ATOMIC WEIGHTS. 535 



hold any fair quantity of hydrogen, and the difficulty of 

 weighing it accurately. This was done, however, after the 

 manner of Regnault, by having a counterpoise of the same 

 external volume, and the weighings obtained seemed to be 

 satisfactory in the highest degree even under great varia- 

 tions in the atmospheric conditions. Perhaps the most pro- 

 bable source of error is in the assumption that the increase 

 in weight of the globe is due to absolutely pure hydrogen. 

 •. Jxygen may be completely removed from hydrogen con- 

 taminated with it, but this is not so with nitrogen. A trace 

 of nitrogen therefore in the hydrogen would escape detec- 

 tion and defy removal and so cause serious error. An 

 error in Regnault's method of weighing gases was pointed 

 out by Lord Rayleigh after Cooke and Richards' paper 

 was published ; this was the correction for the difference in 

 buoyancy of the globe, caused by differences in the ex- 

 ternal and internal pressures, the globe being naturally 

 smaller when exhausted than when filled with gas at about 

 the atmospheric pressure. Their corrected results give 

 H = 1 '00825. 



Keiser weighed his hydrogen in the form of palladium 

 hydride, expelling the hydrogen by heat and passing it, 

 mixed with nitrogen, over red hot copper oxide, the water 

 formed being collected and weighed in much the usual way. 

 His results are much higher than those of most of the recent 

 workers in this field, as they point to 15*9492 as the atomic 

 weight of oxygen, if O = 16, H = 1*003 18. His paper is 

 too vague in many points for criticism ; we are told that 

 "chemically pure Zinc, free from arsenic " was used for 

 making the hydrogen, that pure nitrogen was used, but no 

 description of how this was- obtained is given, his weights 

 were corrected by the "well-known method of adjustment," 

 and such like statements abound throughout the paper. 

 Keiser seems to have unbounded confidence in the drying 

 power of one phosphoric anhydride tube even when passing 

 large quantities of inert gas saturated with aqueous vapour 

 through it at a considerable rate, for we are told that ''a 

 combustion including the weighings could be made in four 

 hours," also that the various pieces of the apparatus after 



