328 Dr. Thomas Thomson on the Atomic Weight 



some change in the oxide of nickel. For there can 

 be no mistake either respecting the sulphuric acid or 

 water. 



This circumstance induced me to turn my attention to 

 the oxide of nickel, which was obtained by mixing sulphate 

 of nickel with caustic spda, edulcorating the precipitate, 

 and exposing it to a red heat. The oxide of nickel obtained 

 in this way is a beautiful black matter concreted into small 

 lumps, having considerable lustre, and easily reduced to 

 powder. It is tasteless and insoluble in water. But it 

 dissolves slowly in sulphuric and nitric acids. During the 

 solution an effervescence takes place, and oxygen gas is 

 given out in abundance. This remarkable evolution of 

 gas, which uniformly took place, led to the conclusion, 

 that the oxide was not the protoxide, but the peroxide of 

 nickel ; and that it had been peroxidized during the pro- 

 cess of ignition. 



To determine this point, I put 10 grains of it into a small 

 ball blown in a green glass tube. This tube was attached 

 to another, containing fragments of fused chloride of 

 calcium, connected with a small Woulfe's bottle, in which 

 hydrogen gas was evolved by the solution of zinc in dilute 

 sulphuric acid. After all the common air had been expelled, 

 and the tubes filled with hydrogen gas, a spirit lamp was 

 placed under the oxide of nickel, and kept under it till it 

 was gradually raised to a red heat. During the whole pro- 

 cess a current of hydrogen gas was passing through the 

 tube, and it continued to pass till the experiment was finished 

 and the apparatus cold. It is well known, that under these 

 circumstances, the oxide of nickel is rapidly reduced to the 

 metallic state. The object of the experiment was to deter- 

 mine the loss of weight which the oxide of nickel would 

 sustain when reduced to the metallic state. The experiment 

 was made thrice successively. The following table shows 

 the results : 



Oxygen. 



1. 10 grains oxide when reduced, lost 3*33 grains. 



2. 10 2-95 



3. 10 • . . 3-57 



Mean 328 



