32 Professor Ernest Piutherford [Jan. 31, 



has been completely substantiated by the independent work of 

 Boltwood, Striitt, and McCoy. It has been shown that the quantity 

 of uranium corresponding to 1 gram of radium is 3*8 x 10 ~' grana, 

 and is the same for minerals obtained from all parts of the world. 

 Since the radium is always distributed throughout the mass of 

 uranium, we cannot expect to find nuggets of radium like nuggets 

 of gold, unless by some chance the radium has been dissolved out of 

 radio-active minerals and redeposited within the last few thousands 

 of years. To those who had faith in the distintegration theory, this 

 unique constant relation between the amounts of two elements was a 

 satisfactory proof that radium stood in a genetic relation with 

 uranium. A search was then made for the unknown intervening 

 product wliich, if isolated, must grow radium at a rapid rate. A year 

 or so ago Boltwood observed that a preparation of actinium separated 

 from a uranium mineral did grow radium at a constant but rapid 

 rate. It thus appeared as if actinium were the long-looked-for parent 

 of radium, and that actinium and its long family of products inter- 

 vened between uranium X and radium. I was, however, able to show 

 that actinium itself was not responsible for the growth of radium, but 

 another unknown substance separated with it. These results were 

 confirmed by Boltwood, who finally succeeded in isolating a new 

 substance from uranium minerals, which was slowly transformed into 

 radium. This substance, which he termed " ionium,"' has apparently 

 chemical properties similar to those of thorium, and emits a rays of 

 penetrating power less than those of uranium. 



The main previsions of the theory have thus been experimentally 

 verified. Radium is a changing substance the amount of which is 

 kept up by the disintegration of another element, ionium. In order 

 to complete the chain of evidence, we require to show that uranium 

 grows ionium, and it is probable that evidence in this direction will 

 soon be forthcoming. We thus see that we are able to link uranium, 

 ionium, radium, and its long line of descendants, into one family, 

 with uraniimi as its first parent. As uranium has a period of trans- 

 formation of more than one thousand million years, it will not be 

 profitable at the moment to try and trace back the family further. 



It appears almost certain that, from the radio-active point of 

 view, uranium and thorium must be considered as two independent 

 elements. The case of actinium is difiPerent, for Boltwood has shown 

 that the amount of actinium in minerals, like the amount of radium, 

 is proportional to the amount of uranium. This indicates that 

 actinium stands in a genetic relation with uranium. Unless our 

 experimental evidence is at fault, it does not appear probable that 

 actinium belongs to the main line of descent of uranium, for the 

 activity of actinium separated from a mineral compared with radium 

 is only about one-quarter of what we should expect under such con- 

 ditions. I think that a suggestion Avhich I put forward some time 

 ago may account for the obvious connection of actinium with 



