1907.] 



on High Vacua and Heliuni. 



751 



in 19 minutes. The annexed table gives the observations. The law- 

 connecting pressure and time in this particular apparatus seems to be 

 given by a formula of the type 



log(f)log(*) = . 



where t and 7; are time and pressure, and ale are constants. 



Chaecoal Occlusiox Pressures of Hydrogen axd Xitrogex. 



The apparatus sketched in Plate IL, illustrates how the gas concen- 

 tration, pressure and temperature are measured. The mass of char- 

 coal E, immersed in liquid air, is used for the preliminary exhaustion 

 of the McLeod gau^e G, and the charcoal in C to be used in the 

 experiments, and is then sealed off at S. Afterwards the bulb C is 

 placed in a large spherical vacuum flask containing liquid oxygen 

 which can be made to boil at any definite temperature under diminished 

 pressure measured on the manometer Pt. The volume of gas 

 admitted into the charcoal is measured by the burette D and pipette 

 P and the corresponding occlusion pressure at any concentration and 

 temperature below that of 90' abs., by the gauge G. 



For small concentrations the relation between the pressure and 

 the concentration of different gases in presence of charcoal, shows 

 very great variation, all being at the same temperature. The follow- 

 ing table gives the comparison between hydrogen and nitrogen at the 

 temperature of liquid air, 25 grammes of charcoal being used. 



Hence we see that 15 c.c. of hydrogen produced nearly the same 

 pressure (0'0645 mm.) as 2500 c.c. of nitrogen (its pressure being 



