1892.] Relative Densities of Hydrogen and Oxygen. 



Oxygen. 



459 



The means here exhibited give the.weights of the two gases as they 

 would be found with the globe at 12 C., and the barometers at 60 F. 

 and at 30 inches. The close agreement of the mean temperatures for 

 the two gases shows how little room there is for systematic error de- 

 pendent upon imperfections in the barometers and thermometers. But 

 the results still require modification before they can be compared with 

 the view of deducing the relative densities of the gases. 



In the first place, there is a systematic, though minute, difference in 

 the pressures hitherto considered as corresponding. The terminal of 

 the blow-off tube is 33 inches below the centre of the globe at the time 

 of filling. In the one case this is occupied by hydrogen, and in the 

 other by oxygen. If we treat the latter as the standard, we must 

 regard the hydrogen fillings as taking place under an excess of pres- 

 sure equal to y-f of the weight of a column of oxygen 33 inches high ; 

 and this must be compared with 30 inches of mercury. Hence, if we 

 take the sp. gr. of oxygen under atmospheric conditions at O'OO] 4, 

 and that of mercury at 13'6, the excess of pressure under which the 

 hydrogen was collected is as a fraction of the whole pressure 



and 0-000106x0-158 = 0'000017. This, then, is what we must sub- 

 tract from the weight of the hydrog i on account of the difference of 

 pressures due to the gas in the blow-off tube. Thus 



H = 0-157998, = 2-51724. 



[These numbers are not quite comparable with those given in the 

 former communication, inasmuch as the standard temperature then 

 used for the barometers was 55 F. Reduced so as to correspond to 

 60, the former numbers become 



H = 0-15797, 



= 25174. 



