286 Wells & Foote — One Hundred Years of Chemistry. 



We owe much of our knowledge of the radioactive 

 transformations to the researches of Rutherford and of 

 Soddy, and of their co-workers, but one of the important 

 products of the transformation of uranium, an element 

 which he called ionium, was characterized by Boltwood of 

 Yale (25, 365, 1908). 



Eadium and niton, apart from their radioactive prop- 

 erties, resemble barium and the inert gases of the atmos- 

 phere, respectively. The rates at which their progeni- 

 tors produce them, and the rates at which they themselves 

 decompose, bring about a state of equilibrium after a 

 time. Therefore a given amount of uranium, which 

 decomposes exceedingly slowly, can yield even after 

 thousands of years only a very small proportional 

 quantity of undecomposed radium, one-half of which 

 disappears in about 2500 years, because the amount 

 decomposed must eventually be equal to the amount pro- 

 duced. The first conclusive evidence that radium is a 

 product of the decomposition of uranium was given by 

 Boltwood in this Journal (18, 97, 1904). He found that 

 all uranium minerals contain radium; and the amount 

 of radium present is always proportional to the amount 

 of uranium, which shows the genetic relation between 

 the two. 



In the case of niton, which is produced by radium, and 

 is called also the radium emanation, the rate of decay is 

 rapid, so that if the gas is expelled from radium by heat- 

 ing, equilibrium is reached after a few days, with the 

 accumulation of the largest possible amount of niton. 



The conclusion has been reached by Rutherford and 

 others that the final product besides helium, in the radio- 

 active transformations, is lead, or at least an element 

 or elements resembling lead to such a degree that no 

 separation of them by chemical means is possible. 

 Atomic weight determinations by Richards and others 

 have shown that specimens of lead found in radioactive 

 minerals give distinctly different atomic weights from 

 that of ordinary lead. This fact has led to the view that 

 possibly the atoms of the elements are not all of the same 

 weight, but vary within certain limits — a view that is 

 contrary to previous conclusions derived from the uni- 

 formity in atomic weights obtained with material from 

 many different sources. 



The results of the investigations upon radioactivity 



