‘4,92 REPORT—1904. 
Of the seventeen series of non-associating substances there are only five for 
which the mean difference between the calculated and observed values of A for the 
higher members exceeds 1°°5. 
1. The m-xylene series. Here there is only one value, which, I think, is doubtful. 
2. The olefines, H,C=CHR. Here two of the three individual differences 
are less than 1°5; the temperatures are all below 0° and are somewhat uncertain. 
3. The polymethylenes. The difference for pentamethylene and hexamethy- 
lene differs by less than 1° from the calculated value. The B.P. of heptamethy- 
lene appears very doubtful. 
4, The amines. Ditferences somewhat erratic ; three within 1°:5 and two within 
0°5. Octylamine and nonylamine clearly incorrect and not included. 
5. The esters. Although Ramsay and Shields include these substances as 
non-associating, there is, I think, reason to suspect slight association. 
It will be seen that the differences are greater for associating than for non- 
associating substances ; also that they are greatest for the alcohols and least for the 
acids, although the factor of association is very high for both these series. In 
order to arrive at an explanation of these facts the effect of replacing hydrogen 
by chlorine may first be considered. 
The boiling-point of hydrogen chloride is not yet known accurately, but it 
must be about —80°. Thus, by replacing an atom of hydrogen in the hydrogen 
molecule by chlorine the boiling-point is raised from 20°-4 abs. to about 193° abs., 
or about 173°. On replacing an atom of hydrogen in methane by chlorine the 
rise of boiling-point is from 108°'8 to 249°3, or 141°. Ascending the series of 
paraffins the rise of boiling-point due to the replacement of hydrogen by chlorine 
diminishes rapidly at first, and then more slowly, being only 58°-5 in the case of 
octane. Thus the influence of the chlorine atom becomes relatively smaller as the 
formula weight of the alkyl group increases. 
Consider, now, the effect of replacing a hydrogen atom by a hydroxyl group. 
In the formation of water from hydrogen gas the boiling-point is raised no less 
than 352°°6, from 20°4 abs. to 373° abs., or in the ratio of 1 : 18°38; in the case of 
methane the rise is 221°8, from 108°'3 to 337°7, or in the ratio of 1: 3:12; with 
octane the rise is 65°-4, from 398°'6 to 464°; and with hexdecane itis only 56°°5, 
from 560°'5 to 617°, the ratio being 1 : 1:10. 
It will be seen that in the case of hydrogen the influence of the hydroxyl is 
enormously greater, and in the case of methane very much greater, than that of 
chlorine in raising the boiling-point, but that on ascending the series of paraflins 
to octane the influence of the hydroxyl group diminishes until it 1s little 
greater than that of the chlorine atom, and if is quite probable that with 
hexdecane it would be somewhat less. This is, no doubt, to be explained by the 
fact that the molecules of water and of the lower alcohols are highly associated 
in the liquid, but not in the gaseous state, and therefore, in order to vaporise the 
liquids, this molecular attraction must be overcome, and the temperature must 
therefore be raised. The molecular association diminishes, however, as the series 
of alcohols is ascended, and is probably slight in the case of octyl alcohol. If so, 
it would appear that the effect of the hydroxyl group—apart from association— 
in raising the boiling-point is not very different from, and is probably somewhat 
less than, that of the chlorine atom, and that the difference between the 
boiling-points of the lower alcohols and of the corresponding chlorides is entirely 
due to molecular association in the liquid state. 
With the acids there is association in the gaseous as well as the Jiquid state, 
and since, according to the tables given by Ramsay and Shields, the factor of 
association for a liquid fatty acid at its boiling-point is rarely greater, and in most 
cases is somewhat smaller, than for the corresponding liquid alcohol, the molecular 
attraction to be overcome on vaporisation must be considerably less for the acid 
than for the corresponding alcohol, and the resulting rise of boiling-point above 
the normal value must be less. An explanation of the very low values of A for 
the alcohols and the moderately low values for the acids is thus afforded. 
It would take up far too much time and space to give full details of the 
boiling-points of all the compounds considered, with the observed and calculated 
values of A; but it may, I think, be stated that tie difference between the boiling- 
