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XLIV. Some Experiments on Residual Ionization. 

 By K. H. Kingdon, M.A., University of Toronto*. 



[Plate X.] 



I. Residual Ionization in Acetylene. 



INTRODUCTION.— -If dry air be enclosed in a clean 

 zinc vessel and removed from the neighbourhood of all 

 ordinary ionizing agents, it is found, on measuring the con- 

 ductivity of the gas, that ions are being produced in it at the 

 rate of about 8*7 per c.c. per second. The production of these 

 ions is called natural ionization. If, however, the zinc vessel 

 be surrounded by a water-screen the natural ionization is found 

 to decrease ; and if the measurements be made over a con- 

 siderable body of water, such as the ocean or the great lakes 

 of America, the ionization in air is found to fall to a definite 

 minimum of about 44 ions per c.c. per second, which we 

 may call the residual ionization. The difference between 

 these two rates of ionization has been shown to be due to a 

 penetrating radiation from the earth's surface, which can be 

 cut off by a screen of water if sufficient thickness be used. 

 The possible components of the residual ionization appear 

 to be: — (1) a radioactive impurity in the gas, (2) a radio- 

 active impurity in the walls of the ionization-chamber, 

 (3) ionization by the collisions of thermal agitation. In an 

 effort to determine to which of these sources residual ioni- 

 zation should be attributed, McLennan and Treleavenf 

 measured the residual ionization in several gases, the results 

 obtained being as follows : — 



Gas. 



No. of ions per c.c. 

 per second. 



Carbon Dioxide 



4-83 

 1-11 

 632 



5-02 

 27-00 



Hydrogen 



Ethylene 



Nitrous Oxide 



Acetylene 





It will be noticed that in the above list the residual ioni- 

 zation in acetylene is very much higher than in any of the 



* Communicated by Professor J. C. McLennan, F.R.S. 



t J. C. McLennan and C. L. Treleaven, Phil. Mag. xxx. p. 415 (1915). 



