[ «5 ] 



XLIX. Note on the Electric Conductivity of Hot Gases. 

 By Dr. Svante Akkhenius*. 



THE following lines have reference to Prof. J. J. Thomson's 

 letter in the Philosophical Magazine for February 1891, 

 p. 135. The question at issue between Prof. Thomson and 

 myself is whether gaseous hydrochloric, hydrobromic, and 

 hydriodic acids (and, still more, chlorine, bromine, and iodine) 

 conduct electricity electrolytically at high temperatures, or 

 only conduct in consequence of dust-particles suspended in 

 them. Prof. Thomson's view is that the hydrochloric-acid 

 molecules (HC1) decompose partially at high temperatures 

 into atoms of hydrogen and chlorine (H and CI) which are 

 charged with electricity, positive or negative, according to 

 Faraday's Law, i. e. are charged with 96 coulombs per milli- 

 gram-equivalent. Crafts f has shown that such a decomposi- 

 tion, which would be recognized by its effect on the vapour- 

 density, does not take place at the temperature of Prof. 

 Thomson's experiments (yellow heat, about 1100° C). It is 

 conceivable, however, that very little decomposition might 

 suffice to cause the electrolytic conduction ; and so we will 

 assume in the meantime that there is a slight dissociation of 



+ 

 HC1 into H and CI, not measurable by other means. It 

 must be clearly understood that this dissociation is assumed 

 for the exclusive purpose of explaining the conductivity, and 

 is not, as one might imagine from Prof. Thomson's account, 

 suggested by other circumstances. 



if such a dissociation takes place, it need not in any way be 

 (perceptibly) dependent on the quantity of hydrogen (H 2 ) 



+ - 

 present. The equilibrium is one between H, CI, and HC1; 

 just as it is between PC1 3 , Cl 2 , and PC1 5 in Prof. Thomson's 

 example. Whether the presence of H 2 will affect the quantity 



of H (and CI) or not, depends entirely on whether there is anv 



+ - 



interaction between H 3 and H (or CI) of sufficient extent to 

 have an appreciable effect on the above equilibrium. This 

 certainly cannot be asserted a priori^ but must be considered 

 an accessory hypothesis introduced to explain Prof. Thomson's 

 observation that the conductivity of HC1 is diminished by the 

 presence of H 2 . 



* Communicated by the Author. 



t Comptes Rendus, xc. p. 311 : — " On a trouve dans les experience* 

 suivantes une densite norinale pour l'acide chlorhydrique a la plus haute 

 temperature du fourneau "—4. e. 1400 u -1500° 0. 



