CONSTITUTION AND TEMPERATURE ON MAGNETIC SUSCEPTIBILITY. 279 



that of the line H a , then the molecular diamagnetic susceptibility of hydrogen 

 ( 61'Ox 10" 7 ) can be accounted for, and each electron orbit of radius 10~ 8 cm. has a 

 magnetic moment + 16'3 x 10" 22 , nearly equal to that of the magneton, + 18'5 x 10" 22 . 

 The atomic susceptibility of carbon in combination is shown by PASCAL to be 



62'5 x 10~ 7 , and in connexion with the additive law this value is consistent with the 

 experimental values of the molecular susceptibilities. The mean experimental value 

 of the atomic susceptibility of diamond is 59'0x 10~ 7 .* The mean of these values 

 is 607 x 10~ 7 , which is probably as accurate a value as is available at present. But 

 this value is almost exactly twice that of the atomic susceptibility of hydrogen 



30'5x 10~ 7 . Probably therefore the atom of carbon contains two magnetons. As to 

 the period of revolution we have 



M = %. e . M S = ^ 



T 



where 



M = moment of orbit, 



e = electron charge in e.m.u., 

 r = radius of orbit, 

 T = period, 



and this implies that the period T for the carbon atom is not equal to that of the line 

 H a unless r = 10~ 8 for the carbon atom. 



The sum of the atomic susceptibilities of the atoms in the group (JrL is 



-123 'ox U)- 7 . 



Experimentally, PASCAL showed that the difference of molecular susceptibility in a 

 number of compounds whose constitution differed by this group was 



-1 187x 10- 7 . 



The mean of these two values is 121 '1 x 10~ 7 which is probably very near the true 

 value. But this is almost exactly four times the value of the atomic susceptibility of 

 hydrogen, viz., 30'5xlO~ 7 , and in this combination, CH 2 , we may say that each 

 hydrogen atom has one magneton and the carbon atom has two magnetons. 



An ethylene linkage, according to PASCAL, lowers the diamagnetic molecular 

 susceptibility of the compound by +57 x 10~ 7 , while two or more such linkages lower 

 it by + 110 x 10~ 7 . These values are respectively nearly equal to twice and four times 

 the atomic susceptibility of hydrogen. 



As the additive law holds in the case of the simpler liquid hydrocarbons, it will hold 

 for all the others which differ only by CH 2 groups, and therefore, taking the values of 

 X into account, any member of the three homologous series 



* HONDA, 'Ann. der Phys.,' vol. 32, p. 1044, 1910, gives -59-5xlQ- 7 ; OWEN, 'Ann. der Phys.,' 

 vol. 37, p. 693, 1912, gives -58'5x 1Q- 7 . 



VOL. CCXX. A. 2 Q 



