272 DR. FARADAY'S EXPERLMENTAL RESEARCHES IN ELECTRICITY. 



1150. First immersion of the plates. — The great effect produced at the first im- 

 mersion of the plates, (apart from their being new or used (1146.),) I have attributed 

 elsewhere to the unchanged condition of the acid in contact with the zinc plate 

 (1003. 1037.) : as the acid becomes neutralized, its exciting power is proportionably 

 diminished. Hare's form of trough secures much advantage of this kind, by mingling 

 the liquid, and bringing what may be considered as a fresh surface of acid against 

 the plates every time it is used immediately after a rest. 



1151. Number of plates*. — The most advantageous number of plates in a battery 

 used for chemical decomposition, depends almost entirely upon the resistance to be 

 overcome at the place of action ; but whatever that resistance may be, there is a cer- 

 tain number which is more economical than either a greater or a less. Ten pairs of 

 four-inch plates in a porcelain trough of the ordinary construction, acting in the 

 volta-electrometer (1126.) upon dilute sulphuric acid of spec. grav. 1*314, gave an 

 average consumption of 15*4 equivalents per plate, or 154 equivalents on the whole. 

 Twenty pairs of the same plates, with the same acid, gave only a consumption of 5*5 

 per plate, or 110 equivalents upon the whole. When forty pairs of the same plates 

 were used, the consumption was 3*54 equivalents per plate, or 14 1*6 upon the whole 

 battery. Thus the consumption of zinc arranged as twenty plates was more advan- 

 tageous than if arranged either as ten or as forty. 



1152. Again, ten pairs of my four-inch plates (1129.) lost Q'JQ each, or the whole 

 ten 67 '6 equivalents of zinc, in effecting decomposition ; whilst twenty pairs of the 

 same plates, excited by the same acid, lost 3*7 equivalents each, or on the whole 74 

 equivalents. In other comparative experiments of numbers, ten pairs of the three- 

 inch plates (1 125.) lost 3*725, or 37*25 equivalents upon the whole ; whilst twenty pairs 

 lost 2*53 each, or 50*6 in all ; and forty pairs lost on an average 2*21, or 88*4 alto- 

 gether. In both these cases, therefore, increase of numbers had not been advan- 

 tageous as to the effective production of transferable chemical power from the whole 

 quantity of chemical force active at the surfaces of excitation (1120.). 



1153. But if I had used a weaker acid or a worse conductor in the volta-electro- 

 meter, then the number of plates which would produce the most advantageous effect 

 would have risen ; or if I had used a better conductor than that really employed in 

 the volta-electrometer, I might have reduced the number even to one ; as, for in- 

 stance, when a thick wire is used to complete the circuit (865., &c.). And the cause 

 of these variations is very evident, when it is considered that each successive plate in 

 the voltaic apparatus does not add anything to the quantity of transferable power or 

 electricity which the first plate can put into motion, provided a good conductor be 

 present, but tends only to exalt the intensity of that quantity, so as to make it more 

 able to overcome the obstruction of bad conductors (994. 1158.). 



1154. Large or small plates-^-. — The advantageous use of large or small plates for 

 electrolyzations will evidently depend upon the facility with which the transferable 



* Gat-Ltjssac and Thenard, Recherches Physico-Chimiques, torn. i. p. 29. f Ibid. 



