OXYGEN. 25 



elaborately executed. Indeed, they have long stood among the classics 

 of physical science, and it is onl}^ recently that they have l)een sup- 

 l^lanted by other measurements. 



For hydrogen three determinations of density gave the following 

 results : 



.06923 



.06932 



.06924 



Mean, .069263, dz .000019 



For ox3''gen four determinations were made, but in tlie first one tlie 

 gas was contaminated by traces of hydrogen, and the value obtained, 

 1.10525, was, therefore, rejected by Regnault as too low. The other three 

 are as follows : 



1.10561 



1. 10564 



1. 10565 



Mean, 1. 105633, ± .000008 



Now, combining the hydrogen and oxygen series, we have the ratio 

 H : : : 1 : 15.9628, ± .0044. According to Le Conte,* Regnault's reduc- 

 tions contain slight numerical errors, which, corrected, give for the density 

 of oxygen, 1.105612, and for hydrogen, .069269. Ratio, 1 : 15.9611. 



A much weightier correction to Regnault's data has already been in- 

 dicated in the discussion of Cooke and Richards' work. He assumed 

 that the globes in which the gases were weighed underwent no changes 

 of volume, but Agamennone,t and after him, but independently, | Lord 

 Ra3deigh showed that an exhausted vessel was perceptibly compressed 

 b}^ atmospheric pressure. Hence its volume when empty was less than 

 its volume when filled with gas. Crafts, having access to Regnault's 

 original apparatus, has determined the magnitude of the correction indi- 

 cated. § Unfortunately, the globe actually used by Regnault had been 

 destroyed, but anotlier globe of the same lot was available. With tliis 

 the amount of shrinkage during exhaustion was measured, and Reg- 

 nault's densities were thereby changed to 1.10562 for oxygen, and 

 ,06949 for hydrogen. Corrected ratio, 1 : 15.9105. Doubtless Dumas 

 and Boussingault's data are subject to a similar correction, and if we 

 assume that it is proportionally the same in amount, the ratio derived 

 from their experiments becomes 1 : 15.9015. 



In the same paper, that which contained the discovery of this correc- 

 tion, Lord Rayleigh gives a short series of measurements of his own. 



* Private communication. See also Phil. Mag. (4), 27, 29, 1S64, and Smithsonian Report, 1S7S, 

 p. 428. 

 t Atti Rendiconti Acad. Lincei, 18S5. 

 X Proc. Roy. Soc, 43, 356. Feb., iSSS. 

 § Compt. Rend., 106, 1662. 



