Ionization from Heated Platinum. 187 



that no increased positive emission could be gotten unless the 

 wire had been previously heated at a temperature such that 

 negative currents were obtainable. 



Both rows of figures also show the maximum emission 

 under steady conditions at 690-700° 0., in general agreement 

 with the curves of fig. 1. 



These researches have naturally suggested the carrying 

 out of similar experiments with salts. Of particular interest 

 would be the effects obtained with salts of sodium and 

 potassium. (Such work is now in progress. 



Conclusions. 



As a brief summary of the paper, attention is called to : — 



(1) Increase of positive thermionic currents produced in 

 high vacua (a) by heating a wire under zero potential at 

 higher temperatures than at which the ionization is subse- 

 quently measured, and (7>) by heating the wire under negative 

 potential at such temperatures as to discharge negative 

 electricity. (Section I.) 



(2) A detailed examination of the positive currents pro- 

 duced by method (a) cited above in dry air at atmospheric 

 pressure. Maximum effects were obtained after heating at 

 654° C. and 756° 0. when tested at 628° 0. The intimate 

 connexion between the decrease of positive thermions pro- 

 duced at temperatures above 750° 0. and the liberation of 

 electrons was pointed out and a general theory given to 

 account for the experimental results obtained. (Section III.) 



(3) Similar results were obtained by heating the wire in 

 the reducing portion of the Bunsen flame. The role played 

 by hydrogen in producing an increased positive emission is 

 discussed and the theory advanced that hydrogen, through 

 its affinity for electrons, accelerates the production of positive 

 ions by (a) inhibiting recombination of positive and negative 

 ions, and (b) by removal of electrons. (Section IV.) 



(4) A decreased rather than increased positive ionization 

 was occasioned by heating in carbon dioxide. A possible 

 explanation is offered. (Section Y.) 



(5) An investigation of the decay with time of the posi- 

 tive currents at different temperatures showed the existence 

 of at least two sources of ions ; the first giving decay effects 

 according to an exponential law, the second showing an 

 increase to a maximum followed by subsequent decay with 

 time. (Section VI.) 



Physical Laboratory, 



Ohio State University, Columbus, O. 

 March 1st, 1914. 



