Disintegration in a Vacuum Tube. 427 



presence of hydrogen facilitates the production of a thermionic 

 current. 



The fact that the disintegration vanishes at the normal 

 cathode-fall is one of considerable theoretical interest and 

 importance, but discussion of this and other points is reserved 

 until further data have been obtained. 



Summary. 



Some of the factors which govern the disintegration of a 

 platinum cathode in a vacuum tube have been investigated, 

 with the following results : — 



1. Provided that a constant cathode-fall is maintained : 



(a) Considerable changes in pressure have no influence 

 on the amount of disintegration for a given current and 

 duration of discharge ; 



(Ij) New and old cathodes of the same area disin- 

 tegrate practically to the same extent under the same 

 conditions of current and duration of discharge ; 



(c) The rate of disintegration for a given current 

 density is constant throughout discharge. Thus it is 

 not affected by the removal of gases from the surface of 

 the cathode by previous discharge. 



2. The influence of the cathode-fall of potential on the 

 rate of disintegration has been investigated at low values of 

 cathode-fall. No simple relationship (such as exists at high 

 values) has been observed. The rate of disintegration 

 appears to vanish at the normal cathode-fall. 



3. The linear relationship which exists between current 

 density and rate of disintegration at small current densities 

 and high cathode-falls does not hold in the general case. 



4. Preliminary work on the influence of the nature of the 

 gas shows that at low values of cathode-fall there is no 

 appreciable difference between the rates of disintegration in 

 hydrogen and air under similar conditions. 



5. Certain theoretical considerations are advanced in 

 connexion with some of the above results. 



The above experiments were carried out in the Physical 

 Laboratory of the University of Bristol. Our thanks are 

 due to Mr. J. B,. Boon, B.Sc, who rendered valuable 

 assistance in the observations throughout the latter part of 

 the work. We were further aided in the work by a grant 

 from the Research Fund of the University Colston Society. 



January 10th, 1914. 



