268 Mr Kleeman, The Unstable Nature of the Ion in a Gas. — 
| 
Some experiments by Latty, Frank, and Townsend on the — 
velocity and diffusion of ions have a bearing on the clustering | 
effect under consideration. Thus Latty* found that the velocity 
of the negative ion in air specially dried is much greater than that | 
usually observed. Moreover, the velocity did not vary inversely as | 
the pressure of the air under these circumstances, For example, | 
a velocity of 173 cm. per second was obtained for the negative ion | 
in air at a pressure of 10 mm. of mercury on applying an electric — 
force of °5 volt per cm., which is about 100 times the velocity | 
obtained under ordinary conditions, On increasing the electric | 
field to ‘9 volt per cm. the velocity rose to 1845 cm. per second. 
It appears therefore that a cluster in air composed of an elementary | 
ion and water and possibly air molecules, is much more stable — 
than when the cluster is composed of air molecules only. 
Frankt found that the velocity of a negative ion in carefully 
purified argon is 206°3 cm. per second, but that it falls to 17 em. 
per second on adding about one per cent. of oxygen. A cluster in 
argon composed of argon molecules only is thus very unstable and 
has a correspondingly short period of life, but its stability is 
greatly increased when oxygen molecules enter into its com- — 
position. | 
Townsend} found that when a gas has been subjected to a 
drying process for several days the rate of diffusion of the negative 
ions greatly increases, and does not obey the ordinary laws of 
diffusion. The effect seems to be greater with H, than with O,, 
and much greater with these gases than with CO,. A cluster in 
CO, composed of an elementary negative ion and CO, molecules 
thus seems to be comparatively stable. 
When the ions are drawn through the gauze (see fig. 1) in 
experiments of the nature described in a previous part of the 
paper, a certain fraction (which may have any value lying between 
unity and z ) should be, as we have seen, in the elementary state, 
and thus be in a state fit for the production of ionisation by 
collision if the electric field be sufficiently large. Further ions 
become elementary on their passage from the gauze to the plate, 
and the number of initial ions available for the production of 
ionisation by collision is thus increased. It will be of importance 
therefore to obtain a formula for the current observed under these 
conditions when the field is sufficiently large to produce fresh ions 
by collision of ions. The case when fresh ions are produced by 
collision of the negative ions only will be considered first. 
Let K denote the total number of ions drawn es the 
* Proc. Roy. Soc. A, vol. uxxxiv. 1910. 
+ Verh. d. Deut. Phys. Gesell. March, 1910, pp. 291298. 
+ Proc. Roy. Soc. A, vol. LXxxy. pp. 2529, 1911. 
