590 Electrification due to Heating Aluminium Phosphate. 



XL Rectifying Effect of the Heated Salt. 



Owing to the great velocity with which the positive ions 

 are shot off from the heated salt when the pressure is very 

 low, it was thought that such a tube as shown in fig. 1 could 

 be used for rectifying alternating currents providing the 

 temperature of the salt was kept within certain limits. It 

 has been found by various experiments that it can be so 

 used. 



Further work on this point is in progress. 



XII. Summary. 



(i.) The decay of the current due to positive ions obtained 

 by heating aluminium phosphate has been investigated, and 

 it is found that the curve connecting current and time can 

 be represented by a formula of the type 



(ii.) During the first part of the decay, the nature of the 

 surrounding gas and the water contained by the salt have an 

 important influence. When the steady state is reached the 

 gas has no apparent influence, but water still temporarily 

 increases the activity. 



(iii.) The discharge produced by an induction-coil tempo- 

 rarily increases the current which is carried by the positive 

 ions. 



(iv.) When the temperature is kept constant, it is found 

 that for each temperature there is a definite pressure at 

 which the current is a maximum. This pressure being- 

 lower, the higher the temperature. 



(v.) The Richardson formula I = a6*e~Q 129 can be used to 

 express the relationship between the current and absolute 

 temperature when the pressure is kept constant. 



(vi.) A value is obtained for e/m which indicates that the 

 smallest positive ions present at the lowest pressures must 

 be of a magnitude comparable with that of the hydrogen 

 atom. 



(vii.) The high velocity of tbe ions at low pressures, aud 

 also the fact that some escape with great velocity even when 

 no external field is applied, leads one to expect that a tube 

 in which some aluminium phosphate is heated might be of 

 use as a rectifier for alternating currents. It can be so used. 



(viii.) The experiments (a) with varying pressures at con- 

 stant temperature, (b) at atmospheric pressure in which a 

 current is produced after all the ions are apparently removed, 



