772 Mr. F. Soddy on the Production 



employed was one of home manufacture, and was only one- 

 eighth of the magnifying power of that used in the final 

 series of observations. These rates of leak have therefore 

 been multiplied by eight to make them comparable with the 

 later measurements. After blowing the air from the uranium 

 solution into the electroscope, the rate of leak was increased 

 from 0*048 division per minute (natural leak) to 0*136 

 division per minute. This is so small compared with the 

 rates of leak ultimately obtained that it may be neglected. 

 It represents less than 10" ll gram of radium. 



Observations were taken occasionally over a period of 

 eighteen months, and indicated a gradual growth of emanating 

 power of the uranium solution. But, owing to the disturbing- 

 effects of the radium employed in other researches in the 

 laboratory, the intermediate series of observations only possess 

 a qualitative value. The final series was carried out in 

 December 1904 and January 1905, in the newly erected 

 chemical laboratory at the Glasgow University, before any 

 radium had been introduced into the building. The first 

 test was made on December 17th, 1904, the air not having 

 been blown out of the bottle for nine months. An increase 

 of the rate of leak of the instrument from 1*56 divisions per 

 minute (natural leak) to 16*7 divisions per minute was 

 obtained. Thus, after a period of about 500 days, the rate of 

 leak due to accumulation of the emanation in the uranium 

 solution was over a hundred times greater than that initially 

 observed. 



II. — The emanation from the uranium solution comported 

 itself in all respects like the radium emanation, and there 

 can be no doubt that the emanation resulted from radium 

 produced from the uranium. The radium emanation when 

 newly admitted into an electroscope, owing to the production 

 of the excited activity, gives a rate of leak which steadily 

 rises over the first five minutes and then remains comparatively 

 steady during the next five minutes. If the emanation is 

 then blown or sucked out and the rate of leak immediately 

 tested, it will be found to be roughly equal to the amount by 

 which the initial rate of leak increased. In the course of a 

 few minutes after the removal of the emanation the rate of 

 leak of the electroscope becomes very small, if the emanation 

 has remained in the instrument only a few minutes. The 

 actual measurements recorded in the test of the air from the 

 uranium-nitrate solution on Dec. 17th 1904, are here given 

 as a fairly typical example of what was always observed. 



