Conductivity produced by Heating Salts. 



743 



for the ions from bismuth iodide. It will be seen that 

 between pressures 50 and 25 mm. of mercury the product 

 does not vary much. There is evidence of simplification 

 taking place between pressures 90 mm. and 50 mm. 

 Langevin * has shown that PxV remains very nearly 

 constant for positive ions produced by Rontgen rays between 

 pressures 75 mm. and 1435 mm. of mercury, thus showing 

 that between those pressures the constitution of those positive 

 ions remains the same. The change in P.V at the lower 

 pressures I cannot account for. The manner in which the 

 velocity changes with the temperature at low pressures when 

 the pressure remains constant is shown in fig. 4, in which the 

 temperatures are plotted for abscissae and the velocities for 

 ordinates. 



It will be seen that in all cases, except that of zinc iodide 

 at a pressure of 10 mm. of mercury, there is a very rapid 

 rise in the velocity at a temperature between 205° C. and 

 210° C, indicating that a simplification of the ion has taken 

 place at that temperature. 



Phillips f has found a linear relation to hold between the 

 velocity and temperature for ions produced by Rontgen rays 

 between —64° C. and 138° C. 



Velocities of the negative ions. — The velocity of the negative 

 ions was measured in the case of those from barium, calcium, 

 and zinc iodides ; and the results obtained from all these 

 sources under the same conditions of experiment were practi- 

 cally identical. These are shown in the following tabulated 

 list. The velocities are all for temperature 215° C, and are 

 given in cms. per second for one volt per cm. 



Pressure 



in mm. of 



mercury. 



Zinc 

 iodide. 



Calcium 

 iodide. 



Barium 

 iodide. 



Pressure X Velocity 



in case of 



Zinc iodide. 



10 



20 



30 



35 



1-05 

 "06" 



"42" 



•35 



"•21* 



1-10 



'•56* 



•33" 

 •22 



"2 



1-11 

 •74 



"45" 

 '•29" 



1105 



16-80 



16-80 

 17-50 



16-80 



40 



50 



60 



80 





In this case also it will be seen that, with the exception of 

 the velocity at 10 mm. pressure, the values of (Pressure x 

 Velocity) are fairly constant. 



* Theses Universite de Paris, p. 190. 

 f Proc. Roy. Soc. vol. lxxviii., 1906. 



