Mass-Spectra of Chemical Elements. 625 



are relatively distant from each other. This is certainly the 

 case when the molecules H 2 and H 3 are formed from H 1; so 

 that their masses will be two and three times the mass of Hx 

 with gre^.t exactness. (It must be remembered here that the 

 masses given by these experiments are those of positively 

 charged particles, E^ being presumably a single particle of 

 positive electricity itself, and that the mass of an electron on 

 the scale used is "00054 and too small to affect the results.) 



In the case of helium, the standard oxygen, and all other 

 elements, this is no longer the case ; for the nuclei of these 

 are composed of particles and electrons packed exceedingly 

 close together. Tire mass of these structures will not be 

 exactly the sum of the masses of their constituents but 

 probably less, so that the unit of mass on the scale chosen 

 will be less than that of a single hydrogen atom. 



The Heavier Elements. 



The results hold out the probability of great complexity 

 in elements of high atomic number, which has already been 

 proved by entirely different methods in the case of lead. The 

 present apparatus has a resolution factor too low to deal 

 adequately with these ; so attention is being given to 

 elements within its scope and to which the analysis can 

 be applied. Besults are steadily accumulating, which will 

 be published in due course. 



In conclusion the author wishes to express his indebtedness 

 to the Government Grant Committee of the Royal Society 

 for defraying the cost of some of the apparatus employed. 



Summary. 



A positive ray spectrograph capable of giving a focussed 

 mass-spectrum is fully described in detail and its technique 

 explained. 



The results of a provisional analysis of eleven chemical 

 elements — H, He, C, N, 0,Ne, CI, A, Kr, X, Hg — are given, 

 showing that of these the first five only are " pure," the others 

 being apparently composed of various numbers of isotopic 

 constituents, krypton containing no less than six. 



With the exception of those due to H 1; H 2 , and H 3 , all 

 masses measured, allowing for multiple charges, are exactly 

 whole numbers within the error of experiment (0 = 16). 



The lines due to hydrogen indicate that the mass of the 

 atom of this element is greater than unity on this scale and 

 in good agreement with the chemical value 1*008. Reasons 

 for this are suggested. 



Cavendish Laboratory, 

 March 1920. 



