SIR, 

 <e - 



[ 86 ] 



XIII. Mr. Davy's Theory. 

 To Mr. Tilloch. 



1 thank you for your early insertion of my former com- 

 munication, as by that means I was favoured by Mr. Davyfs 

 observations on it in his lecture yesterday. 



" It seems that I misunderstood him : it is fit therefore 

 that I should state that T did so. He did not assert (in reference 

 to the experiment of the decomposition of the sulphate of 

 potash) that the sulphuric acid and the potash repelled each 

 other in consequence of being in opposite states of electri- 

 city, but in consequence of being brought into the same state, 

 " I had understood him to say that the decomposition 

 took place in consequence of the natural electricities of* the 

 sulphuric acid and the potash being reversed by means of 

 the Galvanic apparatus ; and I was less disposed to suspect 

 that I was wrong, from observing the following passage in 

 the Bakerian Lecture for 1807, which seemed to me to con- 

 vey the same doctrine : e In the decompositions and changes 

 presented by the effects of electricity, the different bodies 

 naturally possessed of chemical affinities appear incapable of 

 combining, or of remaining in combination, when placed in a 

 state of electricity different from their natural order.' Philo- 

 sophical Transactions, 1 807, p. 33; and as, in the experiment 

 alluded to, both the sulphuric acid and potash seemed to me 

 to be placed in a state of electricity different from their na- 

 tural one, I was by this means confirmed in my mistake. 



ff That I did misunderstand him, however, I am amply sa- 

 tisfied by Mr. Davy's declaration, which is moreover shown 

 by the following passage, which, had it occurred to me at the 

 time, would probably have pointed out my error : it refers to 

 the theory of the decomposition of the fixed alkalies, and is 

 as follows : 'The oxygen being naturally possessed of the ne- 

 gative energy, and the basis of the positive, do not remain in 

 combination when either of them is brought into an electri- 

 cal state opposite to its natural one.' Phil. Trans. 1808, p. o, 

 " Hence, therefore, we are to understand, that in the expe- 

 riment of the sulphat of potash to which I have so often re- 

 ferred, 



