In 1809 I presented to the Society a short account of some experiments performed with a voltaic battery of unusually large plates, which has been honoured by publication in the Philosophical Transactions for that year. Since that period I have constructed another of still larger dimensions, the effects of which form the subject of the present communication. The copper and zinc plates of this apparatus are connected together, in the usual order, by leaden straps; they are 6 feet long, by 2 feet 8 inches broad, each plate presenting 32 square feet of surface. All the plates are attached to a strong wooden frame suspended by ropes and pullies, which being balanced by counterpoises, is easily lowered and elevated, so as to immerse the plates in the acid, or raise them out of it, at pleasure. The first trials of the power of this instrument were made in July 1813, in the presence of several philosophical friends, but the effects then fell very short of my expectations, arising, as I afterwards found, from a defect in the construction, which has been since remedied, and another copper plate added to each member of the series, so that every cell now contains one zinc and two copper plates, and each surface of zinc is opposed to a surface of copper. This was done at the suggestion of Dr. Wollaston, and has very considerably increased the power of the battery. From some comparative experiments, which I made with a small apparatus, the increase in quantity of electricity, thus effected, is at least one half. The cells of the battery are 21 in number, and their united capacities amount to 945 gallons. To each pole of the battery a leaden pipe, about 3/4ths of an inch in diameter, is attached by solder, and the opposite end of each pipe immersed in a basin of mercury, (a separate basin for each pipe), by means of which the circuit is compleated, and a perfect contact ensured. The first experiments I shall mention were made on the comparative facility with which different metals are ignited when placed in the electrical circuit. For this purpose, in each experiment, two wires of dissimilar metals were taken, of equal diameter and length; one end of each was in contact with one of the basins of mercury communicating with the poles of the battery, and the other end bent to an angle, and the wires connected continuously by hooking them together. The length of each wire was 8 inches, and the diameter 1/30th of an inch. The battery was moderately excited by a charge of 1 part acid diluted with 40 parts of water.
A SMALL APPARATUS FOR EXTRACTING URINARY ANDROGENS