ATOMIC WEIGHTS 31 



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

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

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

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



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

 dictated in the discussion of Cooke and Eichards' work. He assumed 

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

 of volume, but Agamennone,^ and after him, but independently,'' Lord 

 Eayleigh showed that an exhausted vessel was perceptibly compressed 

 by atmospheric pressure. Hence its volume when empty was less than 

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

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

 cated." Unfortunately, the globe actually used by Eegnault had been 

 destroyed, but another globe of the same lot was available. With this 

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

 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 Eayleigh gives a short series of measurements of his own. 

 His hydrogen was prepared from zinc and sulphuric acid, and was puri- 

 fied by passage over liquid potash, then through powdered mercuric 

 chloride, and pulverized solid potash successively. It was dried by 

 means of phosphorus pentoxide. His oxygen was derived partly from 

 potassium chlorate, and partly from the mixed chlorates of sodium and 

 potassium. Equal volumes of the two gases weighed as follows : 



H. 0. 



.15811 2.5186, ± .00061 » 



.15807 



.15798 



.15792 



Mean, .15802, ± .000029 



Corrected for shrinkage of the exhausted globe these become- — H, 

 0.15860; 0, 2.5192. Hence the ratio 1 : 15.884, ±.0048. 



^Private communication. See also Phil. Mag. (4), 27, 29, 1864, and Smithsonian Report, 1878, 

 p. 428. 

 ^ Atti Rendiconti Acad. Lincei, 1885. 

 'Proc. Roj'. Soc, 43, 356. Feb., 1888. 

 *Compt. Rend., 106, 1662. 

 ° Arbitrarily assigned the probable error of a single experiment in Rayleigh's paper of 1892. 



