Voltaic Batteries f S^c. 69 



to influence the action of such an arrangement. The conse- 

 quences of this accumulation become strikingly obvious after 

 a plate has been for some hours in use, and without having 

 had its surface cleansed in the interval. 



51. XI. The particular position of the zinc plate whilst in 

 action is needed as equally to be attended to as the position of 

 the copper-plate {II1.)j though the necessity for this has a very 

 different origin in the two cases. A zinc plate whose surfaces 

 are placed in an horizontal plane will have the dissolved sul- 

 phate of zinc resting upon its upper side, and hence inter- 

 posing a stratum of comparatively inactive matter in the place 

 of the existing acid. But when the plate is used in a vertical 

 position, the dissolved sulphate continually subsides, by its 

 superior gravity, from the surface of the plate; thus occa- 

 sioning a perpetually renewed contact to take place between it 

 and the fresh exciting acid. This effect may be rendered vi- 

 sible when a glass vessel, holding an arrangement so suspended, 

 is interposed between the eye and a strong light, when the 

 varying refractions caused by the commingling of the two 

 fluids of different densities, viz. the dissolved sulphate and the 

 acid mixture, will show that a stream of the dissolved salt falls 

 continuously from the bottom edge of the plate, and is finally 

 diffused through the mass of surrounding liquid. 



52. XII. But the continually accelerating action occurring 

 upon the zinc during immersion is the cause of a more fre- 

 quent and variable kind of interference in these experiments 

 than almost any other. A zinc plate whose surface is per- 

 fectly smooth and truly amalgamated (such as are invariably 

 employed in the subsequent experiments), will give a greater 

 amount of action during a second time of immersion than 

 during the first, as appears by the following table : 



No. 2. 



Equal times of immersionlj^^^ 2nd. 3rd. 4th. 5th. 6th. 



or 10 mmutes each . .j 

 Measures of gas in oOths^ 



of a cubic inch yielded V 34-. 36. 38. 42. 50. 59. 



in each time ... .J 



"Whatever may be the strength of the acid used, or, in other 

 words, whatever may be the total length of time needed to 

 produce the same measure of gas, yet, when the plate has been 

 affected to the same extent, whether that may have taken place 

 in a longer or a shorter time, the difference between the rates 

 of action in the first and last portions of the total time will 

 be the same as exhibited by this table. 



53. XIII. Again, the acid solution becomes weakened by 



