525 



Rev. T. R. Robinson, D. D., read a paper on the effect 

 of Heat in lessening the Affinity of the Elements of Water. 



The author referred to the experiments of Mr. Grove on 

 the decomposition of water by the action of incandescent pla- 

 tinum; and, after noticing the objections which were urged 

 against its being caused by heat, detailed results which he 

 had obtained at a much lower temperature, and which ap- 

 peared to him to accord with that hypothesis. 



Proceeding on the theory of the voltaic circuit, which 

 Ohm has given, he investigated the diminution of electric 

 intensity, which is caused by placing in the circuit a cell where 

 water is subjected to voltaic decomposition, and shewed that 

 it is equal to the affinity of platina for oxygen minus twice that 

 of hydrogen for oxygen, or 



e — op — 2ho. 



This quantity e can be measured by the instruments and pro- 

 cesses described by Mr.Wheatstone in the Philosophical Trans- 

 actions for 1843, with some modifications, which, in the au- 

 'thor's opinion, increase their accuracy. After describing the 

 apparatus he used, he finds for the value of e, 



At the temperature 61° . . . e =598.9 . . . 12 obs. 



135°.4 567.6 ... 13 



20l°.3 531.0 ... 12 



These give, for an increase of temperature of 1 00°, the decrease 

 of the affinity of the oxygen and hydrogen of water =. 23.2. The 

 author applies to this result the theory of probabilities, which 

 has so much advanced astronomical and physical science ; and 

 finds the chances to be 10,000 to 1 that it is not all error of 

 observation. 



It might be objected, that this diminution of e is due to 

 the expansion of the gases by heat enabling them to escape 

 more freely from the electrodes. This was tested by placing 



