' Various Gases by the a Particle* of Radium. 339 



The latter decreases rapidly as pressure is lowered. This has 

 been shown by Kleeman and myself (" On the Recombination 

 •of Ions, &c"). But when the alteration in density occasioned 

 by a rise uf temperature has been allowed for, there appears 

 to remain only a slight diminution in initial recombination, 

 which can be ascribed to the direct result of the increase 

 in temperature. This is shown with some clearness in some 

 .•experiments which I have made with C0 2 . They may 

 be tabulated as follows, the ionization at an electric force of 

 1000 volts per cm. being taken as 100: — 



Ionization Ionization Ionization 



at at at 



CO . 100° v o!t3 333 volts 166 volts 



per cm. per cm. per cm. 



(a) Pressure, 651 mm., 20° C. . . 100-0 95-0 90-2 



(I) Pressure, 760 mm., 72° C. .. 100-0 96-8 94-0 



A repetition of the experiment gave practically the same 

 result. The pressures and temperatures were so arranged that 

 the density was the same in each experiment. 



I also tried the experiment with ethyl chloride, but the 

 results were not so definite ; that is to say, change of tempe- 

 rature produced no very obvious effect. 



It is further assumed that the curves for different gases are 

 of the same form; in other words, that the function f(v) is 

 the same for all gases. 



A complete test of this hypothesis would require an accurate 

 delineation of the ionization curve in the case of each gas. 

 As has already been said, this would be a difficult task, in- 

 clusive, indeed, of our present purpose. But a comparison of 

 the curves in different gases, so far as they have been obtained, 

 shows that the principle is at least approximately true. For 

 example, the ratio of the range of RaC to that of RaA is the 

 same in all gases within errors of experiment, and again the 

 ratio of the maximum abscissa of the RaC curve to the abscissa 

 I is also constant, so far as I have measured it. As examples 

 of the constancy of the first of these two ratios, I have at 

 different times found it to be 1'16 in air, 1*47 in pentane, 

 1*17 in ethyl chloride, I'll in carbon dioxide, 1*18 in ethyl 

 alcohol, and 1'19 in ethylene. The differences here are probably 

 experimental only. As regards the second ratio, I have found 

 it to be 1*36 in air, 1*37 in ether, I'll in ethylene, 1*35 and 

 again I'll in ethyl chloride. This ratio is much more liable 

 to error than the former : for all ionizations are harder to 

 measure correctly than ranges, and the peak of the ionization 

 curve is an especially uncertain point. Also there is a special 



2B2 



