On the conductivity of salt vapours

Abstract

It has been shown by Bettie, Garrett, and Garrett and Willows, that when certain salts are heated up to 300-400ºC. one can observe the discharge of positive and negative electricity. This phenomenon is observed more particularly in the case of the halogen salts of cadimum, zinc and ammonium. The researches of Schmidt and Sheard have shown that the discharge is due to two factors, (1) emission of the charges from the surface of the heated salt, and (2) to the conductivity of the salt vapours themselves. The thermionic effect of the above-mentioned salts was studied in detail by Prof. O. W. Richardson and his pupils, while some investigations of the electrical properties of the salt vapours were made by Schmidt in the papers referred to above. The object of the present research was to the current passing in the salt vapours. The Thermionic Effect of the Salt and the Conductivity of the Salt Vapours. Some experiments were carried out in order to test whether the conductivity of vapours is due to charges which have diffused to other parts of the apparatus from the surface of the heated salt. For this purpose the vapours were investigated after passing through a cylindrical condenser in which the electric force was strong enough to sweep all charged particles to the electrodes. The apparatus used consisted of a small bulb A (fig. 1), in which the cadmium iodide was placed. The vapour at first passed through the plug of glass wool B to stop the large ions which might be produced during the heating of salt, then entered the condenser K 1 , where the smaller ions could be removed by the electric field. The outer coating of the condenser K 1 was obtained by platinising the inner surface of gases tube with a "liquid platinum" (from Deutsche Gold und Silber Scheide Anstalt) and was connected to earth. As the inner coating of the condenser a glass rod covered with the same substance was used, and was connected by a a platinum wire the source of electromotive force.