220 
Proceedings of the Royal Society of Edinburgh. [Sess. 
These results are in agreement, so far as order of magnitude is concerned, 
with the result ( b ). 
These results are derived on the assumption that the additive law, 
without correction for contributions due to atomic interaction, can be 
applied. This is so in the case of organic compounds which contain a 
carbon chain and have no double bindings in their constitution, and also 
in the case of inorganic compounds which do not display great chemical 
activity when acted upon by electrical fields of force. Gaseous halogen 
is quite stable when acted upon by electrical fields of force, and so we have 
good reason to assume that the additive law for atomic refractivities holds 
in this case very closely. The values of the atomic refractivity of chlorine 
and bromine deduced from organic compounds are used as a basis for the 
determination of the chemical constitution of organic compounds, and the 
results obtained are very satisfactory. 
(i) It is now proposed to discuss the difference in value between the 
atomic refractivity of an element according as it plays an electro-positive 
or electro-negative part in a molecule. 
When the atom plays an electro-positive part its atomic refractivity 
is A +s , and when it plays an electro-negative part its atomic refractivity is 
indicated by A_ & . 
We have the relation at once that 
S -f- lb ^ S . 
From equations 1*36 and T37 we have 
A a WK » T 
“* +s P R 
t? i 7 / 7 7 , Tp \ kb i. -)- clc tp , / j -[t* \ ctc> 
E + ke - (kd + E) — — — - E + se + (sd - E)- 
RT 
-rp b . / 7 \ &T GCL 
e - E E + ( S -%_- s 
RT 
1-51 
1-52 
= — (k + s)e[l + (s - k ) . h . 10" 2 ] neglecting E^ and ^ 
pK R R 
A A wnj /7 n 
. . \ A_ fc - A+g = ^ (k + s)e approx. 
A_ fc A +s k + s 
1 — Jc 
These equations show 
(а) 
(б) 
n + k 
A _ ]c > A +s . 
Percentage difference = x 100 . 
n + k 
It is difficult to obtain experimental results sufficiently trustworthy to 
confute or to support the above results, as the change in the nature of the 
binding may change the electrical configuration of a molecule. 
