112 VAPOR NUCLEI AND IONS. 



conceivable that the action of coal gas on vulcanized rubber may in a 

 somewhat similar way to carbon disulphide be productive of nuclei. 



If these are larger than colloidal nuclei, though they may still be 

 much smaller than ions, they would pass through the filter and give rise 

 to the very phenomenon of depression of asymptote observed in table 43. 



75. Conclusion. Neither from the cases of C0 2 nor of coal gas does it 

 follow that coercible gases have larger colloidal nuclei than non-coercible 

 gases like air. The apparent results are the reverse of this. If the 

 increased difficulties of condensation in the former are due to smaller 

 heat ratios (y) as compared with air, there is no reason why C0 2 , where y 

 is larger, should show greater condensation difficulties than coal gas 

 where y is smaller. The distributions of nuclei suggest a common law 

 of dissociation or chemical equilibrium. 



COLLOIDAL NUCLEI AND IONS IN DUST-FREE AIR SATURATED 



WITH ALCOHOL VAPOR. 



76. Introductory. In my report* on the solutional nucleus and else- 

 wheref I came to the conclusion that the differences in promoting con- 

 densation exhibited by positive and negative ions were more probably 

 to be ascribed to the difference in chemical structure or composition 

 involving a difference of size than to the electrical differences as such. 

 Experiments made in Wilson's apparatus by Dr. DonnanJ with vapors 

 of methyl and ethyl alcohol, carbon tetrachloride, carbon disulphide, 

 benzol, and chlorobenzol show that the supersaturation needed to produce 

 condensation was not necessarily greater in ionizing than in non-ionizing 

 solvents. With similar apparatus Dr. K. Przibram recently examined 

 a series of alcohols and other bodies ionized by the X-rays, obtaining 

 among a variety of data a noteworthy result with a direct bearing on the 

 question here at issue. It appears that whereas in the case of water 

 vapor the negative ions are more efficient condensation nuclei than the 

 positive ions, the reverse holds for the alcoholic vapors. In cases of 

 methyl, ethyl, amyl, and heptyl alcohols (including some other bodies 

 like chloroform) the positive ions invariably require less supersaturation 

 to precipitate condensation than the negative ions of the same body. 



Interesting differences are therefore manifest in the behavior of 

 vapors, and it seemed desirable to test the nucleation of a medium of 



* Structure of the Nucleus. Smithsonian Contrib., No. 1373, p. 161, 1903. 



t Ions and Nuclei, Nature, lxix, p. 103, 1903. 



JF. G. Donnan: Phil. Mag. (6), ill, pp. 305-310, 1902. 



J K. Przibram: Wien Ritzungsber., cxv, pt. no, pp. 1-6, 1906. 



