398 Mr Bevan, On the Temperature Effect in the combination 



The Temperature Effect in the combination of Hydrogen and 

 Chlorine under the influence of Light. By P. V. Bevan, M.A., 

 Trinity College. 



[Read 15 February 1904.] 



It has been recognized for some time that the accelerating 

 influence of rise of temperature on chemical actions, which are 

 produced by the action of light on the reacting substances, is 

 very considerably less than the corresponding effect in actions 

 where the influence of light is not required for the action to take 

 place. With these facts in view, it occurred to the author that 

 an investigation into the increase in rate of combination of 

 Hydrogen and Chlorine caused by an increase of the temperature 

 at which the action takes place might throw some light on the 

 mechanism of this action. The combination being conditioned 

 by the presence of water vapour in the mixture of the two gases, 

 it was thought that, as the specific influence of temperature on 

 the velocity constants of the action is probably small for small 

 ranges of temperature, the comparatively rapid change of water 

 vapour pressure with rise of temperature might lead to changes 

 in the rate of combination which would enable some insight to 

 be obtained into the part played by the water vapour in the 

 action. The results to be described do not throw any very clear 

 light on this general question, but they are of interest as in- 

 dicating that the action is not of a simple character, and that 

 the relations of van 't Hoff and others concerning the change of 

 velocity constants with temperature do not hold in this particular 

 action. It will appear later that the assumption of the formation 

 of molecular aggregates, or of some special kind of molecules, as 

 a preliminary phase of the action will enable us to understand the 

 phenomena at any rate qualitatively. 



The method adopted for the investigation was that of Bunsen 

 and Koscoe, which has proved the best possible arrangement for 

 studying this particular action. The combination was made to 

 occur in a glass bulb containing a little water in its lower part. 

 As hydrochloric acid is formed it is absorbed by the water in the 

 bulb, and the consequent diminution of volume of the gas is 

 observed by the motion of an index of water in a capillary tube*. 

 In the experiments now described the bulb in which the com- 

 bination takes place was arranged so as to hang in a water bath 

 which itself stood in another bath which was kept at the required 



* For a complete description of the apparatus used and the method of generating 

 the mixture of Hydrogen and Chlorine see a paper by the author in Phil. Trans. 

 A. 202, p. 71. 



