RICHARDS AND CUSHMAN, — ATOMIC WEIGHT OF NICKEL. 333 



found after half an hour, and then at the end of many hours. Since the 

 boat was cool before having been introduced into the bottle, two suc- 

 cessive weighings thus made never differed from one another by amounts 

 beyond the limit of error of weighing. Spongy nickel evidently does 

 not oxidize in dry air. 



It is obviously a matter of great importance to discover whether or not 

 the material prepared in this way contains weighable amounts of occluded 

 hydrogen. According to the experiments of Neumann and Streintz* 

 who worked with reduced metals, two cubic centimeters of the gas were 

 occluded by each gram of spongy nickel. This amount would alter the 

 observed atomic weight by only about the fortieth of one per cent ; but 

 since we are aiming at even greater accuracy, the matter should evidently 

 be probed to the bottom. 



In the first place, carefully weighed nickel remaining from one of the 

 analyses recorded below was ignited in a Sprengel vacuum at perhaps 

 550°, For fear of losing some sodic bromide a higher temperature 

 could not be employed. No appreciable loss of weight occurred and no 

 gas was evolved during this process, which was repeated with several 

 specimens ; hence there seemed to be good reason to believe that no 

 hydrogen was occluded by the metal in our experiments. In order to 

 prove the matter, one and a half grams of spongy nickel reduced from 

 the bromide and allowed to cool in hydrogen was oxidized by heating in 

 a current of dry air, which was subsequently passed over red hot cupric 

 oxide, and through a carefully weighed tube containing phosphoric oxide. 

 Since the absorption tube did not gain in weight, no water could have 

 been formed during the combustion, and hence no hydrogen could have 

 been occluded. 



Treated in exactly the same way, four grams of nickel prepared by 

 the reduction of the oxide yielded about three milligrams of water, or 

 about half the amount found by Neumann and Streintz. This agreement 

 is sufficient to show that these investigators were not mistaken in their 

 conclusions, and that the permeability of nickel is enormously modified 

 by minor circumstances. 



Is the presence of the sodic bromide, otherwise so objectionable, the 

 agency which prevents the occlusion in our case, or does the volatility of 

 nickelous bromide allow its metal to be deposited in a form more cohe- 

 rent than that remaining from the oxide ? The attempt to answer these 



* Monatshefte fur Chemie, XII. 6i0 (1891). Berichte der d. ch. Gesell., XXV., 



1872. 



