﻿produced by Action of Light on Iodine Vapour. 417 



iodine and the Wilson's apparatus was renewed by rinsing 

 the apparatus with distilled water, and the properties of the 

 nuclei produced were the same, except possibly in size, as 

 those produced by the glass-wool. Since the effect produced 

 in the glass-wool is renewed by drawing distilled water over 

 its surface, the conclusion seems irresistible that the nuclei 

 produced in the two cases are due to the same chemical 

 action. 



The question arises, what is the nature of this chemical 

 action ? In the communication referred to above we gave a 

 discussion of this. Three possible kinds of chemical action 

 were considered : — 



1. That the chemical action was one between the iodine 

 and some impurity on the surface of the glass. 



2. That the chemical action was a surface action between 

 the glass and the iodine or one of its chemical compounds. 



3. That it was a chemical action between iodine and 

 water-vapour and oxygen caused by a catalytic action of 

 the glass. 



We considered that the weight of evidence entitled us to 

 reject the impurity explanation in the case of the Wilson's 

 apparatus alone, and this conclusion I now extend to the 

 glass-wool. We considered that the second explanation was 

 the correct one for the Wilson apparatus, and that the third 

 explanation might explain the results when using glass-wool. 



Ramsauer objects to this view and puts forward the 

 following evidence in favour of the first explanation *. 



He says : — " In explanation of the effects there described 

 I should like to call attention to our experiments t, where we 

 have shown that glass-wool and every glass surface that has 

 not been strongly heated continuously gives off adsorbed 

 minor constituents of the air, which on the production of ozone 

 by ultra-violet light always lead to the formation of nuclei ; 

 now, according to Mr. Owen himself, ozone is formed in his 

 experiments. The regeneration of the effect on washing the 

 walls with distilled water is explained by the fact that the 

 water must contain dissolved small quantities of the vapours 

 and gases mentioned before % (for instance NH 3 ), and as it 

 trickles down gives these up to the glass walls through 

 adsorption. These observations led us to construct asbestos 



* Phil. Mag. May 1912. 



t P. Lenard and 0. Ramsauer, " Ueber die Wirkungen sekr kurzwel- 

 ligen ultravioletten Lichtes auf Gase imd iiber erne Sehr reiclie Quelle 

 dieses Lichtes," Heidelberqer Akademie. Five parts : I. Aug. 2, 1910 : II. 

 Nov. 5, 1910; III. Dec. 20, 1910; IV. June 9, 1911 ; V. Aug-. 4, 1911. 



\ 0O 2 , NIL,, organic vapours, etc. 



Phil. Mag. S. 6. Vol. 29. No. 171. March 1915. 2 E 



