NUCLEAR CONDENSATION OF CERTAIN ORGANIC VAPOURS. 
459 
Discussion of Results. 
The values of the expansion in the last table are thought by the writer to be 
accurate to O'Ol. An error in a value of the expansion gives rise to a larger error in 
the value of the supersaturation derived from it. This will be seen on examining the 
figures for iso-amyl alcohol, for which an expansion of R218 means a supersaturation 
of 5‘49, and an expansion of 1T82 an S of 4’02. In this case an error of O’Ol 
(0*8 per cent.) in the expansion gives rise to an error of 0'4 (8 per cent.) in the 
supersaturation ; similar figures hold for the other vapours. Besides the error arising 
from an error in the expansion, another is introduced in the supersaturation in 
calculating it by the formula 
Q TTl U 62 
& = — • — • ~a > 
7^2 ^2 t'l 
for tt 2 , the saturated pressure of the vapour at the low temperature at the end of the 
expansion, has to be found in several cases by extrapolation. Though all the vapour- 
pressure data available have been used, and the inter- and extrapolations have been 
made with the greatest care by Ramsay and Young’s method, by the Kirchhoff- 
Rankine formula 
logy) = A + B/d + C log 6, 
and by graphical methods, it has not been possible to obtain very accurate values of 
7 r 2 * in the case of the acids. We cannot expect, then, that the relation between the 
chemical constitution of a vapour and the supersaturation causing condensation in it 
to be very precise. Some general relationships, however, seem clear. 
Super saturation and Chemical Constitution. 
In the case of the esters and acids the supersaturation decreases with increasing 
molecular weight. Ethyl propionate, and the isomers butyric and iso-butyric acids, 
are exceptions to this statement. Of the four isomeric esters, three, namely, methyl 
butyrate, methyl iso-butyrate, and propyl acetate, have (to quite as high a degree of 
accuracy as could be expected) the same supersaturation, namely, about 5 2. Ethyl 
propionate deviates from this value. The isomers n-butyric acid and iso-butyric acid 
have also approximately the same supersaturation. 
In the case of the alcohols, after the first of the series the supersaturation increases 
regularly with the molecular weight, thus :— 
* Where 7 t 2 had to be calculated, the extrapolation was made by two of the above-mentioned methods, 
and in every case these two results were found to agree as closely as the observations of different 
observers when extrapolated agreed among themselves. 
3 n 2 
