Deposit of Radium in an Electric Field. 447 



upon the duration of the exposure, provided that sufficient 

 time was given the gas activity to accumulate before the 

 exposure. Thus, the activity of the electrode after an 

 exposure of 1 minute was found to be nearly the same as in 

 case of a long exposure, showing that practically the whole 

 amount of the active matter was suspended in the gas. 



It seemed to be of interest to investigate also the time 

 necessary for the electric wind to carry the whole amount of 

 the activity suspended in the gas towards the electrodes. It 

 was found that during the first few seconds of exposure the 

 greatest part of the gas activity is deposited on the electrodes, 

 while an exposure of 30 seconds is enough to remove com- 

 pletely the gas activity from the emanation. 



On the Rate of Recombination of Radioactive Ions. 



11. It is clear from the above results that the question of 

 the distribution of active deposit of radium in an electric 

 field is closely connected with the rate cf recombination of 

 the recoil atoms, since only the uncharged carriers of active 

 matter are carried to the electrodes by the electric wind. 

 It has been shown in sec. 5 that even with very small quan- 

 tities of emanation and large potential differences applied 

 between the electrodes, the anode activity still remains of the 

 order of 10 per cent, of the cathode activity. Since only 

 one half of the uncharged recoil atoms is carried by the 

 electric wind to the anode, we must suppose that not less 

 than 20 per cent, of the recoil atoms from the emanation 

 are neutral under these conditions. This could be easily 

 explained by suggesting a large columnar recombination of 

 the recoil atoms due io their ionizing power in the beginning 

 of their path ; but further considerations show that the volume 

 recombination of the radioactive ions must also be large com- 

 pared with that of ordinal gaseous ions. Thus, when the 

 electrodes are exposed to emanation in the presence of a 

 strong additional source of ionization (see sec. 5), the anode 

 activity is always equal to the cathode activity, showing that 

 practically all the recoil atoms have lost their charge by 

 recombination; while, so far as ordinary ions are concerned, 

 the same potential difference established between the elec- 

 trodes produces nearly a saturation current. Further, if a 

 strong source of ionization be introduced into the condenser 

 AB (fig. 1), the activity carried by the electric wind to the 

 plate D may reach the value of 60 per cent, of the total 

 amount of active matter projected by recoil from the active 

 surface of the disk R, which shows that a greater part of the 



