r arious Gases by the a Particles of Radium. 



541 



For I have not been able to prevent the leakage of air 

 into the apparatus when raised above ordinary temperatures, 

 and it is necessary to measure and allow for the air present 

 in each experiment. The apparatus holds very well when 

 not heated : but it is sometimes necessary to raise the tem- 

 perature to 60° or 70° C. in order to obtain a sufficient 

 density of the vapour under treatment. Fortunately, however, 

 the air present may be a considerable fraction of the gas 

 when measured by pressure, and yet be of little importance 

 when measured in terms of the energy spent in it. Thus the 

 correction for air present is usually quite small, as will be seen 

 from a consideration of the numerical results in § 2. 



The assumption is by no means an obvious one. If any 

 part of the ionization in a gas is secondary, and is due to 

 radiation originating in one molecule and acting on a neigh- 

 bouring molecule, it might well be that complications would 

 arise in a mixture of gases. I have made several direct attempts 

 to find whether any such effects existed : the results of some 

 of them are shown in the following tables. Each table refers 

 to a set of experiments carried out. consecutively. The 

 percentage of gas in each mixture is determined from the 

 stopping power, and the percentage of energy spent in the gas 

 is then calculated. The value of III for the gas i* calculated 

 by multiplying the observed value for air by the specific 

 ionization of the gas, as taken from the final tables given 

 at the end of the paper. For example, in the first set 

 M for air is 198"5, and EI for ethyl chloride is taken to be 

 189*5 x 1*32 = 262. The KI for each mixture is then calculated. 

 In the table the calculated and observed values are put side by 

 side, and it will be seen that there is a good agreement: — 



Percent. 



C IT PI • Percent. Percent, of Energy Pressure HI Rl 



2 3 ' of Gas. of Air. spent in Gas. in mm. Temp. observed, calculated. 



1 100 760 37 1985 — 



2 88o 1P5 945 421 87 5 253 259 



3 39-7 603 61 437 38 235 237 5 



4 17-3 827 33 433 38 220 220 



5 8-5 91-5 18 441 38-2 212 2105 



6 100 760 39 1985 — 



C.JFCl : 



1 100 760 32 200-5 



2 91-5 S-o 96 291 345 258 26<» 



8 35-3 647 56'5 310 36'5 232 235 



4 100 760 37 1985 — 



C.H, 



1 100 760 41 202 — 



2 835 16-5 95 321 43 262 264 



3 192 80-8 45-5 351 45 232 229 5 



4 100 760 45-6 195 — 



