316 Mr. Smee 07? the Galvmiic 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, ceteris loaribus, 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 



