Prof. Thomson, On the increase in electrical conductivity, etc. 505 



On the increase in the electrical conductivity of air 'produced 

 by 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 °/„ 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. 



