300 Wellisch — Experiments on Active Deposit of Radium. 



separation of G and Q as far as diffusion effects are concerned 

 is merely an application of the undoubted principle that in 

 diffusion processes we may treat any large number of atoms 

 chosen at random as a separate gas to which the laws of dif- 

 fusion may be applied. Finally there is the most important 

 assumption that the activity in the gas is entirely neutral. In 

 order that this should be the case it is necessary, as explained 

 in the previous section, that the experiments should be per- 

 formed with small amounts of emanation ; all the deposit 

 particles in the gas appeared to have lost their charge when the 

 saturation current fell below 10" 9 ampere. The method of put- 

 ting this point to experimental test was to perform the three ex- 

 periments with various amounts of emanation in the testing 

 vessel ; if «, h and c remained in constant proportion over the 

 series this was taken to imply the absence of any appreciable 

 quantity of charged gas activity because it has already been 

 shown that the amount of charged activity decreased extremely 

 rapidly with decreasing amounts of emanation. The fact that 

 we are thus restricted to the use of small quantities of emana- 

 tion means of necessity an extremely small value for the activ- 

 ity in the first experiment in which the chief contribution comes 

 from the gas activity ; on this account every precaution was 

 taken in measuring the corresponding ionization current, the 

 electrostatic shielding being made thorough and the measuring 

 vessel preserved carefully from radio-active contamination. 



A very large number of experiments were performed to 

 obtain the ratios a : b : o. There was little difficulty in getting 



an accurate determination of the value - ; this came out 1/9 for 

 practically all the experiments. The most accurate determina- 

 tion of the ratio — is 1/20 ; this was obtained about 8 times 



under favorable measuring conditions. Still the ratio 1/15 was 

 obtained on a few occasions; of course there was always the 

 possibility in these instances of the presence in the gas of 

 charged deposit, but the amount of emanation was as always 

 quite small. The ratio was never less than 1/24. The value 

 of j> was taken as *83 ; this value represents the fraction of the 

 active deposit that settles on the cathode when 160 volts is 

 applied to the case, the quantity of emanation being supposed 

 to be so small that volume recombination is absent (v. Section 

 4). The value of f was taken as -10, this value representing 

 the fraction of the deposit that settles on the central rod in the 

 absence of an electric Held (v. Section 3). It was ascertained 

 experimentally that the exposure of one minute afforded ample 

 time for this fraction to reach the central rod. 



