1129.  Similar experiments were made with two voltaic batteries, one containing twenty pairs of four-inch plates, arranged as I have described (1124.), and the other twenty pairs of four-inch plates in porcelain troughs.  The average of five experiments with the former was a consumption of 3.7 equivalents of zinc from each plate, or 74 from the whole:  the average of three experiments with the latter was 5.5 equivalents from each plate, or 110 from the whole:  to obtain this conclusion two experiments were struck out, which were much against the porcelain troughs, and in which some unknown deteriorating influence was supposed to be accidentally active.  In all the experiments, care was taken not to compare new and old plates together, as that would have introduced serious errors into the conclusions (1146.).

1130.  When ten pairs of the new arrangement were used, the consumption of zinc at each plate was 6.76 equivalents, or 67.6 for the whole.  With ten pairs of the common construction, in a porcelain trough, the zinc oxidized was, upon an average, 15.5 equivalents each plate, or 155 for the entire trough.

1131.  No doubt, therefore, can remain of the equality or even the great superiority of this form of voltaic battery over the best previously in use, namely, that with double coppers, in which the cells are insulated.  The insulation of the coppers may therefore be dispensed with; and it is that circumstance which principally permits of such other alterations in the construction of the trough as gives it its practical advantages.

1132.  The advantages of this form of trough are very numerous and great. i.  It is exceedingly compact, for 100 pairs of plates need not occupy a trough of more than three feet in length, ii.  By Dr. Hare’s plan of making the trough turn upon copper pivots which rest upon copper bearings, the latter afford fixed terminations; and these I have found it very convenient to connect with two cups of mercury, fastened in the front of the stand of the instrument.  These fixed terminations give the great advantage of arranging an apparatus to be used in connexion with the battery before the latter is put into action, iii.  The trough is put into readiness for use in an instant, a single jug of dilute acid being sufficient for the charge of 100 pairs of four-inch plates, iv.  On making the trough pass through a quarter of a revolution, it becomes active, and the great advantage is obtained of procuring for the experiment the effect of the first contact of the zinc and acid, which is twice or sometimes even thrice that which the battery can produce a minute or two after (1036. 1150.). v.  When the experiment is completed, the acid can be at once poured from between the plates, so that the battery is never left to waste during an unconnected state of its extremities; the acid is not unnecessarily exhausted; the zinc is not uselessly consumed; and, besides avoiding these evils, the charge is mixed