On Thermo chemical Constants. 53 



(b) Glass and Mercury. deflection. 



Dipped once quietly + 6 to + 10 



20 rapid splashes — 7 



50 „ „ - 1 



60 „ „ - 6 



90 „ „ +4 



100 „ „ - 3 



The above results, it will be seen, are very irregular, owing- 

 no doubt to the fact that all the circumstances of contact 

 could not be accurately known. These irregularities, and 

 especially the variable sign of the electrification, make it clear 

 that the effects are not due to a true and definite contact 

 E.M.F., but are dependent in some degree on the manner in 

 which the surfaces are brought together and separated. The 

 experiment of Canton in 1753 (where the rough and polished 

 parts of a glass tube became oppositely electrified when 

 rubbed with the same cloth) seems to point in the same 

 direction. 



Professors Ayrton, Schuster, S. P. Thompson, and J. Perry 

 discussed the points raised, and it was considered that direct 

 experiment on contact electromotive force in a very perfect 

 vacuum could alone decide the question. 



This experiment seems almost as impracticable as a direct 

 measurement of the size of a molecule. Yet the two ques- 

 tions may be equally capable of solution by inductive reason- 

 ing. The question is whether the reasoning given above is or 

 is not conclusive. — C. Y. B. 



YII. On Thermo chemical Constants. By Spencer Umfre- 

 ville Pickering, M.A. Oxon, Professor of Chemistry at 

 Bedford College* . 



THE existence, amongst thermochemical data, of certain 

 quantities which are constant, or nearly constant, cannot 

 be denied. 



AVe have in the first instance the fact that the heat of 

 neutralization is in the majority of cases independent of the 

 nature of the acid and the alkali concerned ; and a simple 

 explanation of this may be found, as I have shown ((Jhem. 

 Soc. Trans. 1887, p. 593), in the complete saturation of the 



* Communicated by the Author, having been read before the Chemical 

 Society. 



