ESTIMATION OF VOLTAIC ENERGY BY EQUIVALENTS OF ACTION AND EFFECT. 265 



between the contiguous surfaces of copper to prevent them from coming in contact. 

 Such was the facility afforded by this arrangement, that a trough of forty pairs of 

 plates could be unpacked in five minutes, and repacked again in half an hour ; and 

 the whole series was not more than fifteen inches in length. 



1125. This trough, of forty pairs of plates three inches square, was compared, as to 

 the ignition of a platina wire, the discharge between points of charcoal, the shock 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 em- 

 ployed 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, contain- 

 ing twenty pairs of four-inch plates, with twenty pairs of four-inch plates in porce- 

 lain 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 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 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 decom- 

 posing 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 analysed, 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 de- 

 composed 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 pneu- 

 matic trough, to result from the decomposition of 12-68 grains of water. 



1127. The acids used in these experiments were three, — sulphuric, nitric, and mu- 

 riatic. The sulphuric acid was strong oil of vitriol ; one cubical inch of it was equi- 

 valent to 486 grains of marble. The nitric acid was very nearly pure ; one cubical 

 inch dissolved 150 grains of marble. The muriatic acid was also nearly pure, and 

 one cubical inch dissolved 108 grains of marble. These were always mixed with 

 water by volumes, the standard of volume being a cubical inch. 



2 M 2 



