Artificial Condensation Nuclei and Relative Humidity


WORKING at Heidelberg, during 1942–44, I have investigated the change in size of artificially produced condensation nuclei with variation of relative humidity, by measuring the diminution of conductivity of air through ion-adsorbing suspensoids in a chamber ionized by gamma rays. A differential compensation method was used, the principle of which was first indicated by Greinacher in Switzerland in 1922. The results enabled a new examination to be made of the theory of the growth of solution nuclei with relative humidity, commonly associated with the name of the Norwegian scientific worker Koehler. I have been able to show that, contrary to the accepted view, substances of different hygroscopic power, namely, strongly hygroscopic, less hygroscopic and non-hygroscopic particles, show very different behaviour. Compared with the extreme importance of the individual chemosorptional hygroscopicity, other characteristics do not seem to influence considerably the growth of the nuclei with relative humidity. Salt nuclei generally showed no tendency to crystallize even at low humidities.

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DALAL, N. Artificial Condensation Nuclei and Relative Humidity. Nature 157, 549 (1946) doi:10.1038/157549a0

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