The Mass Spectra 'of Chemical Elements. 141 



element having a different atomic number, i.e., is an Isobare. 

 The latter are known to exist among radioactive elements, 

 but none have so far been discovered during the work on 

 mass spectra. 



Iodine (At. Wt. 126*92). 



The results with this element were fortunately both 

 definite and conclusive. Methyl iodide was employed, its 

 vapour being introduced mixed with C0 2 and CH 4 . It gave 

 one strong line at 127 satisfactorilv confirmed bv another 

 single line at 142 due to CH 3 L "Spectrum I. "(Pl.VIl.) 

 shows the former, but the latter is too faint to reproduce well. 



This proves iodine to be a simple element in an unequivocal 

 manner, a rather unexpected result since all the speculative 

 theories of element evolution, by Van den Broek and others, 

 predict a complex iodine. Kolhweiler {Zeit. Plujs. Chem. 

 1920, xcv. pp. 95-125) not only deduces from theory five 

 isotopes of iodine of weights 122, 124, 126, 128, 130, bur, 

 also claims to have achieved a considerable separation of 

 them by diffusion. 



Antimony (At. Wt. 120'2). 



Antimony hydride SbH 3 was used. This was made by 

 dissolving antimony magnesium alloy in dilute acid. Unlike 

 the corresponding arsenic compound it gave an entirely 

 negative result, no line whatever being distinguishable in 

 the region expected from the atomic weight. This failure is 

 probably to be ascribed to the exceedingly unstable nature of 

 the antimony compound. 



Tin (At. Wt. 118*7). 



Tin tetrachloride was employed in the investigation of this 

 element. The vapour of this compound attacks the tap 

 grease used in the apparatus, which makes it extremely 

 difficult to deal with. The results were entirely negative 

 except in one case. On this occasion a second attempt to 

 get the selenium line from selenium hydride was actually in 

 progress, but a good deal of SnCl 4 vapour had been intro- 

 duced previously, and the chlorine lines were so intense that 

 some " resurrected " compound of chlorine must have been 

 the principal factor in the discharge. For some unknown 

 reason the discharge tube was working abnormally well. 

 On one of the spectra then obtained, Spectrum II., a group 

 of lines of even integral mass 116, 118, 120, 122, 124 

 (followed by iodine 127) could be distinguished and some o^ 



