406 Sir Humphry Davy on the relations of 
And knowing the energies of the acid and alkaline fluids, 
it is easy to apply them so as to diminish or enhance the 
electrical 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 zinc, and the alkali with the platinum, the effect will be 
exceedingly feeble compared with that produced if the order 
be reversed, and the zinc be in contact with the alkali, and 
the platinum with the acid. 
The chemical changes taking place in combinations of this 
kind are always such as tend to restore the equilibrium, the 
hydrogen and the alkaline body always passing to the nega- 
tive, and oxygen and the acid to the positive metal. 
There is no instance of continued electro-motion except 
in cases where chemical changes can take place, for even 
De Luc's or Zamboni’s columns do not act when quite dry, 
and the silver in combinations of this kind, when the nega- 
tive metal is gold, is uniformly found tarnished : for the 
exhibition of electricities of tension, however, a very slight 
chemical action is sufficient, as the quantity of electricity 
required to give repulsion to light bodies is exceedingly small; 
but to form electro-magnetic combinations the chemical agents 
must be of an energetic kind. 
As most of the fluids which act powerfully in voltaic com- 
binations containing water, or oxygen and hydrogen, it has 
been suspected that these principles were essential to the 
effect ; this however does not seem to be the case, for I found 
zinc and platinum formed powerful electro-motive circles in 
fused litharge and fused oxy-chlorate of potassa, which are not 
