TRANSACTIONS OF SECTION A 



547 



pumped off and measured in a constant volume burette at a known temperature 

 near that of the atmosphere, the relative volumes of bulb and burette being such 

 that the pressure on the gas in the constant volume burette -was as nearly as 

 possible that under which the gas was confined in the constant pressure bulb at 

 the lower temperature. By the above arrangement errors due to uncertainty in 

 the temperature of connections, &c., are eliminated. 

 The results are as follows : — 



These results indicate that the volume coefficient varies with the pressure on 

 the gas at the lower temperature, and if these values are plotted it will be seen 

 that the value of the coefficient approaches "003660 when the pressure becomes 

 small. This result is in agreement with theory. The value of the coefficient at 

 normal pressure is •003667, and if we apply this result to the calculation ol 

 corresponding temperatures on the two scales we find : — ■ 



Temperature on constant volume scale . . . — 190°C. 

 Temperature on constant pressure scale . . . — 190°^5 C. 



6. Note on the Variation of the Specific Heat of Water. By Professor 

 H. L. Callendar, F.Ii.S.—See Reports, p. 34. 



7. The Laws of Electrolysis of Alkali Salt Vapours. By Harold A. 

 Wilson, D.Sc, M.Sc, B.A., Clerk-Maxivell Student, Cambridge 

 University. 



The method employed in the experiments described in this paper was the 

 following: — A current of air, containing a small amount of salt solution in 

 suspension in the form of spray, was passed between two concentric cylinders of 

 platinum heated in a gas furnace. These cylinders were maintained at a large 

 difFerence of potential by means of a storage battery, and the current between 

 them through the stream of air and salt vapour was measured at various tempera- 

 tures and with diflerent E.M.F.'s. 



It was found that above 1300° C. and with more than 800 volts P.D. the 

 current through the salt vapour became ' saturated,' that is, it was not increased 

 appreciably either by raising the temperature or increasing the E.M.F. applied. 



This saturation current was measured for a number of different alkali metal 

 salts. The table on the next page contains the results obtained. 



It will be seen from the above results that the product EC is approximately a 

 constant for solutions of the same concentration. Also EC is ten times greater 

 with solutions of 10 grams in a litre than with solutions of 1 gram in a litre. 



It follows therefore that the saturation current through an alkali salt vapour 

 is (1) proportional to the amount of any one salt passing between the electrodes, 

 and (2) inversely proportional to the electrochemical equivalent of the salt 

 sprayed. 



These results are exactly analogous to Faraday's Laws of Electrolysis for 



