102 Sir H. Davy on the Relations 



of gas, which is probably oxygen, on the platinum in contact 

 with the alkali ; and that the acid tends to circulate towards 

 the negative surface, and the alkali towards the positive, is 

 shown by the circumstance of the i-apid neutralization of the 

 two menstrua, though separated by asbestus moistened in 

 distilled water. 



VI. Of combinations consisting of two conductors of the mcn-e 

 perfect class, and o?ie fluid. 



The order in which metallic bodies exhibit electricities on 

 contact, as is well known, is intimately connected with their 

 relative oxidability, the most oxidable metal being positive 

 with respect to all those below it. This law extends likewise 

 to the newly discovered bases of the alkalies and earths. 

 Potassium and sodium, as I have found by bringing them in 

 contact with zinc in a concentrated solution of alkali, are ap- 

 parendy as much positive with respect to this body, as zinc 

 is with respect to platinum and gold. 



There is not however any inherent and specific property in 

 each metal which gives it the electrical character ; it depends 

 upon its peculiar state — on that form of aggregation which 

 fits it for chemical change. Thus, zinc in amalgamation with 

 mercury is positive with respect to pure zinc, and the amal- 

 gam of tin is in the same state with regard to tin ; and the 

 metals of the fixed alkalies in amalgam give the highest po- 

 sitive energy to a mass of mercury some thousands of times 

 their weight. 



In general, the electricities developed by metallic contact 

 are of a stronger kind than those resulting from the contact 

 of metals with fluids, so that they are not capable of being 

 chanf ed by them. For instance : zinc in acid is positive with 

 respect to all other metals below it in degree of oxidability, 

 thouo-h they are placed in alkalies or solutions of sulphurets : 

 there are however exceptions ; for instance, with regard to 

 tin, which, when in a strong solution of potassa, is positive to 

 zinc, in an acid solution ; and with respect to iron, which, 

 though positive with regard to copper in all acid or neutro- 

 saline fluids, is negative to it in solution of sulphurets or of 

 alkalies. The electro-motion in these instances produced by 

 the contact of the fluids prevailing over that produced by the 

 contact of the metals. 



And knowing the energies of the acid and alkaline fluids, 

 it is easy to apply them so as to diminish or enhance the elec- 

 trical effects developed by metallic contact. 



If, for instance, in a combination containing zinc and pla- 

 tinum, we use two fluids, and place the acid in contact with 



the 



