1152.  Again, ten pairs of my four-inch plates (1129.) lost 6.76 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, (1125.) 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 altogether.  In both these cases, therefore, increase of numbers had not been advantageous 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-electrometer, 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 instance, 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.[A]—­The advantageous use of large or small plates for electrolyzations will evidently depend upon the facility with which the transferable power of electricity can pass.  If in a particular case the most effectual number of plates is known (1151.), then the addition of more zinc would be most advantageously made in increasing the size of the plates, and not their number.  At the same time, large increase in the size of the plates would raise in a small degree the most favourable number.

  [A] Gay-Lussac and Thenard, Recherches Physico-Chimiques, tom, i. p. 20.

1155.  Large and small plates should not be used together in the same battery:  the small ones occasion a loss of the power of the large ones, unless they be excited by an acid proportionably more powerful; for with a certain acid they cannot transmit the same portion of electricity in a given time which the same acid can evolve by action on the larger plates.

1156. Simultaneous decompositions.—­When the number of plates in a battery much surpasses the most favourable proportion (1151—­1153.), two or more decompositions may be effected simultaneously with advantage.  Thus my forty pairs of plates (1124.) produced in one volta-electrometer 22.8 cubic inches of gas.  Being recharged exactly in the same manner, they produced in each of two volta-electrometers 21 cubical inches.  In the first experiment the whole consumption of zinc was 88.4 equivalents, and in the second only 48.28 equivalents, for the whole of the water decomposed in both volta-electrometers.