NUCLEAR CONDENSATION OF CERTAIN ORGANIC VAPOURS. 
467 
The results of these experiments, as a whole, were more regular than those obtained 
when the air and vapour were ionised by Ildntgen rays. The number of expansions 
made in order to determine v 2 /v 1 varied from 7 to 20 for the different substances, and 
on the average was 14. 
After acetic acid had been exposed to the rays from radium or from thorium very 
inconsistent observations were obtained- _ _ _ _ 
The vapour pressure n 1 of tertiary amyl alcohol was assumed to be between 5 and 
15 mm. at 17° C. # in order to calculate the expansion. 
Air and Water. Natural Nuclei. 
No drops : 1'242, l - 242, l - 250, 1 252, 1"254. 
Drops: D256, D258, 1-260, D262, D262, D266. 
Least expansion for condensation 1/256. 
C. T. It. Wilson,!' using a small apparatus, found l - 252. Immediately before the 
above experiments the following observations were obtained with the apparatus, the 
air and water vapour being exposed to Lontgen rays during the expansion. 
Air and Water. Rontgen Rays. 
No drops : 1/208, D218, 1'220, 1-224, 1‘226, 1’230, D230, D234. 
Drops: 1"236, 1’240, D240, 1"241, 1;252 (thin cloud). 
Thus least expansion for condensation is 1’236; 1/247 (Wilson). | The least 
expansions for condensation found from experiments just described are given in the 
second column of the table on the following page. 
The nuclei in the condensation we are considering must be the natural ones present 
in the dust-free air. Wilson found, as we saw earlier in this paper, the same 
expansion caught the natural nuclei as caught the nuclei produced by Rontgem 
Becquerel, and other rays ; and he showed also that the natural nuclei could be 
removed by an electric field, so they were the ions which normally exist in the air. 
* The vapour pressure of tertiary amyl alcohol at 17° C. has not been determined. It may be calculated 
thus : If x.®n represents the absolute temperature when a liquid A has a vapour pressure v, then we know 
that 
wateiAtio/tertiary amyl alcohol^760 = 373/374'8 = O'9975. 
Now this ratio is known to vary only slightly with the temperature; for several alcohols it changes 
+ 0'0002 per degree. Therefore the temperature of water when it has the same vapour pressure as tertiary 
amyl alcohol at 17° is 
watcrff = tertiary amyl ak-oholff * 0 98 = 290 X 0 98 = 284 . 
But at 273 J + 11“ n for water is 9'8 mm. So, according to this reasoning, v for tertiary amyl alcohol at 
273 + 17 is 9-8 mm. 
t ‘Phil. Trans.,’ A, 189, p. 265 (1897). 
{ 1 Phil. Trans.,’ A, 192, p. 408 (1899). 
