﻿produced by Action of Light on Iodine Vapour. 419 



small an amount of water as 8 grams or less is used to clean 

 the glass-wool, nuclei are produced which exceed very much 

 in number the maximum effect obtained when using the 

 glass walls of the apparatus (although it had, previous to the 

 cleansing, produced practically no nuclei, no matter how 

 much air was drawn through it), and this action continued 

 for more than a fortnight. Hence in this case, if we adopt 

 Ramsauer's theory, 8 grams of water would hold enough 

 impurity to keep the effect in action at a somewhat 

 accelerated rate for fourteen days. It is easy to see that we 

 adopt a very low estimate when we say that 8 grams of 

 water in the one case produces at least seven times the effect 

 of 200 grams in the other. 



When the glass-wool is freshly used and presumably 

 saturated with impurities, the effect has practically disap- 

 peared in two days. To explain the continuance of the effect 

 for a fortnight on a subsequent occasion, other circumstances 

 being the same, we should have to assume that either all the 

 impurity was not exhausted in the first case, or else we get 

 a considerable supersaturation in the second. Both these 

 explanations seem untenable. The experiments with the 

 glass-wool show that the effect obtained does not depend 

 upon the amount of water used, but on the amount and 

 nature of glass surface exposed. This is particularly brought 

 out in the experiments with the specially purified water. 

 All the experiments support the third explanation that the 

 nuclei are produced in a chemical action between iodine and 

 oxygen and probably water-vapour aided by a catalytic 

 property of glass. The increased action produced by the 

 glass-wool is explained by its greater catalytic property. 

 The disappearance of the effect is explained by the disap- 

 pearance of the catalytic property, caused probably by the 

 deposition of iodine or one of its products upon the glass 

 surface. If this explanation is correct, then the action of 

 the glass walls of the apparatus must be catalytic also. 



The second explanation, that the action ceased because 

 chemical equilibrium w T as established, is not essential and 

 there are many objections to this theory. All the experi- 

 mental facts are consonant with the third explanation, but I 

 am unable definitely to state that it is the correct one. 



In conclusion I desire to express my thanks to Professor 

 Beattie for his very kind interest in the experiments and for 

 placing the resources of the South African College Laboratory 

 at my disposal. 



2E2 



