770 Mr. F. Soddy on the Production 



period before a decisive result is attained. The experiments 

 here described were started in May 1903. At first only 

 negative results were obtained, but later, after a kilogram of 

 uranium nitrate had been kept under observation for a period 

 of eighteen months, undeniable evidence of a positive character 

 was obtained, although a much slower rate of production of 

 radium from uranium was indicated than was to be expected 

 if a direct change of uranium or uranium X into radium 

 occurred. These two results were briefly announced in 

 letters to ' Nature ' (Mav 12th, 1904, and January 26th, 1905). 

 Whetham (' Nature/ May 5th, 1904, and Feb. 2nd, 1905) 

 has given the result of some experiments undertaken on the 

 same problem, and was able to confirm the positive result 

 announced in the second letter. 



During the progress of these investigations, the problem 

 has been attacked by a different method by other investigators, 

 to whose work some reference will be made later in the paper. 

 The method is based upon the accurate determination of the 

 ratio of relative quantities of uranium and radium in a large 

 number of minerals, to see whether the requirement that the 

 two elements always exist in a fixed relative proportion is 

 fulfilled. 



Radium is distinguished from uranium in giving a relatively 

 short-lived gaseous disintegration product or emanation, 

 which is characterized by certain well-marked peculiarities. 

 The emanation may therefore be used as a qualitative test 

 for the presence of radium. Since the laws regulating the 

 rate of production and accumulation of this emanation are 

 well known (Rutherford & Soddy, Phil. Mag. [6] v. 1903, 

 p. 450), the amount of emanation accumulating in a known 

 time can be used as a quantitative measure of the amount of 

 radium present. The research divides itself into four sections. 

 In the first place it will be shown that a quantity of uranium 

 originally practically free from radium, and possessing there- 

 fore no power of producing an emanation, after being kept a 

 certain time in a closed bottle develops an unmistakeable 

 though still small emanating power. Secondly, the character- 

 istics of the emanation produced will be shown to conform to 

 those of the radium emanation. Thirdly, experiments will 

 be given in which the quantity of emanation produced from 

 the uranium was compared with the quantity produced from 

 a known weight of radium, and the amount of radium finally 

 present in the uranium deduced. Lastly, the probable cause 

 of the slow rate of production will be considered. 



