| Mr Kleeman, The Unstable Nature of the Ion in a Gas. 267 
to one another in the case of the former gases. It follows there- 
fore that the ratio of the abscissae of two points one on each of 
the steep part of two curves of the type A and B corresponding 
to a common ordinate, should be approximately independent of 
‘the pressure of the gas. This was found to be the case. We may 
therefore as a first approximation take this ratio as a relative 
‘measure of the proportion of free ions to clusters in a gas. It was 
found that in the majority of the gases mentioned this ratio was 
approximately the same as that obtained with ether. The gases 
‘which showed a considerable deviation from this were carbon 
tetrachloride, carbon disulphide, benzene, air, oxygen, chloroform, 
and hydrogen, whose ratios were considerably greater than the 
ratio obtained with ether. Especially was this the case with 
earbon tetrachloride, carbon disulphide, and benzene; for these 
three gases the curves obtained almost coincided with one another. 
It follows therefore that the proportion of free ions to clusters in 
these particular gases is considerably greater than in the case of 
the other gases in which the relative ionisation for y rays is the 
same as for a rays. 
The separation of the curves obtained with the gases con- 
taining bromine and iodine atoms in their molecules was about 
the same as that obtained with ether. This separation is in part 
due to the greater relative ionisation of these gases with y rays 
than with a rays. But the difference in ionisation accounted only 
for a small part of the separation. We may therefore conclude 
that these gases fall into line with the majority of the other gases. 
It will be of interest here to consider theoretically the be- 
haviour of ion clusters in gaseous mixtures. In one of the papers 
quoted it is shown that c, =t,n,, where c, denotes the concentra- 
tion of the ion clusters of the type n, t, the period of life of a 
cluster, »,, the number of clusters changing into other clusters 
per second. Now the quantities ¢, and n, depend directly on 
the nature of the collision between a cluster and the surrounding 
molecules. Thus when a cluster collides with a molecule the 
latter will have a dissolving or dissociating action upon the cluster 
due to electrostatic induction, chemical attraction, etc., apart from 
the kinematical effect of the collision. Therefore when two gases 
are mixed the ratio of free ions to clusters is not likely to be the 
mean of the ratios of the constituent gases, but may be much 
greater or much smaller, even if no new kinds of clusters are 
formed after mixture of the gases. Thus the behaviour of a 
mixture of gases can hardly be predicted from that of its con- 
stituents. 1f new kinds of clusters are formed after mixture of the 
gases, matters are still further complicated, and we may be quite 
sure then that the ratio is different from the mean of the ratios of 
the constituent gases. 
