

244 LORD RAYLEIGH. 



The same is true to the exact value of this atomic weight 

 in reference to that of oxygen ; see True Atomic Weights, 

 pp. 177-183 on the determinations of Dumas, and pp. 

 185-189 on determinations bj Keiser, Morley, Ditmar and 

 Julius Thomsen. 



Lord Rayleigh's Determinations. 



The most important work on hydrogen we have inciden- 

 tally given on page 162, in the density determinations by 

 Lord Rayleigh, namely, H = 1.0028 for O = 16 exactly. 



An earlier determination by the same authority is 1.0062; 

 see p. 161. This was in 1893, before the discovery of argon. 

 The above, much smaller value was obtained after this dis- 

 covery, which incidentally increased the experience in this 

 work very greatly. 



We, therefore, may conclude H = 1.0028 to represent an 

 upper limit for hydrogen. 



This, the most difficultly purified, most difficultly 

 retained pure gas, shows, in the hand of this master, a 

 density-atomic weight of 1.006 in 1893, and only 1.003 in 

 1897. 



We conclude that the true atomic weight of absolutely 

 pure hydrogen is i.ooo, to which Lord Rayleigh approached 

 within 0.006 in 1893, and to within half that limit (0.003) * n 

 1897. 



Every impurity necessarily raises the density of this, the 

 lightest of all gases. 



Morley's Determinations. 



The most pretentious work of Morley on hydrogen, has 

 appeared since the publication of our work of 1894. It was 

 (C recommended for publication by F. W. Clarke," and pub- 

 lished in grand style by the Smithsonian Institution as No. 

 980 of its <{ Contributions to Knowledge," in 1895. 



I do not deem it necessary to enter upon the " complete 

 syntheses" of water by Morley; for this element, it is pre- 

 ferable to use density determinations, as for nitrogen. We 



