NEGATIVE ELECTRICITY PROM HOT CALCIUM AND FROM LIME. 



157 



made in which the calcium wire was warmed sufficiently to expel some gas from it, 

 but not to a high enough temperature to cause it to volatilize on to the platinum. 

 The evolved gas was then absorbed in the potassium-sodium alloy, and the leak from 

 the platinum strip in helium gas was again tested. It was found to be the same as 

 before the calcium wire had been heated. 



The negative leak from the calcium-covered strip was found at several tempera- 

 tures. The observed values are given in the following table. The potential 

 difference between the electrodes was 40 volts, and the gas pressure, as before, 

 3-236 millims. 



TABLE IV. 



Mean value of Q = 7 -29 x 10~ 4 . 



The observed currents in the table are plotted against the corresponding temperatures 

 in fig. 4. The unit of current is successively multiplied by ten in passing to the right 

 from one curve to the next. 



It will be seen that the curves obtained are exactly similar to those given by 

 platinum.* 



The observations of the negative leak from calcium were made as quickly as 



* See RICHARDSON, 'Phil. Trans.,' A, vol. 201, p. 497. 



