160 SIR WILLIAM RAMSAY 



argon result from partial degradation of the radium 

 emanation (Trans. Chem. Soc. 1907, p. 1605). 



The search which Ramsay undertook later (Proc. Roy. 

 Soc. 81, p. 178) concerning the existence in the atmos- 

 phere of possible new members of the inactive series of 

 gases led to a negative result. With the aid of Mr. H. E. 

 Watson, who photographed the spectrum of the lighter 

 constituents of the air, and of Professor Richard B. 

 Moore, who investigated the less volatile portions of no 

 less than 120 tons of liquid air, no new constituent of 

 the atmosphere could be detected. But Ramsay 

 pointed out that there are gaps in the periodic table 

 which conceivably might be fitted by elements of the 

 inactive series having a higher atomic weight than that 

 of xenon. From the known gradation of properties 

 passing from helium to xenon it was certain that the 

 missing elements must be gases, and it was almost 

 equally certain that they would form no compounds. 



Three gases were known which are as inactive chemi- 

 cally as those of the argon group, but they disintegrate 

 during the process of separation. These were the eman- 

 ations from radium, thorium and actinium. Various 

 attempts to determine the atomic or molecular weights 

 of the emanations of radium and thorium led only to 

 an estimate for the emanation of radium as about 175. 

 Ramsay was, however, dissatisfied with the condition 

 of uncertainty *ifL which this interesting problem was 

 left in 1908. And soon afterwards he began a series 

 of experiments, with the assistance of Dr. Whytlaw Gray, 



