ock on the human frame, &c., with forty pairs of
four-inch plates having double coppers, and used in porcelain troughs
divided into insulating cells, the strength of the acid employed to excite
both being the same. In all these effects the former appeared quite equal
to the latter. On comparing a second trough of the new construction,
containing twenty pairs of four-inch plates, with twenty pairs of four-inch
plates in porcelain troughs, excited by acid of the same strength, the new
trough appeared to surpass the old one in producing these effects,
especially in the ignition of wire.

1126. In these experiments the new trough diminished in its energy much
more rapidly than the one on the old construction, and this was a necessary
consequence of the smaller quantity of acid used to excite it, which in the
case of the forty pairs of new construction was only one-seventh part of
that used for the forty pairs in the porcelain troughs. To compare,
therefore, both forms of the voltaic trough in their decomposing powers,
and to obtain accurate data as to their relative values, experiments of the
following kind were made. The troughs were charged with a known quantity of
acid of a known strength; the electric current was passed through a
volta-electrometer (711.) having electrodes 4 inches long and 2.3 inches in
width, so as to oppose as little obstruction as possible to the current;
the gases evolved were collected and measured, and gave the quantity of
water decomposed. Then the whole of the charge used was mixed together, and
a known part of it analyzed, by being precipitated and boiled with excess
of carbonate of soda, and the precipitate well-washed, dried, ignited, and
weighed. In this way the quantity of metal oxidized and dissolved by the
acid was ascertained; and the part removed from each zinc plate, or from
all the plates, could be estimated and compared with the water decomposed
in the volta-electrometer. To bring these to one standard of comparison, I
have reduced the results so as to express the loss at the plates in
equivalents of zinc for the equivalent of water decomposed at the
volta-electrometer: I have taken the equivalent number of water as 9, and
of zinc as 32.5, and have considered 100 cubic inches of the mixed oxygen
and hydrogen, as they were collected over a pneumatic trough, to result
from the decomposition of 12.68 grains of water.

1127. The acids used in these experiments were three,--sulphuric, nit