NUCLEAR CONDENSATION OF CERTAIN ORGANIC VAPOURS. 
463 
I have calculated a for the following substances :— 
Radius of Drop with Charge 3 - 25x 10~ 10 Electrostatic Units in Equilibrium with 
the Saturated Vapour at 17° C. 
a. 
a. 
Water. 
cm. 
3-02x10“ 8 
Butyric acid. 
cm. 
4-3x 10“ 8 
Ethyl acetate. 
4-4 
Iso-butyric acid .... 
4-5 
Methyl butyrate .... 
4'4 
Methyl alcohol .... 
4-5 
Methyl iso-butyrate . . . 
4-4 
Ethyl alcohol. 
4-5 
Propyl acetate. 
4-4 
Propyl alcohol. 
4-5 
Ethyl propionate .... 
4-4 
Iso-butyl alcohol .... 
4-5 
Formic acid. 
3-8 
Iso-amyl alcohol .... 
4-5 
Acetic acid. 
4-5 
Chloroform. 
4-3 
Propionic acid. 
4-3 
(Radius of N 2 molecule 1 - 41 x 10 8 cm., 0 2 1 - 35 x 10~ 8 cm.)* 
The surface tensions used in calculating the above tables are from Ramsay and 
Shields’! and Ramsay and Astons! determinations, which were made with only the 
liquid and vapour present in the measuring apparatus. 
This value of a is practically the same for the organic liquids, with exception of 
formic acid. The volume of one of these organic liquid drops would be three times 
that of the water drop in equilibrium with aqueously saturated air at the room 
temperature. 
Calculated Supersaturation. 
According to the theory we are considering, the presence of electrically charged 
nuclei in a vapour will cause it to condense and form small drops. The charge on 
these drops tends to make them grow larger, while their surface tension tends to 
make them evaporate. Their size, when in equilibrium with the vapour, depends on 
its pressure. There will be a pressure which will enable the drops to grow to such a 
size that the effect of surface tension will be overcome, and, if the vapour pressure be 
kept up, the drop will become very large. In a condensation experiment in which 
the expansion is just sufficient to cause condensation, the vapour pressure at the 
instant when the expansion ends is sufficient to make the very small (invisible) drops 
grow to a large size. Professor J. J. Thomson§ has shown how this last vapour 
pressure may be found. 
* Jeans, ‘Dynamical Theory of Gases,’ Cambridge, 1904, p. 340. 
t ‘ Phil. Trans.,’ A, 184, p. 647 (1893). 
\ ‘ Roy. Soc. Proc.,’ 56, p. 163 (1894). 
§ ‘Conduction of Electricity through Gases,’ 2 nd Edition, p. 180 (1906). 
