﻿Nuclei in Air and Vapours by Intense Cooling. 851 



can we get rid of the formation of nuclei, that is, of these 

 traces of vapour. 



We may, I think, therefore assume that in Mr. Owen's 

 experiments the nuclei consist neither of H 2 0, as the pre- 

 liminary drying was so extremely careful, nor of aggregates 

 of air molecules, but of aggregates f the before-mentioned 

 easily condensed gases and vapours, which are continuously 

 given off spontaneously from the walls and the phosphorus 

 pentoxide during the prolonged course of the experiment, 

 and also especially on the alteration of pressure during the 

 cooling, and which are formed through the action of cold 

 into nuclei. For however careful the drying and purification 

 may be, they do not suffice, according to our experience, to 

 remove these constituents, as it was impossible for Mr. Owen 

 to heat the taps, and the glass in their neighbourhood, 

 sufficiently; the evolution of gases from the phosphorus 

 pentoxide must also be taken into account. 



Apart from these considerations, our experiments give a 

 direct proof tlmt, if the air were completely freed from the 

 minor constituents mentioned, the phenomena could not 

 have occurred *. We boiled off air from liquid air, and 

 brought the current of air at once to the room temperature 

 by passing it through a thin glass tube immersed in cold 

 water ; the vessel where the gas was subjected to the rays 

 and all the tubes leading to it had been previously heated to 

 500° 0. The air was then subjected to Schumann ultra-violet 

 light (wave-length less than 180 /a/jl), which, according to 

 our experiments, produces carriers of electricity in the chief 

 gases of the atmosphere, owing to its selective absorption. 

 With this arrangement the aggregates of; air molecules 

 observed by Mr. Owen ought cert duly to have been present, 

 as the air immediately after vaporising possesses a temperature 

 more than sufficiently low; the aggregates ought also to have 

 persisted during their passage to the vessel where the air is 

 exposed to the rays, as the duration of this passage was much 

 shorter than in Mr. Owen's experiments. The aggregates 

 would have been detected in the measurements by the com- 

 bination with carriers of electricity which always takes place. 

 However, only carriers of about molecular size were observed, 

 which are formed from the gas itself, and, for instance, do 

 not have any effect on Helm hoi tz's steam-jet. 



It is thus made certain that these molecular aggregates 

 are not formed in very pure air, and thus that they must be 

 conned of the minor constituents, which are always present 



* Lehard and Ramsauer, hc.cit. See Part V. 

 3 K 2 



