It is to the ingenious author of the above experiments, that we are indebted for the invention of the galvanic trough, a disco very which very soon superseded the use of the pile, as being more manageable, and attended with less trouble to the operator. It consists of a wooden box or trough, the depth and breadth of which corresponds with the size of the plates. It is of such a length, in general, as to contain fifty plates, allowing a space of about three-eights of an inch between each pair of plates. The spaces between the plates are formed by grooves, which are to receive the plates. The plates are first soldered together in pairs, one of copper or silver, and one of zinc. The trough being lined with a cement, formed of bees'-wax and resin, the plates, which are previously warmed, are pressed into the grooves, in such order, that the zinc - side of each compound-plate may face ' one way, and the copper or silver the other.
It will be easily perceived, that there is the strictest analogy between the trough and the pile, in point of arrangement. See fig. 1.
The pair of plates of zinc and silver, which, in the pile, are simply laid upon each other, are, in the trough, soldered together, and cemented into the grooves; and the cavity or cells formed by the spaces between each pair of plates, in the trough, being filled with a solution of salt or other appropriate liquid, stands in the stead of the pieces of moistened cloth, between the plates of the pile.
Several powerful troughs were soon after constructed, the effects of which were strikingly evinced, in producing - other phenomena, not as yet observed. Very small wires and foils of metal, being exposed in their circuit, were deflagrated with great brilliancy.
A number of galvanic experiments were made by Dr Henry, of Manchester, in which he succeeded in decomposing the sulphuric and the nitric acids, and am monia.
Mr. Davy, professor of chemistry at the Royal Institution, made a number of ex periments, the most particular of which were those, in which he ascertained, that the dissimilarity of metals was not abso lutely essential to the galvanic process. He succeeded, first, in exciting this energy by means of one metal, the two sides of which were separated from each other. An oxydating liquid, such as an acid, was placed on one side of the plate, and a li quid, having a contrary effect, on the other. He afterwards produced an effect, though more faintly, by treating plates of charcoal in a similar way. Hence it would appear, from these results, that the dissi milarity of the metals was only necessary to the furnishing two surfaces of different degrees of oxydability.
Hitherto it was not generally admitted, that the fluids of galvanism and electri city were identical. Dr. Wollaston made a number of experiments, which seem to have completely settled this point. He sncceeded in decomposing water, by means of a currentfrom the common elec. tric machine. This effect, which had been performed with so much facility with the galvanic apparatus, was previ. ously not known to be able to be produc ed by common electricity, and had hi. therto appeared the most striking differ ence between the two principles.
This ingenious experimentalist made a number of other experiments, tending to throw much light on the means of ex citing and appreciating galvanic pheno mena. He immersed each extremity of a piece of zinc and silver in dilute muriatic or sulphuric acid. The zinc, as would be expected, immediately caused the disen gagement of hydrogen gas, while no ap pearance took place upon the silver. As soon, however, as the two metals were made to touch each other at the opposite extremities, bubbles of hydrogen were copiously given out by the silver wire, Any other metal, capable of being acted upon by the acid, being substituted for the zinc, produced with the silver a simi lar effeet. When gold was employed with silver, iron, or copper, in the dilute nitric acid, the same effect was produced; the gold being the same with the silver in the first experiment.
He made similar experiments, using metallic solutions instead of the dilute acid. Instead, however, of silver or gold giving out hydrogen gas, on the contact being made, the metal in solution became reduced, Thus, when iron and silver v.'ere placed in a solution of copper, the iron immediately began to reduce the copper in solution, while the silver had not the slightest action. Upon bringing the two metals in contact, however, the silver be came coated with copper. Dr. Wallaston attributes the curious phenomon, above described, to a change of states in the elec tricity of the metals ; and in order to con firm this idea, he attempted the s .me by means of common electricity, in which he succeeded to his utmost satisfaction. He supposes, that the chemical affinities are so altered by the presence or absence of electricity, as to induce the anomalous appearances which took place in the above experiments. The silver wire be came coated with copper, and at the same time appeared to have the power of de composing water.