MASS SPECTRA OF THE ELEMENTS ASTON. 



239 



be detected. The richest sample was therefore fractionated over 

 liquid air, and the last fraction, a few cubic millimeters, was just 

 sufficient to produce the xenon lines in an unmistakable manner. 

 These can be seen on Spectrum IX, but are somewhat fuzzy owing 

 to the wide diaphragm used to get maximum intensity. They are 

 apparently five in number and appear to follow the integer rule. 

 Until pure xenon is available no final figures can be given, but the 

 values may be taken provisionally as 128, 130, 131, 133, and 135. 



MERCURY (AT. WT. 200.6). 



Owing to the presence of mercury vapor (which is generally bene- 

 ficial to the smooth running of the discharge) the multiply-charged 

 particles of this element appear on nearly all the plates taken. They 

 appear as a series of blurred clusters of decreasing intensity around 

 points corresponding to 200, 100, 66.6, 50 * * * etc., some of 

 which are indicated in the spectra reproduced. It may be stated 

 provisionally that they indicate a strong component 202, a weak one 

 204, and a strong band from 197 to 200 containing three or four more 

 unresolvable at present. 



Table of results obtained to December, 1920. 



(Numbers in parentheses are provisional only.) 



THE WHOLE-NUMBER RULE. 



The most important generalization yielded by these experiments 

 is the remarkable fact that (with the exception of H 15 H 2 , and H 3 ) 

 all masses, atomic or molecular, element or compound, so far meas- 

 ured, are whole numbers within the accuracy of experiment. It is 

 naturally premature to state that this relation is true for all elements, 



