RICHARDS AND BAXTER. — ATOMIC WEIGHT OF COBALT. 355 



being heated to constant weight in the usual way. Upon correcting the 

 weight of the bottle for the difference in weight of nitrogen and air, the 

 weights obtained by both methods agreed perfectly. 



The resulting cobalt was in the form of a gray metallic sponge, which 

 showed no traces of oxidation upon standing in air. Since previous 

 work by other experimenters * is not unanimous as to the occlusion of 

 hydrogen by cobalt under these circumstances, it seemed desirable to us 

 to obtain more evidence on this point. Accordingly, in several analyses 

 the boat containing the cobalt was placed in a hard glass tube sealed at 

 one end. After the air had been exhausted by means of a Sprengel 

 pump, the tube was heated to about 500°, the highest temperature used 

 in the reduction. In no case was a measurable quantity of gas evolved, 

 and the cobalt did not lose in weight ; hence it would appear that cobalt 

 prepared from the bromide does not possess the property of occluding 

 important amounts of hydrogen when heated in the gas. 



To avoid any possibility of error, two and a half grams of cobalt, 

 freshly reduced from the bromide aud allowed to cool in hydrogen, were 

 subjected to quantitative combustion in the manner already described in 

 the paper upon nickel. Only five tenths of a milligram of water were 

 formed ; and even the repeated reduction and combustion of the residual 

 oxide yielded only a milligram. Evidently the amount of hydrogen 

 occluded was very small. On the other hand, cobalt reduced originally 

 from the oxide, when treated in the same way, was found to contain 

 about fifteen times its volume of hydrogen and when allowed to remain 

 in hydrogen several hours, it was found to have absorbed amounts com- 

 parable to those found by Neumann and Streintz.f A fuller statement 

 of the experiments will be reserved for a future paper upon the nature 

 and causes of these singular irregularities ; for the present, it is sufficient 

 to have shown that cobalt, like nickel, reduced from the bromide, does 

 not retain enough hydrogen to vitiate the results recorded below. 



It is perhaps worth while to state also that the empty platinum boat 

 was tested as to its power of absorbing weighable amounts of hydrogen. 

 After ignition and cooling in the gas, and bottling in dry air as usual, it 

 was found to have gained 0.02 milligram when compared with its weight 

 after ignition in air. Evidently the occlusion of hydrogen, if measurable 

 at all, is balanced by adsorption of air ; hence for our purpose it may be 

 neglected. 



* Neumann and Streintz, Monatshefte fiir Chem., XIT. 642; Berichte d. d. ch. 

 Gesell., XXV., 187R ; Henipel and Thiele, Zeitschr. Anorg. Chem., XI. 93. 

 t Loc. cit. 



