1!)12] 



on the Orp/in of Radivm. 



407 



In the meantime a cognate discovery of first importance was made 

 by Boltwood, in America, who proved that actinium preparations ob- 

 tained from uranium minerals, and initially free from radium, grow a 

 fresh crop of radium with lapse of time. The growth is not l)y any 

 means a very minute one as in my experiments, in which the growtli 

 can only be put beyond all doubt aftei- the lapse of years. The growth 

 of radium from constituents separated from minerals can be readily 

 detected and measured in a relatively short space of time. The curve 

 shown (Fig. 9) is taken from a paper by Keetnian (Jahr. lladioact. 

 Elektronik, 190!), vi. 270), who has worked upon this parent of radium 

 in Germany. Although the total (juantity of radium represented l»y 

 this curve is only nine millionths of a milligram, it is enormous com- 

 pared with that shown by the other diagram (Fig. 3), in which tlic 

 quantity of radium produced in a period about eight times longer is 



Fig. 



nearly a hundred times less. Further work on this parent of radium 

 proved that it was not actinium, but a new radio-element admixed with 

 it, which Jioitwood called ionium. It is radioactive, and its radia- 

 tion consists entirely of a-rays of very low range. The chemical 

 nature of this ionium is absolutely identical, so far as is known, with 

 tbat of thorium, and it cannot be separated from it. On the other 

 hand, it is easily separated from any mixture, however complex, by 

 adding a trace of thorium and separating and purifying the latter. It 

 is interesting to note that no less than three at least of the known 

 radio-elements— ionium, radiothorium,and uraniuni A"— are absolutely 

 identical in chemical properties with thorium. 'J'his complete simi- 

 larity with known elements is one of the features of the chemistry o\ 

 the radio-elements. . . 



Returning to the experiments with the uraniuni solutions purified 

 by ether, Fig. 10 shows the growth of radium therein. The three 



