of Radium and Uranium. 



19 



by assuming that what we now call nranium consists of 

 three radio-elements, a parent element and two isotopic 

 products in equilibrium, all emitting a-rays. But if 

 these are present in relative amounts of the same ap- 

 proximate order of magnitude (i. e., 100, 92, 92, etc.) 

 then the a-rays emitted by at least one of them would 

 have to be of exceedingly short range and small ionizing 

 power and the rate of change of this substance would 

 be excessively slow. It is not impossible, but it does not 

 seem probable, that ordinary uranium may consist of 

 what we know as U I and XJ II, both radio-elements in 

 the main line of descent, and. a third isotope which is a 

 product in the collateral actinium series. But the diffi- 

 culties here are not inconsiderable aside from the fact 

 that the existence of such an isotope is somewhat difficult 

 to imagine. If present in amounts proportional to the 

 actinium this product would have to emit comparatively 

 long range (7-2 cm.) a-particles and would therefore have 

 a very short life period. Such a conclusion does not 

 seem at all probable in the light of our present knowl- 

 edge. 



It is not impossible that the values accepted for the 

 ranges of the a-particles from uranium are considerably 

 in error and that this is the reason for the lack of agree- 

 ment between theory and experiment. But until some 

 more definite data have been obtained there seems to be 

 little justification for abstruse speculation on the genetic 

 relationship in the earlier stages of the uranium series. 



Summary. 



The relation of the activity of radium to the activity 

 of the uranium with which it is in radioactive equilibrium 

 has been redetermined. The results obtained indicate 

 that if the activity of uranium is taken as unity the 

 activity of the radium is equal to approximately 049. 



The total activity of uranium mixed with equilibrium 

 quantities of its disintegration products has been com- 

 pared with the activity of the uranium alone, and the 

 former has been found to be 4-73 times the latter. 



A critical examination has been made of the various 

 theories which have been proposed to explain the genesis 

 of radium and actinium from uranium. None of these 

 theories appears to satisfy the necessary requirements. 



