ATOMIC WEIGHTS 39 



In 1891 an elaborate paper b}^ Morley^ appeared, in which twenty 

 concordant determinations of the volumetric ratio gave a mean value of 

 2. 00023, ±.000015. These measurements were made in eudiometer tubes, 

 and were afterwards practically discarded by the author. In his later 

 and larger paper,'' however, he redetermined the ratio from the density 

 of the mixed electrolytic gases, and found it to be, after applying all 

 corrections, 2.00274. The probable error, roughly estimated, is .00005. 

 Morley also reduces Scott's determinations, which were made at the tem- 

 perature of the laboratory, to 0°, when the value becomes 2.00285. The 

 mean value of both series may therefore be put at 2.0028, ± .00004, with 

 sufficient accuracy for present purposes. Leduc's' single determination, 

 based upon the density of the mixed gases obtained by the electrolysis 

 of water, gave 2.0037; but Morley shows that some corrections were 

 neglected. This determination, therefore, may be left out of account. 



There is also a corroborati^'e measurement by Eayleigh,* who assigns 

 to the ratio the value 2.0026. This agrees well with the figures given by 

 Scott and Morley. Eayleigh also gives measurements of gaseous den- 

 sities at very low pressures, and obtains molecular ratios differing con- 

 siderably from those ordinarily found. At atmospheric pressure, for 

 example, H=: 1.0075; and at very low pressures its atomic weight becomes 

 1.0088. 



ISTow, including all available data, we have as a mean value for the 

 density ratio: 

 (A.) H:0::l:15.8948, ±.00048 



or, omittting Morley's rejected series, 



(B.) H:0::l:15.8991, ±.00048 



Correcting these by the volume ratio, 2. 0028, ±.00004, the final result 

 for the atomic weight of oxygen, in terms of the hydrogen unit, and as 

 computed from the gaseous densities becomes — 



From A = 15.8726, ± .00058 



From B = 15.8769, ± .00058 



Combining these figures with the values deduced from the syntheses 

 of water, rejecting nothing, we have — 



By syntheses of water O = 15.8779, ± .00016 



By gaseous densities O = 15.8726, ± .00058 



General mean = 15.8775, ± .00015 



1 Amer. Journ. Sci. (3), 46, 220 and 276. 

 * Already cited with reference to syntheses of water. 



'Compt. Rend., 175, 311. 1892. In a later, more complete memoir, Ann. Chim. Phys. (7), 

 15, 49, Leduc gives the figure 2.0034. He also criticizes Morley's deductions. 

 *Proc. Roy. Soc, 73, 153. 1904. 



