178 Dr. 0. Sheard on the Positive 



corpuscles than B ; hence A may again become positively 

 and B negatively charged. We should thus get a state, 

 dependent upon temperature, in which the number of 

 recombinations in unit time would approach equality to the 

 n amber o£ molecules dissociated in that time. The greater 

 the ease of getting the corpuscles out of B, the less the 

 amount of positive, or positive producing, material there 

 would be. This explanation would account for the marked 

 decrease in the positive ionization, subsequently obtainable 

 at lower temperatures, when ihe wire is heated from 756— 

 820° C. 



The maximum positive thermionic emission obtained after 

 heating at 654° C. can be explained in an analogous manner 

 by assuming a substance capable of dissociation in this lower 

 temperature range into + C and — D ions. The maximum 

 positive emission would exhibit itself after heating at a tem- 

 perature such that the negative ions begin to lose electrons. 

 Further increase of temperature would cause a greater 

 liberation of electrons, and the consequent neutralization of 

 the positive ions within the wire. No electronic emission is 

 detectable at these temperatures since the electrons do not 

 possess sufficient kinetic energy to enable them to escape 

 from the wire. Hence heating the wire under negative 

 potential at temperatures below 760° C. — the temperature at 

 which negative currents were detected in these experiments- 

 would have no effect in increasing the positive emission 

 subsequently obtainable, at least until temperatures ap- 

 proaching 760° C. are used. These latter effects are 

 discussed in Section VII. 



This view does not preclude the possibility of secondary 

 chemical reactions within the wire or between a hot wire 

 and a salt at its surface. The proof seems conclusive that 

 potassium and sodium salts, present as impurities in metals, 

 constitute the source of positive emission. If so, sulphates 

 of these bases might be expected ; upon decomposition the 

 acid radicle may combine under temperature with the metal 

 of the wire ; hence corpuscular and not ionic emission would 

 occur. 



Some observations were made on the decay of the positive 

 currents with time when the wire was earthed and heated for 

 10 minutes and the emission then tested at the temperature 

 previously employed. (See note.) The tabulation given in 

 Table II. shows the method of procedure. The data show 

 that heating at 765° C. for 10 minutes and reducing to 

 738° C. produced an increase of positive ionization ; heating 

 at 786° C., however, gives a much smaller current at 765° C. 



