Electric Origin of Molecular Attraction. 637 



(Wied. Ann. lii.), to test this theory in the simplest concrete 

 way, treats the dissociation of N 2 4 into 2N0 2 and of I 2 into 21 

 as the performance o£ work e 2 /r against electric force for each 

 molecule of jS" 2 4 or I 2 dissociated, r being the distance apart 

 of the charges % and \) which hold the two parts of JST 2 4 or 

 L together. Richarz, assuming 10' J0 to be the number of 

 molecules in a c. c. of gas at 0° C. and 1 atmo, and r to be 

 10 -8 , finds for e a value agreeing with that derived from 

 other sources. In order to make his results more definitely 

 comparable with those of this paper, I will carry out his 

 reckoning in the following manner: — Let p be the mass of 

 1 c. c. of H 2 at 0° C. and 1 atmo, then the number of mole- 

 cules in a c. c. of any gas under standard conditions is yit/2/i, 

 and the work of dissociating such a c. c. of N 2 4 is 



'2h ' r 2\h) r 2\h) M.V 



But if pis the density of the molecule m = 4,7rpr B l3, taking 

 r to be its radius, 



4 



3 



*~fG)m*-* 



W=25xl0 6 ergs, M = 92, 



p= 92/49 (Phil. Mag. [5] xxxix. p. 7). 

 ^=•0896 x 10- 3 , A/*=345 X 10~ 17 . 



.'. r=8'8xl0- 9 cm. 



We have followed the method of Richarz in identifying r, 

 the distance apart of the charges, with the radius of N 2 4 . 

 Strictly, according to our reasoning, the electrical work per 

 molecule e 2 jr ought to be written e 2 /s, and the previous 

 reasoning would give us an equation for r*/s. But the im- 

 portant point at present is that the distance apart of the 

 electric charges forming chemical valencies in molecules is 

 found to be of the same order of magnitude as molecular 

 diameters both from the electric theory of molecular attrac- 

 tion and from the simple cases to which Helmholtz's electric 

 theory of chemical forces has been applied. Of course 

 Bicharz's simplifying assumptions require that when N 2 4 is 

 dissociated into 2N0 2 the mass of gas should consist of a 

 mixture of N0 2 ions, namely £X0 2 and [?N0 2 evenly mixed 

 and foruiing a conductor for any difference of potential. In 

 the same way, when iodine is dissociated to the atomic state 

 it ought to be a good conductor of electricity if Richarz's 

 calculation applies to it. Now J. J. '1 homson's experiments 

 on the passage of electricity through hot gases (Phil. JVIag. 

 [5] xxix.) proved that the specific conductivity of gaseous 



