26 



THE ATOMIC WEIGHTS. 



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

 fied by passage over liquid potash, then through powdered mercuric 

 chloride, and then through pulverized solid potash. 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. 



.15811 

 .15807 

 ■15798 

 •15792 



Mean, .15802, 4= 000029. 



O. 

 2.5186, ^ .00061 * 



Corrected for shrinlcage of the exhausted globe these become — H, 

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



In 1892 Rayleigh published a much more elaborate determination of 

 this ratio.f The gases were prepared electrolytically from caustic potasli , 

 and dried by means of solid potash and phosphorus pentoxide. The 

 hydrogen was previously passed over hot copper. The experiments, 

 stated like the previous series, are in five groups ; two for oxygen and 

 three for hydrogen; but for present purposes tlie similar sets may be 

 regarded as equal in weight, and so discussable together. The weights 

 of equal volumes are as follows : 



First set 



H. 



r -15807 

 I .15816 

 J .15S11 



Mean, .15808 I .15S03 

 I .15801 

 ^ .15809 



r .15800 



Second set I ''5820 

 -I .15792 

 I .15788 

 [ -15783 



r -15807 



.I5S0I 



.15817 

 .15790 



.15810 



•1579^ 

 .15802 



I.I5S07 



Mean, .15797 



Third set 

 Mean, .15804 



O. 



2.5182 ] 

 2.5173 I 



2.5172 ! 



2.5'74 I 

 2.5>77 J 



2.5183 1 

 2.5168 j 

 2 5172 \ 

 2.5181 I 

 2.5156 J 



First set. 

 Mean, 2,51785. 



Second set. 

 Mean, 2.5172. 



Mean, 2.5176, ± .00019. 



Mean, .15804, ± .0000 1 9. 



* Arbitrarily assigned the probable error of a single experiment in Rayleigh's paper of 1S92. 

 fProc. Roy. Soc, 50, 448, Feb. 18, 1892. 



