572 OXIDES OF NICKEL. 



concentrated and set aside to crystallize. The double sulphate 

 of nickel and potash, Ni O, SO 3 + KO, SO 3 + 6HO, forms 

 easily, and may be obtained free from arsenic by a second crys- 

 tallization, (Dr. Thomson.) The perfect separation of small 

 quantities of cobalt and copper, which these crystals may still 

 contain, requires additional processes, for which I must refer to 

 Berzelius, (Traite, I, 486.) With the view of obtaining the 

 metal, the insoluble oxalate of nickel may be precipitated from 

 the preceding salt by oxalate of ammonia, washed, dried, and 

 ignited gently in a covered crucible. The oxalic acid reduces 

 the oxide of nickel, and the metal remains in a spongy state. It 

 is pyrophoric, like manganese and iron prepared in the same 

 manner, if the temperature of reduction has been low. To 

 obtain the metal in a solid mass, it should be fused in a crucible 

 covered with pounded glass. The oxide of nickel is very easily 

 reduced both by carbonic oxide and hydrogen. 



Nickel, when free from cobalt, is silver white, unalterable in 

 air, and highly ductile. Its density, according to Richter, is 

 8.279, and after being forged, 8.666. Nickel is magnetic nearly 

 to the same extent as iron. Magnets composed of this metal 

 lose their polarity at 630 (Faraday.) It is somewhat more 

 fusible than iron. Nickel forms two oxides corresponding with 

 the protoxide and peroxide of iron ; but the double compound 

 of the two oxides of nickel, corresponding with the black oxide 

 of iron, has not been observed. 



Protoxide of nickel, Ni O ; 469.7 or 37.62. May be obtained 

 by the ignition of the carbonate or nitrate of nickel, or by 

 precipitation from its salts by an alkali, as a dark ash- coloured 

 powder, or as a bulky hydrate, of an apple-green colour, 

 NiO, HO. Oxide of nickel is very soluble in acids, but not in 

 potash or soda. Ammonia dissolves it, and forms an azure 

 blue solution, from which oxide of nickel is precipitated by 

 potash, barytes, and strontian, having a considerable tendency 

 to combine with salifiable bases. The solutions of its salts have 

 all a green colour, much more intense than that of the ferrous 

 salts. They are not precipitated by sulphuretted hydrogen 

 when a strong acid is present, but afford a black sulphuret with 

 alkaline sulphurets. The carbonate of nickel is of a pale green 

 colour, and soluble in carbonate of ammonia. 



Peroxide of nickel, Ni 2 O 3 , is obtained as a black powder, 

 by exposing the hydrated protoxide suspended in water to a 



