McClelland and Nolan — Ions Produced through Mercury. 33 



mobilities of these different groups of ions and for the constancy of the ratios 

 of their mobilities during the process of growth. 



1. We might assume that all the- ions are the same size at any instant, 

 and will, therefore, take on water-vapour at the same rate, and in this way 

 we can get an explanation of the constancy of the ratios. We would then, 

 however, have to explain the different mobilities by different charges, and 

 it is difficult to see how different charges could possibly give us the steps in 

 mobility we have observed. It is extremely improbable that the correct 

 explanation can be found on any assumption of variable charges on similar 

 nuclei. 



2. We might assume that the ions consist of water-globules of different 

 sizes having the same charge, or we need make no assumption regarding the 

 charge if the mobility of such ions is approximately independent of the 

 charge. The fact that both the mobility and the rate of taking on water would 

 depend on the size of the globule might result in the ratios of the mobilities 

 being approximately constant. The five separate ions in their final steady 

 state would from this point of view be five globules of different sizes, each 

 possessing some degree of stability. 



The objection to this view is that we have ions proceeding past certain 

 apparently stable sizes until each arrives at its characteristic size. The 

 difjficulties in the way of this hypothesis are very great. 



3. We can modify this assumption (2) in a way that removes the serious 

 difficulties in accepting it. Let us assume that there is one stable size of 

 water-globule, and that the five different ions consist of groupings of different 

 numbers of these globules. Before the steady state is reached each globule is 

 taking on water, and, therefore, the grouping which constitutes an ion is 

 growing at a rate depending on the number of globules it contains. The 

 constancy of the ratios of the mobilities is at once explained on this theory. 



As an example of how such groups may be built up, we may start with a 

 single globule carrying a unit charge and having a certain mobility. The next 

 ion may contain a number of these globules, say three, two positive and one 

 negative, or two negative and one positive. Such an ion might have approxi- 

 mately one-third the mobility of the single globule. Similarly some grouping 

 of these ions might form a still more complex and more slowly moving ion, 

 and so on. It may be noticed that the average of the observed mobility 

 ratios is about 3"4. 



It is possible that on some such lines as are here indicated an explanation 

 of the different groups of ions may be found. According to this view ions of 

 each class combine to form the next slower class, and if sufficient time is 

 given we should have an excess of the slowest and most complex ion. Certainly 



E.I. A. PROC, VOL. XXXni., SECT. A. [5] 



