NUCLEAR CONDENSATION OF CERTAIN ORGANIC VAPOURS. 
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Summary. 
(1) The least expansion which causes condensation in air initially saturated with 
an organic vapour and ionised by Rontgen rays has been determined for five esters, 
six acids (formic to iso-valeric), and iso-amyl alcohol. 
(2) In the case of acetic acid the expansion required was greater for feeble X-rays 
than for more intense ones. 
(3) The supersaturation S existing at the end of each of the expansions mentioned 
in (1) has been calculated, and also for four alcohols and chloroform, from Przibram’s 
experiments. 
(4) The acids are found, on the whole, to have the largest values of S and the 
alcohols the least. The isomers examined have the same value for S, with one 
exception. In the case of the alcohols, ethyl to iso-amyl, a fairly regular decrease in 
S accompanies the addition of a CH 2 group. 
(5) The existing theory of condensation on ionic nuclei has been given, values of S 
have been calculated from it, and compared with S deduced from the observed 
expansions. The agreement in the case of acetic, propionic, n-butyric, and iso-butyric 
acids and methyl alcohol is very close. 
(6) The expansion and supersaturation necessary for condensation on the natural 
nuclei have been determined for the same (dust-free) vapours. In the case of formic, 
acetic, and butyric acids a distinctly greater expansion is required to catch the 
natural nuclei than that required for the ionic nuclei produced by Rontgen rays. 
(7) As the expansion was increased in the absence of artificial ionisation the 
number of drops usually increased continuously with it, so that the fog-point was ill 
defined, except in the case of tertiary amyl alcohol. 
(8) Ethyl acetate, methyl butyrate, propyl acetate, acetic acid, iso-amyl alcohol 
were found to condense for a smaller supersaturation on the positive nucleus than on 
the negative. Water is the only known substance for which the negative ionic 
nucleus is more efficient than the positive. 
(9) On bubbling air through methyl, ethyl, and iso-amyl alcohols, ethyl acetate, 
propyl acetate, methyl butyrate, chloroform, and ethyl iodide they became negatively 
electrified. This was the sign of the electrification to be expected from Professor 
1 homson’s double-layer theory of the relative efficiency of ionic nuclei. 
I wish to thank Mr. C. T. It. Wilson for most helpful discussion, and Professor 
Thomson for many suggestions and his inspiring interest. 
9 OCX 190R 
