Mass-Spectra of Chemical Element*. 631 



there no lines of lower order corresponding to t hese, the whole- 

 number rule mighl be in question ; lmt all doubt is removed 

 by the tact that the lines -47 and -19 are two of the strongest 

 on the plate. A comparison of several spectra upon which 

 these lines occur shows a definite intensity relation which 

 practically confirms the conclusion that the first pair of lines 

 are true second-order lines corresponding to the first-order 

 lines of the second pair. Now lines 47 and 49 cannot by 

 anv reasonable argument be elementary } they must in fact 

 be due to compounds of fluorine with boron B n F 2 or 

 silicon Si L> F, or due to both. Further evidence of the 

 capability of fluorine compounds to carry two charges is 

 offered by line 33*50, which is undoubtedly the second-order 

 line corresponding to 67, i. e. B ]0 F 3 or Si 29 F 2 . So far as 

 results go, fluorine appears to be unique in its power of 

 yielding doubly- charged molecules in sufficient number to 

 produce second-order lines of considerable strength. 



Bromine (At. Wt, 79-92). 



The results with this element were definite and easy to 

 interpret. Its chemical combining weight is known with 

 great certainty, and is very nearly the whole number 80. It 

 was rather a surprise, therefore, that it should give a mass- 

 spectrum which showed it to consist of a mixture of two 

 isutopes in practically equal proportions. Methyl bromide 

 was used for the experiments, and one of the results is 

 reproduced in Spectrum VI. The characteristic group con- 

 sists of four lines at 79, 80, 81, and $2. 79 and 81, appa- 

 rently of equal intensity, are much the stronger pair, and 

 are obviously due to elementary bromines. This result is 

 practically confirmed by second-order lines ;it 39*5 and 40*5 

 too faint to reproduce, but easily seen and measured on the 

 original negative. The fainter pair 80 and 82 are the 

 expected lines of the two corresponding hydrobromic acids. 

 The same difficulties as were discussed in the case of chlorine 

 in the previous paper prevent the attainment of absolute 

 certainty in determining the composition of bromine, or 

 indeed that of any element capable of forming hydrogen 

 compounds; but the conclusions stated above may be re- 

 garded as having a high degree of probability. 



Sulphur (At. Wt. 32-06). 



Spectra VII. and VI IT. -how the effect of the addition of 

 sulphur dioxide to the gas in the discharge- tube. Above 

 each is a comparison spectrum taken immediately before the 



