Mass Spectra of Chemical Elements. 143 



than the normal ones, but chemically they are of great in- 

 terest (v. Sir J. J. Thomson, ' Rays of Positive Electricity ') 

 and provide a means of deciding conclusively which of the 

 four strong lines 35, 36, 37, 38, always produced when 

 chlorine is present, are really due to isotopes of that element.. 

 On the negative mass spectra of chlorine obtained in this 

 way only two of these lines 35 and 37 could be distinguished. 

 It is, therefore, perfectly certain that 36 and 38 are not to 

 any reasonable extent due to isotopes of chlorine, which is a 

 very "valuable confirmation of the explanation already sug- 

 gested (/. c. p. 620). 



The line 39 would not have been intense enough to appear 

 on these negative mass spectra, so must still remain doubtful. 

 It is hoped, however, when the negative lines are investi- 

 gated more fully, that it will be possible to settle this point 

 also by their evidence. 



In conclusion the author wishes to repeat his acknow- 

 ledgment to the Government Grant Committee of the Royal 

 Society for part of the apparatus employed. 



Table of Elements and Isotopes. 



lement 



Atomic 

 Number. 



Atomic 

 Weight. 



Minimum 



number of 



Isotopes. 



Masses of Isotopes in- 

 order of intensity. 



h ...: 



1 



1-008 



1 



1-008 



He.... 



2 



399 



1 



4 



B .... 



5 



10-9 



2 



11, 10 



.... 



6 



12-00 



1 



12 



N ..., 



7 



1401 



1 



14 



..., 



8 



16-00 



1 



16 



F .... 



9 



19-00 



1 



19 



Ne .... 



10 



20-20 



2 



20, 22, (21) 



Si .... 



14 



28-3 



2 



28, 29, (30) 



P .... 



15 



31-04 



1 



31 



S .... 



16 



32-06 



1 



32 



CI ... 



17 



35-46 



2 



35, 37, (39) 



A .... 



18 



39-88 



2 



40, 36 



As .... 



33 



74-96 



1 



75 



Br .... 



35 



79-92 



2 



79,81 



Kr .... 



36 



82-92 



6 



84, 86, 82, 83, 80. 78 



I .... 



53 



126-92 



1 



127 



X ... 



54 



130-2 



5(7). 



129,132, 131,134.136. 

 (128), (130?) 



Hg... 



80 



200-6 



(6) 



(197-200), 202, 20 1 



(Numbers in brackets are provisional only). 



