﻿the Active Deposit of Radium in an Electric Field, 12?j 



The agreement is only rough, and further experiments 

 will be necessary at these small potentials. 



The percentage cathode activity increases so slowly with 

 the higher potentials applied that it appeared as if some 

 definite fraction of the activity was always bound to be 

 deposited on the case. Subsequent experiments made with 

 large potentials obtained by using the Wimshurst machine 

 showed, however, that the percentage cathode activity con- 

 tinually increased with the potential. It is not out of place 

 to mention briefly here two sets of experiments which were 

 conducted prior to the use of the Wimshurst machine. 



It was suggested that, if a large uniform electric field 

 were applied, possibly the number of uncharged carriers 

 might become insignificant. For this purpose the emanation 

 was introduced into a vessel consisting of two parallel elec- 

 trodes of aluminium (each 58 mm. in diameter) insulated by 

 an ebonite ring 20 mm. thick; the vessel contained air at a 

 pressure of 1 atmosphere. Experiments made with applied 

 potentials of 160 and 1000 volts gave values of 75 and 82-6 

 respectively for the percentage of positively charged curriers. 



The second set of experiments had as object to determine 

 whether RaA was deposited on the case. To test this point 

 the cylindrical vessels were employed as usual and large 

 potentials applied, but exposures of only 1 minute duration 

 were made. It was found that the resulting curve of dec;iy 

 of the case activity had the characteristic properties of the 

 curves of decay for the activity due to a short exposure to 

 the radium emanation. 



Mention might also be briefly made here of some experk 

 ments which were performed to ascertain whether there was 

 any alteration in value of the percentage cathode activity 

 resulting from a long exposure with large positive potentials, 

 applied to the case when throughout the exposure the ioniza^. 

 tion current was greatly increased by the passage of Kontgen 

 lays through the vessel. The alteration, if any, was very 

 small and for the present, at any rate, we must assume that 

 the action of the Rontgen rays is without effect on the dis- 

 tribution of the activity. 



5. Experiments with Air at Reduced Pressure, 



The experimental results described in the preceding section 

 strongly suggest that over a wide range of potentials the 

 percentage oh' the total activity which is deposited on the case 

 represents the percentage lack of saturation of the positive 

 ionization current. These experiments related to the activity 

 distribution in air at a pressure of 1 atmosphere. Now 



o 15 2 



