Mass-Spectra of Chemical Elements. 623 



Krypton (At. Wt. 82-92) and Xenon (At. Wt, 130-2). 



The results with these elements were particularly inter- 

 esting. The only source available, for which the author is 

 indebted to Sir J. J. Thomson, was the remains o£ two small 

 samples of gas from evaporated liquid air kindly supplied by 

 Sir James Dewar some years ago for examination by the 

 " parabola " method. Both samples contained nitrogen, 

 oxygen, argon, and krypton, but xenon was only detected in 

 one and its percentage in that must have been quite minute. 

 Krypton is characterized by a remarkable group of five strong- 

 lines at 80, 82, 83, 84, 86, and a faint sixth at 78. This group 

 or cluster of isotopes is beautifully reproduced with the same 

 relative values of intensity in the second, and fainter still in 

 the third order. These multiply-charged clusters give most 

 reliable values of mass, as the second order can be compared 

 with A (40) and the third with CO or N 2 (28) with the highest 

 accuracy. It will be noted that one member of each group 

 is obliterated by the reference line, but not the same one. 

 The singly and doubly charged krypton clusters can be seen 

 to the right and left of Spectrum VIII. It will be noticed 

 that krypton is the first element examined which shows 

 unmistakable isotopes differing by one unit only. 



On the krypton plates taken with the greatest magnetic 

 field faint, but unmistakable indications of lines in the region 

 of 130 could just be detected. The richest sample was therefore 

 fractionated over liquid air, and the last fraction, a few cubic 

 millimetres, 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 filial 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 vapour (which is 

 generally beneficial 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 or! decreasing intensity around points cor- 

 responding 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. 



