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X. On the Electricdl Conchictirify of A ir and Salt Vapours. 
By Harold A. Wilson, D.Sc., M.Sc., B.A., Allen Scholar, Cavendish Lahoraloi-y, 
Cambridge. 
Communicated by Professor J. J. Thomson, F.R.S. 
Received Mai’ch 11,—Read March 28, 1901. 
The experiments described in this paper were undertaken with the oliject of olitaining 
information on the variation of the conductivity of air and of salt vapours with 
change of temperature, and on the maximum current which a definite amount of salt 
in the form of vapour can carry. Tliey are a continuation of the two researches'^”' on 
the same subject jiuhlished in 1899 . 
In the paper “ On the Electrical Conductivity and Luminosity of Flames ” some 
observations on the variation of the conductivity with the temperature at difterent 
heights in the flame are given. They indicate a rapid increase in the conductivity 
with rise of temperature. 
Tlie method employed in the experiments now to he described was the foliowiiig :— 
A current of air containing a small amount of a salt solution in suspension in the 
form of spray was passed through a platinum tube heated in a gas furnace; this tube 
served as one electrode, and the other was fixed along its axis. The temperature of 
the tube was measured by means of a platinum platinum-rhodium thermo-couple, and 
the amount of salt passing through the tube was estimated by collecting the spray in 
a glass-wool plug. From the temperature variation of the conductivity the energy 
retpiired to produce the ionization can be calculated, and this compared witli the 
energy required to ionize bodies in solutions. 
Since the publication of the researches just referred to several papersf on the 
conductivity of salt vapours in flames Ijy Hr. E. Marx liave appeared. The first of 
these is concerned mainly with the fall of jiotential between the electrodes, and the 
* Harold A. Wilson, “ On the Electrical Conductivity of Flames containing Salt Vapours,” ‘ Phil. 
Trans.,’ A, vol. 192, 1899. A. Smithells, H. M. DxIWSON, and H. A. Wilson, “The Electrical 
Conductivity and Luminosity of Flames containing Vaporised Salts,” ‘ Phil. Trans.,’ A, vol. 193, 1899. 
t Von Erich MxVRX, “ Ueber den Potentialfall und die Dissociation in Elammengasen,” Gesellschaft 
der Wissenschaften zu Gottingen,’ 1900, Heft 1; ' Annalen der Physik,’ 1900, No. 8. “Ueber das 
Hall’sche Phanomen in Flammengasen,’ ‘ Annalen der Physik,’ 1900, No. 8. 
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22.11.1901. 
