1141.  Again, when a charge consisting of 200 water, 4-1/2 oil of vitriol, and 4 nitric acid was used, each zinc plate lost 2.16 equivalents; when the charge with the same battery was 200 water, 9 oil of vitriol, and 8 nitric acid, each zinc plate lost 2.26 equivalents.

1142.  I need hardly say that no copper is dissolved during the regular action of the voltaic trough.  I have found that much ammonia is formed in the cells when nitric acid, either pure or mixed with sulphuric acid, is used.  It is produced in part as a secondary result at the cathodes (663.) of the different portions of fluid constituting the necessary electrolyte, in the cells.

1143. Uniformity of the charge.—­This is a most important point, as I have already shown experimentally (1042. &c.).  Hence one great advantage of Dr. Hare’s mechanical arrangement of his trough.

1144. Purity of the zinc.—­If pure zinc could be obtained, it would be very advantageous in the construction of the voltaic apparatus (998.).  Most zincs, when put into dilute sulphuric acid, leave more or less of an insoluble matter upon the surface in the form of a crust, which contains various metals, as copper, lead, zinc, iron, cadmium, &c., in the metallic state.  Such particles, by discharging part of the transferable power, render it, as to the whole battery, local; and so diminish the effect.  As an indication connected with the more or less perfect action of the battery, I may mention that no gas ought to rise from the zinc plates.  The more gas which is generated upon these surfaces, the greater is the local action and the less the transferable force.  The investing crust is also inconvenient, by preventing the displacement and renewal of the charge upon the surface of the zinc.  Such zinc as, dissolving in the cleanest manner in a dilute acid, dissolves also the slowest, is the best; zinc which contains much copper should especially be avoided.  I have generally found rolled Liege or Mosselman’s zinc the purest; and to the circumstance of having used such zinc in its construction attribute in part the advantage of the new battery (1134.).

1145. Foulness of the zinc plates.—­After use, the plates of a battery should be cleaned from the metallic powder upon their surfaces, especially if they are employed to obtain the laws of action of the battery itself.  This precaution was always attended to with the porcelain trough batteries in the experiments described (1125, &c.).  If a few foul plates are mingled with many clean ones, they make the action in the different cells irregular, and the transferable power is accordingly diminished, whilst the local and wasted power is increased.  No old charge containing copper should be used to excite a battery.