TRANSACTIONS OF SECTION B. 491 
the halogen derivatives are plotted against the absolute temperatures, the points 
for the most part fall near the curve constructed for the paraffins, and represented 
by the formula A= dears The first value of A is decidedly low in each case 
T 0:0148./T 
(average deviation from curve 2°-7); the later ones are rather high in nearly 
every case (average deviation 0°86). Similar results are in general obtained 
with other homologous series of compounds in which molecular association is not 
believed to occur, but, as will be seen from the following table, the deviations 
from the normal paraffin curve are greater in the case of those series the lower 
members of which, according to Ramsay and Shields, are characterised by mole- 
cular association. 
In the great majority of cases the deviations are greatest for the lowest 
members of a series, the calculated values of A being almost invariably higher than 
the observed, and this may perhaps be explained in the manner suggested by 
Ramage. I have, therefore, divided each series into two groups, the first ending 
and the second beginning with the lowest member of the series which contains a 
CH, group linked to two carbon atoms. Thus, of the alkyl chlorides, the first 
group contains CH,Cl, CH,CH,Cl, and CH; —CH, — CH,Cl, and the second group 
begins with propyl chloride, so that all its members contain one or more C—CH,—-C 
roups. 
- Tk the case of the ethers, esters, and other compounds which contain two alkyl 
radicals, a series is regarded as homologous when one radical remains unaltered 
and the other increases by stages of CH,. The variable radical only is considered 
in dividing the series into the two groups; thus, although propionic acid contains 
a ©—CH,—C group, it remains unchanged in the propionic esters, the first group 
of which consists of methyl, ethyl, and propyl propionate, the second beginning 
with the last-named ester. 
Lower Members Higher Members 
Group Number | Mean Difference} Number | Mean Difference 
of Values) calculated— of Values calculated — 
of A observed | of A observed 
° | ° 
Alkyl chlorides 2 + 2°70 5 —1:04 
» bromides 2 + 1:12 5 = 1°25 
3, iodides . 2 + 0°52 3 —1-0 
Tsoparafiins — _— 2 +0°57 
Toluene, &c. 1 +0°45 3 + 0°63 
o-Xylene, &e. . 1 +671 1 —0°5 
m-Xylene, &c.. 1 +4252 1 +407? 
p-Xylene, &c.. 3 Nya gill —0715 1 +0°65 
Diethyl benzene, &c.  . -f = — i — 0:05 
Olefines H,C = CHR ; Mile ss — | 3 —2°351 
$s RHC=CHR' . : — — hie te +0°5? 
Polymethylenes . 2 Lo — 2 —3'85 2 
Ethers A - : aoe. | +82 13 +112 
Aldehydes 2 +2°0 4 +13 
Hydrosulphides 2 + 3°55 1 -0°5 
Amines = ; 5 : 2 + 8:2 4 +17 
Esters. i : < tal hee ot +492 67 +1:53 
Associating Substances. 
ie) ° 
Cyanides . . 1 + 12°65 4 +2°9 
Nitro-methane, &c.. 2 +111 ] +3°85 
Ketones . 1 + 62 3 + 2.85 
Fatty acids 2 + 5:87 7 +1:58 
2 + 12°87 5 +65'24 
» alcohols 
