GALVANISM. 



very jiowetful in producing light and heat. In a 

 battery formed by Mr Children, on Dr Wollaston's 

 plan, each plate was six feet by two feet eight inches, 

 presenting a surface of about thirty-two square feet. 

 The same principle was applied, a few years since, by 

 Mr Hart, of Glasgow, in the construction of a battery 

 without a trough. He formed his battery of copper 

 cells, each of such capacity within, as to contain a 

 zinc plate, together with so much of the acidulated 

 fluid as would allow the copper to be immersed, 

 nearly to the top. The zinc plates are suspended in 

 the copper cells by means of brass wires at their tops, 

 which are fixed in a cross bar of baked wood; and 

 each copper cell is made to communicate with the 

 B'UIC plate in the next cell, by means of a thin slip of 

 copper, each cell communicating only with one zinc 

 plate. The acid solution is introduced into the cells 

 by immersing them in a leaden trough, containing the 

 fluid; when they are taken out, the battery is in ac- 

 tion. Another ingenious modification of the battery 

 has been contrived by Dr Hare of Philadelphia. It 

 consists of concentric coils of copper and zinc, so sus- 

 pended by beams and levers as to be made to de- 

 scend, at pleasure, instantaneously into the exciting 

 fluid contained in glass jars or wooden troughs, 

 without partitions. Each coil is formed from a zinc 

 sheet of nine inches by six, and one of copper four- 

 teen by six, more of the copper being required, as 

 this metal is made to commence within the zinc, and 

 completely to surround it without. The sheets are 

 so coiled as to leave between them interstices of a 

 quarter of an inch. In the original apparatus, they 

 were arranged in two rows, forty coils in each : on 

 their immersion in the appropriate fluid, the imme- 

 diate evolution of heat and light was found to be 

 most intense, far exceeding that of voltaic piles or 

 troughs of an equal number of series and extent of 

 surface ; and on account of its superior power of 

 causing the combustion of metallic wires and leaves, 

 the instrument was named, by its inventor, the gal- 

 vanic defiagrator. The size of the plates composing 

 the galvanic series has been varied from one or two 

 inches square to that of a great number of feet. The 

 battery of Mr Children consisted of twenty pairs of 

 copper and zinc plates, each plate being six feet long 

 by two feet eight inches broad. Each pair was con- 

 nected by leaden straps at the top, and had a separ- 

 ate wooden cell. These cells were capable of con- 

 taining 945 gallons of liquid. The plates were 

 suspended from a wooden beam, by means of which 

 they could at once be lowered into the cells, and 

 again raised, at pleasure. Doctor Hare constructed 

 an apparatus consisting of twenty sheets of copper 

 and the same number of zinc, each twenty inches 

 square, and so arranged as to be equivalent to a 

 battery of two galvanic pairs, excepting that there is 

 no insulation, all the plates being plunged into one 

 vessel. This instrument, from its evolving caloric 

 with scarcely any electricity, was called by Doctor 

 Hare the calorimotor. Messrs Wetherell and Peale, 

 of Philadelphia, experimented with still larger pairs 

 in the form of concentric coils ; one pair containing 

 nearly 70 square feet of each metal, and another 

 nearly 100. In the London institution, Chere is an 

 efficient battery, the energy of which is derived from 

 a simple galvanic circle. The instrument consists oi 

 two plates, the one of zinc, and the other of copper, 

 coiled round one cylinder of wood, and kept asunder 

 by the interposition of thick cords of horse hair, 

 placed at intervals between the plates. Each plate 

 is two feet broad and sixty long, and when it is re- 

 quired to be put in action, it is only necessary to put 

 the coil endwise into a vessel containing the acid so- 

 lution. 



Different liquids are employed to fill the cavities of 



he trough ; and it is essential to employ those which 

 ;xert a chemical action upon one of the metals, the 

 effect with pure water being very inconsiderable. In 

 general, the galvanic effect is proportional to the 

 rapidity with which the more oxidable metal is acted 

 upon by the intervening fluid. Thus where the liquid 

 employed is pure water, the electric excitement is 

 very feeble, for the action on the metals is feeble ; 

 still the zinc is, even in this arrangement, observed 

 to be oxidized more rapidly than it would be, were it 

 not in contact with the copper. A saline solution, 

 as of muriate of soda, or muriate of ammonia, is 

 found to cause a more rapid oxydation of the zinc ; 

 and, accordingly, the electric power is greater: and, 

 lastly, an acid fluid, which oxygenates and dissolves 

 the metals much more rapidly, produces the highest 

 activity of which the battery is capable. The fluid 

 generally used is nitric acid, diluted with twenty or 

 thirty times its weight of water. The electric column, 

 originally contrived by M. de Luc, is usually classed 

 with galvanic arrangements. It is formed of discs 

 of Dutch gilt paper and similar discs of laminated 

 zinc. These, in a perfectly dry state, are piled up 

 into two columns, the different metals constantly al- 

 ternating with each other in their position, until they 

 attain the height of eighteen inches, when they are 

 coated over with a glass cylinder. They are then 

 placed at the distance of four or five inches from each 

 other, and between them is suspended, on a pivot, a 

 light steel needle, which is attracted alternately to the 

 one pile and the other, moving between them like a 

 pendulum. This curious instrument, instead of being 

 soon exhausted, like the pile, with humid substances, 

 is found to continue active for several years, and 

 has been applied to the measurement of time, by 

 causing it to give motion to the pendulum of a 

 clock. 



2. Electrical Effects of the Galvanic Battery. 

 Under this head are included all the effects which 

 resemble the usual phenomena produced by the elec- 

 trical machine. Galvanism, even when excited by a 

 single galvanic circle, such as a piece of zinc, a simi- 

 lar one of copper, and a piece of cloth moistened 

 with a solution of muriate of ammonia, distinctly 

 affects the gold haf of the condensing electrometer. 

 If the zinc end be uppermost, and be connected 

 directly with the instrument, the electricity indicated 

 is positive. If the pin of the electrometer touch the 

 copper, the electricity is negative. When wires 

 connected with the opposite poles, or sides, of an 

 active galvanic trough, are brought near each other, 

 a spark is seen to pass between them, accompanied 

 with a slight snap or report, and, on establishing a 

 communication by means of the hands, previously 

 moistened, a distinct shock is perceived, similar to 

 that which is produced by the discharge of a Leyden 

 jar. Both influences, also, are propagated through 

 a number of persons without any perceptible interval 

 of time. On connecting the ends of a sufficiently 

 powerful battery, by means of fine metallic wires, or 

 slender pieces of freshly prepared charcoal, these 

 conductors become intensely heated, and a vivid 

 white light appears at the points of the charcoal ; 

 and as this phenomenon takes place equally in an 

 atmosphere void of oxygen gas, or even under the 

 surface of water, it manifestly cannot be ascribed to 

 combustion. If the communication be established by 

 metallic leaves, the metals burn with vivid scintilla- 

 tions ; and, if the galvanic fluid, in its circuit, be 

 made to pass through gunpowder, phosphorus, and a 

 mixture of hydrogen and oxygen gases, they are in- 

 flamed. These observations induced the belief, that 

 the agent or power excited by the voltaic apparatus 

 is identical with that which is called into activity by 

 the electrical machine ; for not only may all the 



