formed, which is a nearly 

 white powder. By further heating this is decomposed, sul- 

 phuric and sulphurous oxides are evolved, and cupric oxide is 

 left. 



Cupric carbonate is obtained by the addition of sodium car- 

 bonate to solution of cupric sulphate, when a bluish-green pre- 

 cipitate is formed, which is cupric carbonate with hydrate; by 

 dissolving this in the various acids, the different cupric salts are 

 obtained. 



Ammonio-copper compounds. A number of compounds are 

 known which are either double salts of ammonia and copper, 

 or are derived from ammonium salts and contain copper. Thus, 

 cupric chloride forms with ammonia the compounds : CuCl 2 2NH 3 , 

 CuCl 2 4NH 3 , and CuCl 2 6I^H 3 . Cupric sulphate forms, in like man- 

 ner, cupro-diammonium sulphate, CuSO 4 2KH 3 , or (N 2 H 6 Cu)SO 4 , 

 which is a deep blue compound capable of forming large crystals. 



It is this formation of soluble ammonio-copper compounds 

 which prevents ammonium hydrate from precipitating cupric 

 hydrate from its salts. 



Poisonous properties and antidotes. The use of copper for culi- 

 nary vessels is frequently the cause of poisoning by this metal. 

 A perfectly clean surface of metallic copper is not affected by 

 any of the substances used in the preparation of food, but as the 

 metal is very apt to become covered with a film of oxide when 

 exposed to the air, and as the oxide is easily dissolved by the 

 combined action of water, carbonic or other acids, such as are 

 found in vinegar, the juice of fruits, or rancid fats, the use of 

 copper for culinary vessels is always dangerous. Actual adul- 

 terations of food with compounds of copper have been detected. 



In cases of poisoning by copper the stomach-pump should be 

 used, vomiting induced, and albumen (white of egg) adminis- 

 tered, which forms an insoluble compound with copper. Re- 

 duced iron or a very diluted solution of potassium ferrocyanide, 

 may also be of use as antidotes. 



