128 CONCEPTION OF THE CHEMICAL ELEMENT 



always, as it did with radium, imply unique chemical 

 and spectroscope character. The new members 

 resembled known elements in chemical character so 

 closely that they could not be separated from them 

 by chemical analysis, although sharply differentiated 

 from them by the radioactive properties. Radiolead, 

 or radium-Z>, cannot be separated from the lead 

 which, being- a product of uranium, accompanies it 

 always in uranium minerals. Ionium, the direct 

 parent of radium, cannot be separated from thorium ; 

 but the most instructive case, historically, which 

 shows well how the new method of radioactive 

 analysis serves to distinguish different elements, 

 where chemical analysis fails, was the case of 

 radiothorium. 



CHEMICALLY NON-SEPARABLE ELEMENTS. 

 Ramsay and Hahn, in the course of working up a 

 large quantity of thorianite for radium, observed in 

 fractionating the radium from the barium in the 

 usual way that the activity of the material concen- 

 trated at both ends of the fractionation. The activity 

 accumulating in the more soluble fractions was due 

 to a new product, which they termed radiothorium. 

 It produces thorium-^", the thorium emanation, 

 etc., in successive changes. Naturally enough, they 

 thought they had separated radiothorium by chemical 

 processes from thorium, but they had not, for that, 

 as we know, is quite impossible. Then Hahn found 

 along with the other end fraction, containing the 

 radium, a further new product, mesothorium, which 

 is intermediate between thorium and radiothorium. 

 The radiothorium they had separated from thorianite 

 was not that present in the mineral when they started, 

 but that which had re-formed from the mesothorium 

 after it had been separated from the thorium in the 

 mineral. Could any more elegant extension, not 



