82 DENSITIES OF OXYGEN AND llVDROfiFV 



19 set down in tlu- t:il>le of results in my [mper. Nor were my measuring tubes too 

 witle for accurate measurement. The fact that my results were consistent shows 

 that the proliable ei-ror of a measui'ement was small, as is computed in the paper. 



At the time when the paper was published it was thought, with what still 

 appeai-.s to be good reason, that the atomic weight of oxygen is veiy nearly 15.88. 

 There was also faii-ly good rea-son for supposing that the ratio of the densities of 

 the two gases was but very little gi'eater than 15.88 ; Lord Ilayleigh had ol)tained 

 the value 15.882, and I had obtained the value, 15.879. My value for the volu- 

 metric ratio therefore seemed consistent with other data, except with what is kn()wii 

 of the divergence of hydrogen and oxygen from Boyle's law. 



But the case is now altered. Scott's excellent work* yields the value at 

 0°, 2.00285. Leduc by two experiments obtains the value, 2.0037. For the i-atio 

 of the densities. Lord Rayleigh's discussion of the published data give the densities 

 of the two gases, at Paris, as 1.42961 gr. and .08991 gr., the ratio of which is 15.900. 

 Fui-thei-, the best I'esult to which I could come from my own experiments, a year 

 ago, is, that the densities at sea level in latitude 45° are 1.4289 gr. and .08987 gr., 

 whose ratio is 15.900. Now if the atomic weight is 15.88 and the ratio of densities 

 is 15.90, the ratio of the volumes is not far from 2.0025. 



It is therefore obvious that whatever physical constant is involved in my 

 former detei-mination, the value obtained in the eudiometer l)y measurement of 

 gases satui-ated with aqueous vapor cannot be applied to pure oxygen and h}iliogen 

 collected in globes whose dimensions are so different from those of the measuring 

 tubes. 



Now, it seems probable that, if sources of constant error can be eliminated, an 

 accurate knowledge of the volumetric ratio, combined w itli the latio <>f the densi- 

 ties, \vould give a value of the atomic ratio which might not be very far behind the 

 methods hitherto employed, either in trustworthiness or even in precision. It was 

 accordingly adjudged worth while to prepai'e apparatus for three new determina- 

 tions by three different processes. The apparatus for two of these new processes 

 has been constructed, and the other could be put togethei- for use in a week. 



In the first proposed method, the volumes of oxygen and hydrogen which are 

 to be condiined, in order to determine the excess of either, were to be measured in 

 the same globes which were used foi- weighing the gases. Two globes were to be 

 filled with hydrogen while they were suii\>unded with ice, and the pressure was to 

 be measured. A globe was to be filled in the same way with oxygen. The three 

 globes were to be of such capacities and the pressures were to be so adjusted, that 

 very nearly thirty litres of hydrogen and fifteen litres of oxygen were to be 

 * Philosophical Tratisactions^ 184, A, 543 (1893) 



