﻿140 Mr. Clinton J. Davisson : Hole Played by Gases 



example, that these results contain any direct evidence against 

 the hypothesis that, in some cases, all or a part o£ the ther- 

 mionic current is carried by carbon monoxide. Horton * 

 found that in the cass of a sample of aluminium phosphate 

 which he investigated, the electrical emission was accom- 

 panied by an emission of carbon monoxide, from which he 

 has inferred that the carbon monoxide was carrying the 

 current. Neither is it legitimate from these results, which 

 are for very low gas pressures, to conclude that no part of 

 the current is carried by atoms or molecules of the gas in 

 contact with the salt. Garrett f and also Horton J found 

 that at constant temperature the electrical emission depends 

 in a very marked way upon the pressure and nature of this 

 gas. Garrett concluded from the nature of this dependence 

 that heated salts emit neutral doublets which are split apart 

 by collision with gas molecules. Horton (I. <?.) has raised 

 what appear to be valid objections to this hypothesis and has 

 concluded that the gas atoms or molecules take an active 

 part in the transfer of charge. 



The present paper includes an account of various experi- 

 ments which have been carried out for the purpose of testing 

 these special hypotheses by determinations of the specific 

 charge of the thermions from salts under conditions similar to 

 those obtaining in the experiments of Garrett and of Horton. 



The method by which these determinations have been 

 made is identical with that described in the paper above on 

 44 Positive Thermions from Salts of Alkaline Earths/' 



The relation between the electrical and gas emissions was 

 taken up in connexion with the experiments on strontium 

 chloride described in the paper mentioned above. It was 

 noticed during these experiments that the gas pressure in the 

 apparatus was higher when the strip was heated than when 

 it was not. In a case investigated the pressure in the 

 apparatus when the strip was not heated was r6 x 10" 5 mm. 

 by the McLeod gauge. With the strip at a temperature of 

 approximately 1000° 0. the pressure increased and became 

 uniform at 99 x 10~ 5 mm. The Gaede pump in connexion 

 with the apparatus was running continuously. 



In order to determine, if possible, the nature of this gas 

 the pumping wa s discontinued while the strip was being- 

 heated and the evolved gas allowed to accumulate. After 

 ten or fifteen minutes the part of the gas in the bulb of the 

 McLeod gauge was compressed into the capillary and 



* Pioc. Rov. Soc. A. vol. lxxxiv. no. 572, Dec. 1910. 



t Phil. Mag. Oct. 1910. . - 



| Camb. Phil. .Soc. Troc. vol. xvi. part i. Feb. 1911. 



