ATOMIC WEIGHTS 33 



Combining this with Eegnault's density for oxygen, as corrected by 

 Crafts, 1.10562, ± .000008, we get the ratio H : : : 1 : 15.890, ± .0067. 



Leduc, working by Eegnault's method, somewhat modified, and cor- 

 recting for shrinkage of exhausted globes, gives the following densities ' : 



H. 0. 



.06947 1.10501 



.06949 1.10516 

 .06947 



Mean, .06948, ± .00006745 



The two oxygen measurements are the extremes of three, the mean 

 being 1.10506, ± .0000337. Hence the ratio 1 : 15.905, ± .0154. 



In a later memoir Leduc" gives two more measurements of the density 

 of oxygen. They are 1.10527 and 1.10521. If we include these in series 

 with the other values the mean becomes 1.10514, ±.0000321. The use 

 of this figure in subsequent combinations of data has an insignificant 

 effect upon the computations. It raises from 15.905 to 15.906. 



The first two hydrogen determinations were made with gas produced 

 by the electrolysis of caustic potash, while the third sample was derived 

 from zinc and sulphuric acid. The oxygen was electrolytic. Both gases 

 were passed over red-hot platinum sponge, and dried by phosphorus 

 pentoxide. 



Much more elaborate determinations of the two gaseous densities are 

 those made by Morley.^ For oxygen he gives three series of data; two 

 with oxygen from potassium chlorate, and one with gas partly from the 

 same source and partly electrolytic. In the first series, temperature and 

 pressure were measured with a mercurial thermometer and a mano- 

 barometer. In the second series they were not determined for each 

 experiment, but were fixed by comparison with a standard volume of 

 hydrogen by means of a differential manometer. In the third series the 

 gas was kept at the temperature of melting ice, and the mano-barometer 

 alone was read. The results for the weight in grammes, at latitude 45°, 

 of one litre of oxygen are as follows : 



First Series. Second Series. Third Series. 



1.42864 . 1.42952 1.42920 



1.42849 1.42900 1.42860 



1.42838 1.42863 1.42906 



1.42900 1.42853 1.42957 



1.42907 1.42858 1.42910 



'Cumpt. Rend., 113, 186. 1891. 



- Ann. Chim. Phys. (7), 15, 29. 1898. In C. R., 148, 42, Leduc claims that the probable error 

 of his H is only + .00001. 

 ■* Paper already cited, in the gravimetric portion of this chapter. 



