Relation between Uranium and Radium. 341 



intermediate between radium and its emanation were also 

 obtained. A freshly crystallized radium chloride appears to 

 suffer a slow augmentation in the rate o£ production of the 

 radium emanation, whereas a solution from which the radium 

 had been precipitated by sulphuric acid gave a progressively 

 diminishing rate. Still more recently Hahn and Meitner 

 (JPhys. Zeit. 1910, xi. p. 493) have observed a continuous 

 increase in the activity of a radium salt for many weeks after 

 the emanation has reached equilibrium, to a value more than 

 twice as great as the original equilibrium value, which they 

 regard as indicative of the existence of a radium X. So that 

 it is possible that the apparent variation of the sensitiveness 

 of the electroscope may admit of another explanation. 



However this may be, in view of the results obtained 

 during the past year with the uranium solutions, it is necessary 

 to withdraw the estimates of the period of the intermediate 

 parent of radium given in the last paper, and to treat the 

 results as affording data for the calculations of the minimum 

 period, but not as furnishing satistactory evidence so far of 

 the production of radium from uranium. I do not think 

 there is any doubt that a steady increase in the amount of 

 radium in all three solutions is taking place, but, as pointed 

 out in a previous paper, this may be explained by the possible 

 presence from the start of a minute quantity of the long-lived 

 parent of radium which I have shown is present in com- 

 mercial uranium salts in quite easily detectable amount. 



With regard to the minimum period the solution containing 

 408 grams of uranium purified on 13/12/06 gives the most 

 definite results on this point. When last tested, three and a 

 half years from purification, it contained between 8 and 9 

 units of radium. Seven good measurements have been made 

 on this solution in the last two years, some of which were 

 detailed in the last paper. Even if it be assumed that initially 

 both radium and its parent were completely absent, which is 

 an unlikely supposition, and that the radium present now has 

 all actually been formed from the uranium in the three and 

 a half years, the period of the long-lived intermediate body, 

 supposing there is but one, must be between 37,500 and 

 33,300 years. There is thus little doubt that the estimates 

 in the last paper were too low, and that there are not as yet 

 sufficient data from which to set an upper limit to this period. 

 There are many reasons for thinking it may even be many 

 times the minimum period assigned, and some of these 

 reasons are discussed in the next two papers. 



It thus becomes a matter of considerable importance in the 

 present state of radioactivity to fix at least an upper limit 



