Positive Electricity from Hot Bodies. 639 



(Proc. Roy. Soc. Dec. 1910), support this view. Further, 



p 

 the value of — found by Garrett, I. c, for some of the ions 



emitted when aluminium phosphate is heated on platinum is 

 consistent with the view that hydrogen ions are also emitted 

 from hot platinum. 



Now if we suppose — as I think we are justified in doing — 

 that even the purest platinum contains traces of carbon, the 

 water effect can easily be explained. When the platinum is 

 heated in the presence of water vapour, the water will be 

 decomposed with the formation of carbon monoxide and 

 the liberation of hydrogen. This may occur even at tempe- 

 ratures considerably below that at which the positive leak 

 begins to be appreciable. These gases will naturally diffuse 

 into the platinum and re-emerge under suitable conditions 

 in the form of positive ions. There is also the further possi- 

 bility that water may accelerate catalytically the production 

 of carbon monoxide when platinum is heated in air. 



Positive Leak from Hot Aluminium Phosphate. — Both Horton 

 and Garrett heated the aluminium phosphate on platinum. 

 The salt was made into a paste with water, and moreover 

 contains in any case a large amount of water. As this water 

 will affect, temporarily at any rate, the activity of the platinum, 

 the question naturally arises : What part of the discharge 

 from the hot phosphate are we entitled to ascribe to the salt 

 itself ? Even when it has been heated so long that the effect 

 due to the presence of water has died down, it is still con- 

 ceivable that the salt may facilitate in some way the escape 

 of ions from the platinum. I failed to observe any positive 

 discharge from aluminium phosphate when the latter was 

 heated on a Nernst filament, the temperature of which was 

 very much higher than that employed in the experiments 

 with a platinum wire. The experiment was carried out both 

 on a Nernst filament provided with the usual heating arrange- 

 ment and on one not so provided. In the former case the 

 galvanometer showed an appreciable deflexion (20 to 30 scale- 

 divisions) while the heater ivas in operation. This deflexion 

 diminished to zero immediately the heater was cut out. It 

 was therefore due to the platinum wire of the heater. While 

 the Nernst filament was glowing no deflexion of the galvano- 

 meter could be observed. The experiment was done under 

 conditions as closely resembling those in which a platinum 

 wire was used as possible. 



It seems quite likely that aluminium phosphate, at any 

 rate when prepared from aluminium acetate, may contain 

 traces of carbon, and therefore some part of the positive 



