Production and Origin of Radium. • 785 



important stage in the attack on this problem, for it clearly 

 shows that radium, as theory predicted, is produced from 

 another substance and that this parent substance is normally 

 present with actinium. 



Boltwood concluded that actinium was the direct parent 

 of radium and was itself an intermediate product between 

 uranium and radium. This conclusion was strongly sup- 

 ported by his observation that the amount of actinium in 

 minerals, like the amount of radium, was proportional to the 

 amount of uranium. Since actinium has probably a life 

 comparable with that of radium, such a conclusion is con- 

 sistent with the observed absence of growth of radium in 

 uranium solutions, for the uranium must first form a con- 

 siderable quantity of actinium before the transformation 

 product of the latter, viz. radium, could be detected in the 

 solution. This question will be discussed later in the paper 

 after the consideration of further experimental results. It 

 will be seen that the problem is more complicated than at 

 first appeared. 



§ 2. Old Experiments. 



It may be of interest to give a brief account of some ex- 

 periments commenced by myself in 1904 to determine whether 

 radium was continuously produced from actinium. A pre 

 liminary account of this work was given in the Bakerian 

 Lecture (Phil. Trans. A, p. 218, 1904). Two grams of an 

 active preparation^ of activity about 250 times that of uranium, 

 obtained from Giesel, were taken and dissolved in acid. The 

 initial content of radium was determined by the emanation 

 method, and the greater part of it then removed by succes- 

 sive precipitations in the solution of small quantities of barium 

 as sulphate. Measurements were then made of the amount 

 of radium in this solution at intervals over a space of three 

 months, but with no certain evidence of the growth of 

 radium. The amount of radium was estimated by the ema- 

 nation method. The radium emanation, which was allowed 

 to collect in the solution for a known interval, w T as removed 

 into a large electroscope by aspirating a considerable amount 

 of air through the solution. Later work of Boltwood has 

 shown that this aspiration method is unreliable for an accu- 

 rate determination of the amount of radium present, but it 

 no doubt serves for comparative measurements under identical 

 conditions. 



In the light of later knowledge, the method employed for 

 the separation of the radium present initially in the solution 



