WORK ON RADIUM 163 



value of which may have been derived from other considera- 

 tions. In the present case these considerations are the result 

 of the disintegration theory. Determinations by Madame Curie 

 and by Thorpe of the atomic weight of radium show beyond all 

 doubt that it differs little from 226*4. That four atoms of helium 

 separate from one atom of radium is rendered almost certain 

 from the work of Dewar and from experiments by Rutherford 

 and by Ramsay and Soddy. That three atoms of helium are 

 lost by niton on decay has been shown in the preceding pages. 

 It follows that one helium atom must escape when radium 

 changes into its emanation ; hence the true atomic weight of 

 the emanation must be 222*4. This number hardly differs from 

 the mean of the atomic weight determinations given in this 

 paper ; and the disintegration theory receives a further con- 

 firmation." 



Ramsay's views as to the utilisation of radio-active 

 change to effect chemical decomposition and even 

 " transmutation " of elements, have already been re- 

 ferred to. His study of the emanation of radium, or 

 niton as he called it, led him to consider this problem 

 seriously and to make experiments; the results of which 

 are recorded in two papers * communicated to the 

 Chemical Society in 1907. The first of these commences 

 with the following remarks : 



" The emanation from radium is one of the most potent, if not 

 thejnost potent chemical agent which exists in nature. Of all 

 known substances it is endowed with the greatest content of 

 potential energy ; for one cubic centimetre contains, and can 

 evolve, nearly three million times as much heat as an equal 

 volume of a mixture of two volumes of hydrogen with one of 



1 Transactions (1907), p. 931, part i. ; Transactions (1907), p. 1593, 

 part ii. (Cameron and Ramsay). 



