378 Mr. W. K. Bridgman on the Theory of the Voltaic Pile. 



the fluid is not sufficiently powerful to cause sensible action at the 

 surfaces in contact and occasion the decomposition of water by 

 the oxidation of the metal" (Exp. Res. 893). 



Again, in reference to a cylinder of amalgamated zinc placed 

 inside a double cylinder of copper, and the two then inserted 

 within ajar of dilute sulphuric acid, it is asserted that "being 

 thus arranged there was no chemical action whilst the plates 

 were not connected" (957) j and "a battery constructed with 

 the zinc so prepared (that is, amalgamated), and charged with 

 dilute sulphuric acid, is active only whilst the electrodes are con- 

 nected, and ceases to act or be acted upon by the acid the instant 

 the communication is broken" (1000). 



The very decided manner in which the assertion, that no che- 

 mical action takes place unless the dissimilar metals of the battery 

 be put into communication, is made, and the frequency with which 

 the belief in it is reiterated in various forms, make it appear 

 that this supposed fact was considered of some importance in 

 connexion with the conclusions arrived at. If, however, it be put 

 to the test of examination, it will be found to receive a direct 

 negative from experimental evidence and shown to be altogether 

 a fallacy. 



A rod of absolutely pure zinc, 3J inches long and weighing 

 487 grains, after being thoroughly amalgamated and drained, 

 was placed half its length in cold dilute sulphuric acid (one part 

 pure acid to ten of water), and the other half exposed to the at- 

 mosphere in the same position as the ordinary plates of a battery. 

 In a very short time bubbles of hydrogen made their appear- 

 ance over the whole of the surface exposed to the acid, and after 

 forty-eight hours the zinc was fouud to have lost upwards of two 

 grains in weight. This loss, however, was by far the least im- 

 portant part of the results obtained. The immersed portion of 

 the metal had not been acted upon uniformly over its entire sur- 

 face, but the action had been greatest at the surface of the liquid ; 

 at the same time the exposed portion had become covered with 

 patches of crystalline sulphate of zinc, high and dry upon the 

 projecting part of the metal. In addition to the fact of chemical 

 action having been exerted between the metal and the acid and 

 the water decomposed, there is the further evidence of the metal 

 having been polarized. 



In order to render the effect more apparent, the experiment 

 was repeated with copper instead of amalgamated zinc, as the 

 colour of the crystals and the colouring of the acid afford more 

 conspicuous evidence of the results which are being produced. 



A piece of stout copper wire was then similarly placed in acid ; 

 the latter very soon gave signs, by the colouring it received, 



