316 Mr. Smee on the Galvanic Properties of Metals. 
the public a valuable battery, no time is lost, that others may 
extend and improve the new principle about to be detailed. 
With regard to the metallic elementary bodies, their pro- 
perties have been investigated so frequently, and to such an 
extent, that it may seem unnecessary to draw attention again 
to them ; but two circumstances influencing their action have 
never been noticed. It is well known that the positive metal 
should be the most readily acted upon by the solution, and 
the negative the least, and the further these are apart, the 
more forcible will be the battery ; thus, creteris paribus.^ plati- 
num and zinc are more powerful than iron and zinc ; but if a 
circuit be made of a piece of smooth platinum and zinc it will 
sometimes happen that the effect is less than when a circuit is 
formed by a similar piece of iron. Now this appears at first 
sight paradoxical, though it can in many instances be easily 
explained ; for if the platinum be carefully examined, it will 
be seen that the acid solution does not really wet the platinum, 
but runs off from the greater part of the surface, as metallic 
mercury does from glass. In this state, a piece of platinum 
having a surface of thirty-two square inches, formed into a 
battery with amalgamated zinc and connected with a magnet, 
supported three-quarters of a pound through five thicknesses 
of paper ; when the same piece of platinum was heated or 
dipped in nitric acid and afterwards well washed, it supported 
a similar weight through twelve thicknesses of paper, thus 
being less powerful than iron in the first instance, and more so 
in the second. In the same way, silver supported under the 
like circumstances, the keeper of a magnet through three layers 
of paper : on being heated and again wetted, the attractive 
force was exerted through nine thicknesses of paper, but no 
additional power was gained by removing the surface of the 
silver by nitric acid. The metals in these cases appear to 
become coated with a film of air, which effectually prevents 
the contact of the fluid. This is also seen in the various forms 
of charcoal, which after ignition are very powerful, but lose 
much of their force if long exposed to the air; their energy 
however is restored upon their being again heated. 
As in the experiments just detailed, and in those which I 
am about immediately to describe, the relative powers of the 
arrangements have to be considered, it will be proper to men- 
tion in what way the results were obtained. A soft iron horse- 
shoe magnet was suspended, round which covered wire in 
communication with the poles of the battery was wound : the 
keeper, which weighed three quarters of a pound, was sepa- 
rated from the poles of the magnet by as many layers of thin 
blotting paper as could be used without its falling ; thus with 
