Estimation of Voltaic Energy by Equivalents. 117 
square, was compared, as to the ignition of a platina wire, the 
discharge between points of charcoal, the shock on the human 
frame, Xc., 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. Inall these effects the former appeared quite equal 
to the latter. On comparing a second trough of the new con- 
struction, 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 sur- 
pass 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 con- 
struction; and this was a necessary consequence of the smaller 
quantity of acid used to excite it, which in the case of the forty 
pairs new construction was only one seventh part of that used 
for the forty pairs in the porcelain troughs. ‘To compare, 
thérefore, both forms of the voltaic trough in their decompos- 
ing 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 
23 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 analysed, by being precipitated and boiled with ex- 
cess 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 com- 
parison, 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 equi- 
valent number of water as 9, and of zinc as 32°5, and have 
considered 100 cubic inches of the mixed oxygen and hydro- 
gen, 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,—sul- 
phuric, nitric, and muriatic. The sulphuric acid was strong 
oil of vitriol ; one cubical inch of it was equivalent to 486 grains 
of marble. The nitric acid was very nearly pure; one cubical 
inch dissolved 150 grains of marble. The muriatic acid was 
