24 THE ATOMIC WEIGHTS. 



Rayleigh 15.89, d= .009 



Noyes 15.S966, it .0017 



Dittmar and Henderson 15.8667, ± .0046 



Leduc 15.881, ±.0132 



Morley 15.8790, dz .00028 



Thomsen, 1895 15-8690, zb .0022 



General mean O ^ 15-8837, rh .00026 



Rejecting Keiser 15.8796, dz .00027 



If we reject all except the determinations of Cooke and Richards, Ray- 

 leigh, Noyes, Dittmar and Henderson, Leduc, Thomsen, and Morley. the 

 general mean of these becomes 15.8794, ± .00027. From this it is evi- 

 dent that Reiser's determinations alone, among the higher values for 0, 

 carry any appreciable weight ; and it also seems clear that the rounded- 

 ofF number, = 15.88, d= .0003, cannot be ver}^ far from the truth ; at 

 least so far as the synthetic evidence goes. 



In discussing the relative densities of oxygen and hydrogen gases we 

 need consider only the more modern determinations, beginning with 

 those of Dumas and Boussingault. As the older work has some his- 

 torical value, I may in passing just cite its results. For the density of 

 hj'drogen we have .0769, Lavoisier; .0693, Thomson ; .092, Cavendish; 

 .0732, Biot and Arago ; .0688, Dulong and Berzelius. For oxygen there 

 are the following determinations: 1.087, Fourcrov, Vauquelin, and Se- 

 guin; 1.103, Kirwan; 1.128, Davy; 1,088, Allen and Pepys ; 1.1036, Biot 

 and Arago; 1.1117, Thomson; 1.1056, De Saussure; 1.1026, Dulong and 

 Berzelius; 1.106, Buff; 1.1052, Wrede.* 



In 1841 Dumas and Boussingault f published their determinations of 

 gaseous densities. For hydrogen they obtained values ranging from .0691 

 to .0695 ; but beyond this mere statement the_v give no details. For 

 oxygen three determinations were made, with the following results : 



I-I055 

 I. 1058 

 I. 1057 



Mean, 1. 10567, zfc .00006 



If we take the two extreme values given above for hydrogen, and re- 

 gard them as the entire series, they give us a mean of .0693, ±: .00013. 

 This mean hydrogen value, combined with the mean for oxj^gen, gives 

 for the latter, wlien H = 1, the density I'atio 15.9538, di .031. 



Regnault's researches, published four years later, ;{: were much more 



* For Wrede's work, see Berzelius' Jahresbericht for 1843. For Dulong and Berzelius, see the 

 paper already cited. All the other determinations are taken from Gmelin's Handbook, Caven- 

 dish edition, v. i, p. 279. 



fCompt. Rend., 12, 1005. Compare also with Dumas, Compt. Rend., 14, 537. 



X Compt. Rend., 20, 975. 



