On Flames containing Vaporised Salts. 145 



measurement of the amount of salt was attempted by a photometric 

 method. It appeared that the amount of salt conveyed to the flame 

 was about eighteen times as much as in the corresponding experiments 

 of Arrhenius, so that it was possible to investigate the conductivity of 

 salt vapours at greater concentrations than was done by Arrhenius. 



7. Relation between Current Strength and Electromotive Force. 



Experiments were made with a large number of salts, and with a 

 difference of potential between the electrodes varying from O'Ol volt 

 to 45 volts. The results show that with small E.M.F.'s up to O2 volt, 

 Ohm's law is accurately obeyed. With greater E.M.F.'s the law is not 

 obeyed, the deviation becoming greater in increasing proportion as the 

 E.M.F. is increased. 



The general relationship between current strength and E.M.F. was 

 expressed by Arrhenius as follows : 



C = A/(E), 



where C is current strength, E the E.M.F., and A a constant dependent 

 on the solution sprayed. This expression is only valid for the pre- 

 sent results within certain limits. With the more concentrated solutions 

 it is not applicable. 



Acting upon a suggestion of Professor J. J. Thomson, the authors 

 have found an equation capable of expressing the relationship between 

 C and E in a remarkably complete way. This equation is based upon 

 the work of Thomson and Eutherford* on the passage of electricity 

 through gases exposed to E-ontgen rays, a phenomenon which has 

 several points of external resemblance to that of conduction through 

 flames. The equation is 



where i bears the same relation to the E.M.F. as the current in X ray 

 conductivity. Tables are given in the paper showing to what extent 

 the above equation expresses the results obtained. 



8. Influence of Temperature on Conductivity. 



Experiments were made in which the electrodes M r ere raised or 

 lowered, so as to bring them into regions of different temperature. 

 The temperature differences were measured by means of a platinum 

 platinum-rhodium thermocouple. The results showed that the con- 

 ducting power of the salt vapour increased very rapidly with increasing 

 temperature, and that at temperatures not greatly below those which 

 the vapour attains in flames, the conductivity would become inappre- 

 ciable. 



* ' Phil. Mag.,' rol. 42, p. 392, 1896. 



