1820.] Physical Science during the Year 1819. 45 



According to M. Longchamp sulphate of magnesia cannot be 

 deprived of its water unless it be exposed to a white heat. 

 Hydrate of magnesia he finds composed of 



Magnesia 52-997 



Water 47-003 



100-000 



After being exposed to a red heat, this hydrate still continues 

 composed of 



Magnesia 79-218 



Water 20-782 



100-000 



According to M. Longchamp the best way.. of separating lime 

 from magnesia is to precipitate by carbonate of ammonia, which 

 throws down the lime in the state of a carbonate without throw- 

 ing down any magnesia. The magnesian solution is then to be 

 evaporated to dryness, and calcined to drive off the ammonia. 

 The magnesian salt is now to be dissolved in water, and the 

 magnesia precipitated by caustic potash. 



He finds that the carbonate of magnesia is soluble in sulphate, 

 nitrate, and muriate of potash and soda. (Ann. de Chim. et de 

 Phys. xii. 255.) 



17. Salts of Nickel. — M. Berthier has pubhshed some recent 

 analyses of different salts of nickel which it may be worth while 

 to state here. 



(1.) Arseniate of Nickel. — This salt was obtained by mixing 

 arsenic acid with muriate of nickel, and precipitating by an 

 excess of an alkaline carbonate. This arseniate he found com- 

 posed of very nearly equal parts of acid and base. This would 

 be nearly a compound of one atom arsenic acid and three atoms 

 protoxide of nickel. 



(2.) Sulphate of Nickel. — This salt, according to the analysis 

 of Berthier, is composed of 



Sulphuric acid 52-2 5-000 



Protoxide of nickel 47-8 ...... 4-578 



100-0 



(3.) Carbonate of Nickel. — This salt is composed of 



Carbonic acid 14*0 



Protoxide of nickel 47*5 



Water 38-6 



100-0 

 This carbonate is of a fine apple-green colour. It is obtained 



