gases was published by Matteueci* in 1850. He found the loss to be the same in air, carbonic acid, and hydrogen. Warburg,t in 1872, found the loss in air and carbonic acid to be equal, and in hydrogen about half as great. They used much larger vessels, and it is probable that in Warburg's experiments the saturation current was not approached, so that the leakage was not even approximately pro- portional to the ionisation ; it is perhaps in this way that the discre-
Relative Conductivity (Air =1).
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Gas.
Kadium rays
(penetrating
type).
Polonium
rays.
Spontaneous
lonisation.
Air
1-00
1 00
1 "00
-157
0-226
'184
Carbonic acid
1 -57
1 -54
1 '69
Sulphur dioxide
2-32
2 '04
2 '64
4-89
4-44
4'7
paricy is to be explained. In Matteucci's experiments, however, the leakage was independent of the potential ; he was therefore using potentials high enough to produce the saturation current, and some other explanation is in this case required. One possible way out of the difficulty would be to suppose that the ionisation ig to be explained by a slight radio-activity of the walls, the radiation being of only moderate penetrating power. In a large vessel all the radiation might be absorbed even by hydrogen, and in that case we should expect to find the same total number of ions produced in a given time whatever gas the vessel contained.! At the same time the similarity between the results obtained for the relative ionisations of different gases in the small vessel with those of the same gases exposed to the action of radium would be explained (the ionisation being due to a similar cause), as also would the departure at the higher pressures from the simple law connecting pressure and rate of leak, which holds for the lower pressures, for at the higher pressures the intensity of the rays might be considerably reduced by absorption before reaching the central portions of the vessel.
Until, however, further experiments have been made it would, I think, be premature to conclude that the ionisation is due to radiation from the walls of the vessel.
- ' Annales de Chimie et de Physique,' vol. 28, pp. 385-429.
t ' Annalen d. Physik u. Chemie,' vol. 145, pp. 578-599.
J As in gases exposed to uranium rajs in a large veisel (Rutherford, ' Phil. Mag.,' vol. 47, p. 136, 1899).
