Prof. Thomson , On the increase in electrical conductivity , etc. 505 
On the increase in the electrical conductivity of air 'produced 
hy its passage through water. By Professor J. J. Thomson. 
[Read 5 May 1902.] 
In continuation of the experiments 1 brought before the Society 
last term the author investigated the effect produced on the con- 
ductivity of air by bubbling it through water. The air from a 
large gas-holder of about 350 litres capacity was bubbled vigor- 
ously through water by making the air in the vessel circulate 
through a water pump : this treatment increased the conductivity 
of the air, and when the bubbling had been going on for some 
time the conductivity of the air was 10 or 12 times the initial 
conductivity. 
When once the air has been put in this highly conducting 
state it stays in it for a very considerable time; a large part of 
the conductivity produced by the bubbling remains in the air 
48 hours after the bubbling has ceased; nor does it disappear 
when an intense electric force is kept applied to the gas. The 
effect produced by the passage of the air through water is similar 
to that which would be produced if the bubbling produced a 
radio-active ‘ emanation ’ similar in properties to those emitted by 
thorium and radium. The conducting gas can be passed from 
one vessel to another ; it retains its conductivity after passing 
through a porous plug : passage through a long tube heated to 
redness destroys the conductivity; it takes however a very high 
temperature to do this, temperatures less than 300° or 400° C. 
seem to produce comparatively little effect ; if the gas is passed 
very slowly through a long tube filled with beads moistened with 
sulphuric acid the conductivity is destroyed ; unless however the 
stream of gas is very slow, the air retains a good part of its con- 
ductivity in spite of the sulphuric acid. Another point of resem- 
blance between the ‘ emanation ’ from radio-active substances and 
a gas in this state, is that if a strongly negatively electrified 
conductor be kept in the gas for some time the conductor becomes 
radio-active : this activity was only reduced by about 20 °/ 0 when 
the conductor was washed in water and then heated in the flame 
of a Bunsen burner ; the radio-activity reduced in this way disap- 
pears in the course of a few hours. 
1 On Induced Radio-activity, page 504. 
