IS6 Dr Thomson 07i the atomic weight ofNicJcel 



in another 788 parts. Now, when nickel is reduced in this 

 manner it always imbibes a little carbon. It is clear from 

 this that 1000 oxide cannot contain more than 775 parts of 

 metallic nickel. Indeed it is probable that the quantity is not 

 quite so much. Protoxide of nickel, then, according to Ber- 

 thier's experiments, is composed of 



Nickel. Oxygen. 



775 + 225 or 

 3.44 + 1 



So that instead of 5, the atomic weight of nickel, as stated 

 by Lassaigne, the true number is certainly not greater, and 

 probably not so great as 3.44. 



I shall now describe an experiment which I was induced to 

 make on reading the above paragraph in Dr Turnery's book. 

 I need not observe that the most minute attention was paid 

 to the accuracy of the results, and that all the precautions 

 suggested by a great deal of practice in these kinds of investi- 

 gation were employed to guard against mistake. 



When speiss is dissolved in sulphuric acid by means of ni- 

 tric acid and the sulphate of nickel separated by crystalliza- 

 tion, the crystals contain no trace of arsenic acid, or iron, or 

 bismuth, or antimony ; but they are still contaminated with a 

 little sulphate of copper and a little sulphate of cobalt. Five 

 hundred grains of these crystals were dissolved in distilled 

 water, and a current of sulphuretted hydrogen gas was passed 

 through the liquid till the whole copper was precipitated. 

 The sulphuret of copper thus thrown down was digested in 

 aqua regia^ the solution filtered, and a few drops of sulphuric 

 acid added to it. It was then evaporated to dryness, and the 

 sulphate of copper thus obtained being redissolved in water, 

 the black oxide was precipitated by caustic potash, and ig- 

 nited. It weighed 3.33 grains, equivalent to 1 0.4 grains of 

 crystallized sulphate of copper. 



From the sulphate of nickel thus freed from copper, I pre- 

 cipitated the oxide of nickel by means of carbonate of soda. 

 The pale green coloured precipitate was well edulcorated, and 

 being diffused (while still moist) in distilled water, a current 

 of chlorine gas was made to pass through it till every thing 

 soluble was taken up. By this process the oxide of nickel is 



