Two Fluids, and of Two Metals not in Contact. 491 



on long use in acids, so that plates whicli fresh were nearly ho- 

 mogeneous, acquired with time a considerable heterogeneity. 

 Filing the surfaces thoroughly bright was the sole means of 

 restoring them to their original state. Nevertheless I em- 

 ployed in the further progress of my inquiries, and on the repe- 

 tition of experiments, only distilled zinc, to be more certain. 



For a similar reason I also had recourse to amalgamated 

 zinc. Plates of ordinary zinc, possessing a very considerable 

 degree of heterogeneity, lose it in fact by amalgamation (pro- 

 duced by rubbing them with dilute sulphuric acid and mercury), 

 and become almost perfectly homogeneous ; but they remain so 

 only immediately after this operation, so long as the surface of 

 the metal is, as it were, fluid. After some time the amalgam 

 hardens to a crystalline mass, generally sooner or to a greater 

 extent on one plate than on the other, and then the hetero- 

 geneity again makes its appearance. The plate with the fluid 

 surface is in acids positive to that with the crystalline dull 

 appearance. By rubbing the latter with mercury the hetero- 

 geneity may again be suppressed. Although it is in our power 

 to bring amalgamated zinc plates to any degree of homogeneity 

 previous to each experiment, yet it did not appear advisable to 

 employ solely such, as amalgamated zinc must in a certain degree 

 be regarded as a different metal from ordinary zinc, and its easy 

 liabihty to change might produce disturbances. The sequence, 

 however, showed that in general it affords the same results as 

 the non-amalgamated zinc, and in numerous cases possesses 

 considerable advantages over the latter. 



Besides this, no precaution was neglected that is indispen- 

 sable in this kind of experiments*; for instance, the clean- 

 sing of the plates after each experiment, by immersion in water, 



* Here among other things might he reckoned the order of immersion, for 

 it is a well-known fact, that of two plates of one and the same metal, on 

 being immersed in a like fluid, that dipped in last is always negative to the 

 one lii-st inserted. I have found this to be perfectly true, but have likewise 

 observed that on the contemporaneous immersion of two zinc plates in water 

 slightly acidulated with sulphuric acid, several reversions in the direction of 

 the current are produced ; for instance, in thefirstmomenta westerly deflection 

 of 10°, followed by an easterly of 70°, which was soon succeeded by a perma- 

 nent easterly deflection of 20°, that gradually sunk down to 0°, and passed into 

 a westerly deflection of 38° ; sometimes a couple more reversions occurred. 

 After several contemporaneous takings out and immersions only the westerly 

 deflection was evident. A mere knocking one of the plates against the 

 bottom of the vessel, which produced an elevation of about -V line, rendered this 

 plate negative, or, causing Av'ith respect to the deflection, an increase or diminu- 

 tion in this deflection, although but transitory. The plates employed for this 

 purpose were recently scoured, and at the termination of the experiments, 

 which lasted nearly an houi", they had lost from the weakness of the acid little 

 or nothing of their brightness. Both became covered with bubbles of hydro- 



