160 



DR. FRANK HORTON ON THE DISCHARGE OF 



time through the tube containing the sodium-potassium alloy. The pressure of the 

 helium was, as in the case of the calcium cathode, 3 '236 millims. 



TABLE V. 



Mean value of Q = 9-58 x 10*. 



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



temperatures in fig. 5. The curves obtained are of the 

 usual form for the negative leak from glowing solids. 



By comparing Table V. with Table IV. it will be seen 

 that the negative leak from lime is enormously greater 

 than from metallic calcium under the same conditions, 

 the leak from a lime cathode at 950 C. being about the 

 same as the leak from calcium at 1400 C. This is 

 contrary to what we should expect on the supposition 

 that the negative leak is due to the escaping of the 

 corpuscles from the cathode, for the presence of an atom 

 of oxygen in the molecule of lime would hinder, by its 

 attraction for negative electricity, the escape of the 

 corpuscles, and we should expect, in consequence, that 



the negative leak from lime would be less, under the 

 Fig. 5. Negative leak from lime ,... ,. , , AIJ.U 



same conditions of temperature and pressure, than the 

 in helium at a pressure of . 



3 -236 millims negative leak from the same amount of calcium in the 



metallic state. 



The values of the constant Q, deduced from successive pairs of observations, are 

 given in the last column of Table V. 



700^ 800 900 



Temperature centigrade 



