1012] 



on the Ori[/m of Radium. 



409 



so far, the radiain formed is derived, not from the uranium, but from 

 varying iutinitesimal quantities of ionium still unremoved by the 

 purification processes. 



Taking No. Ill as the best of the first batch of preparations, the 

 growth of radium therein is only about ^oooo P^^'t of what would 

 have occurred if uranium were the direct parent of radium. Some 

 idea of the minuteness of the quantities of radium indicated by these 

 curves can be got by the following consideration. Radium bromide 

 at its present price costs about 16/. per milligram. For the element, 

 radium, this is at the rate of 750,000?. per ounce. The diagram 

 (Fig. 10) is 2 feet high. To represent a pennyworth of radium on 



Fig. 10. 



this scale would require a diagram over 6000 feet high, whereas to 

 represent Keetman's curve (Fig. 9) would require one as high as 

 St. Paul's Cathedral. 



These results, therefore, confirm absolutely the view that uranium 

 does not produce radium directly. As Rutherford first showed, if 

 ionium is the only long-lived radio-element between uranium and 

 radium, the growth of radium from uranium must initially be pro- 

 portional to the square of the time, and should be represented by the 

 equation R = 6 X 10~*AT^, where R is the radium formed per 

 kilogram of uranium, T is the time in years and 1/A is the period of 



