1918-19.] An Electron-Transference Hypothesis, etc. 219 
On the other hand, we assume that when a halogen atom is combined 
with a carbon atom in organic compounds of the type C /l H 2 «+ 1 C'l 1 if i s 
electro-negative, and hence its atomic refractivity is given by A_ v 
From equations 1*36 and 137 it follows that 
2A_ 1 -(A +1 + A_ 1 ) = A. 
A 
i: 
— e 
R 
1 
2E b 
R 
2 a 
" R_ 
2 dea 
TR 
1-49 
1-50 
since dc = eT and rib = a. 
Hence, if we neglect quantities of relative order 10~ 3 , we have 
T 
A-,— A +1 = 2N 0 W . —e 
and 
■+i 
A_j + A +1 E n 
Equations 1*49 and 150 show 
(a) Atomic refractivity of 2C1 or 2Br obtained from organic com- 
pounds > atomic refractivity of Cl 2 or Br 2 obtained from 
gaseous molecule Cl 2 or Br 2 . 
(b) Percentage difference will be of the order — x 100 per cent. = 3 per 
r fi/ 
cent, approx, if we take n = 35, which is the order of the atomic 
weight of chlorine. This is in accord with experimental 
evidence, which indicates that n is proportional to the atomic 
weight and is usually less than the atomic weight. 
The following experimental values for halogen elements are given in 
Brtihl’s paper in Zeitschrift fur physik. Ghemie, vol. vii, 1891, p. 25 and 
p. 179:— 
Value of molecular refractive index of gaseous chlorine = 11*54, i.e. Cl 2 . 
Value of molecular refractive index of gaseous bromine = 16'91, i.e. Br 2 . 
Value of twice atomic refractive index of chlorine obtained from 
organic compounds = 12 028. 
Value of twice atomic refractive index of bromine obtained from 
organic compounds = 17*726. 
In each case, therefore, we have a verification of the inequality (a). 
Also the percentage difference obtainable from equation 1*50 is 
12-028 
U '! 4 xl00 
12-028 
17-73-16-91 
17-73 
4 per cent, approx, in case of chlorine, and 
x 100 = 4-6 per cent, approx, in case of bromine. 
