232 Mr GRAHAM on the Law of 



This receiver was also nearly filled at the commencement of the 

 experiment with hydrogen gas, and the quantity of gas not- 

 ed, the tube being graduated. The hydrogen in this standard 

 receiver contracted -^A part during the experiment. We have 

 therefore to increase the quantity of air found ultimately in the 

 diffusion-receiver by T \d part. In this way the residuary air is 

 increased to 229.8 measures, 12 of which, or, more correctly, 

 11.85 ( 12 V(12)), were present from the beginning. The 

 temperature was also 68 at the end of the experiment, the same 

 as at the beginning. The ultimate contents of the diffusion- 

 instrument may be stated with sufficient accuracy as follows : 



Air and vapour originally present, . 11.85 

 Dry air which has entered, . . . 212.84 

 Vapour in do. . . . . . 5.11 



229.80 



The conclusion is, that 823.83 measures dry hydrogen have 

 been replaced by 212.84 dry air. Now, 



* = 3.87 = diffusion-volume of hydrogen. 



The diffusion-volume of hydrogen comes out above the theoreti- 

 cal number in this experiment, but an addition of not more than 

 2 per cent, to the quantity of return-air, would reduce it below 

 the theoretical number. The quantity of vapour which was 

 supported by the hydrogen at the commencement of the experi- 

 ment was 19-17 measures, but at the end of the experiment we 

 find only 5.11 measures vapour; the difference has condensed, 

 from the loss of a permanently elastic fluid necessary to support 

 it. 



As the quantity of hydrogen and of return-air is amplified 

 in the same proportion by vapour, provided the temperature be 

 the same at the beginning and end of the experiment, it is unne- 



