261 



GALVANIC BATTERY. 



GALVANIC BATTERY. 



262 



made to enter the cell A, for example, which was the positive end, and 

 the other extremity was brought to the opposite end of the trough, or 



U I i -i ii L 

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U L ti L LULU La 

 Z C 2 



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series of troughs, where it was placed in contact with the copper slip, 

 as a : the positive current then flowed along the wire from the ex- 

 tremity first mentioned to the other. 



The above form was contrived by Mr. Children ; but Dr. Wollaston 

 proposed, as an improvement upon it, to have in each cell a zinc plate 

 between two plates of copper ; for thus both surfaces of each zinc plate 

 would become efficient in producing the electric current, and the power 

 of the battery would be increased by one half. The battery at the 

 Royal Institution was of Mr. Children's kind ; it contained 2000 pairs of 

 plates, each 8 inches long and 4 inches deep, and with it Sir Humphry 

 Davy made his principal discoveries. 



The battery invented by Professor Daniell consists of any number 

 of cylindrical vessels of copper, open at the top, about 16 inches high 

 and 3 inches in diameter, and containing a saturated solution of 

 sulphate of copper ; the exterior surface of each may be painted, but 

 the interior, which alone is efficient in producing electricity, is made 

 bright. On, the top of the cylinder is 

 placed a hemisphere a of wood, through 

 which, in the direction of the axis of 

 the cylinder, is a perforation above an 

 inch in diameter; and to its base is 

 attached a short tube b of copper, less in 

 diameter than the cylinder, and carrying 

 near its upper extremity an annular plate 

 c of copper, in which are pierced several 

 small holes. When the wooden cover is 

 placed on the cylinder its base rests on 

 the top of the latter; and the part of 

 the cylinder between the short tube 

 and the annular plate is filled with 

 crystals or pieces of sulphate of copper, 

 which, gradually dissolving, preserve the 

 strength of the solution in the lower part 

 of the cylinder. 



To the interior of the short tube was 

 affixed, in the original arrangement, one 

 end of a piece of ox gullet d, about the 

 same length as the copper cylinder, and 

 having its lower extremity tied so that 

 the whole formed a membranous bag ; this is to contain diluted sul- 

 phuric acid (eight parts water to one of acid). A rod of zinc z, about 

 the same length as the cylinder, an inch in diameter, and terminating at 

 the upper extremity with a brass ball, is passed through the perforation 

 in the wood, down the interior of the membrane, so that its shoulder 

 rests on the top of the wood ; the surface of the zinc being previously 

 covered with an amalgam of mercury. Instead of a membrane, a bag 

 of paper or canvas, or a vessel of porous earthenware, may be more 

 conveniently used. 



If now, a connection, by means of a wire or metallic rod, were made 

 between the ball at the top of the zinc rod and the top of a stem e 

 which rises from one side of the copper cylinder, the zinc will be 

 corroded by the sulphuric acid, and the electric fluid will pass to the 

 copper through the acid, the membrane, and the solution in the 

 cylinder. [GALVANISM.] 



The battery invented by Mr. Grove consists of several porous vessels 

 containing strong nitric acid, and, in each, a rod or plate of platinum ; 

 each of these vessels is placed between two plates of zinc within a 

 trough in which is diluted sulphuric or muriatic acid. The rod of 

 platinum holds the place of the plate of copper in Children's battery, 

 and constitutes the negative pole of each combination ; the zinc plate 

 being the positive pole. By mixing sulphuric acid with the nitric 

 acid in> the porous cells, a more uniform current ia obtained. This 

 battery is expensive, and must be placed under a chimney or a hood to 

 carry off the nitrous fumes. For the sake of economy Bunsen uses, 

 instead of the platinum, cylinders of carbon prepared by heating a 

 mixture of powdered coke and caking coal, or powdered coke moistened 

 with a strong solution of sugar. The carbon answers very well while 

 fresh, but it soon deteriorates by absorbing the nitric acid. Poggen- 

 dorf uses sheet or cast iron, which is not acted on by strong nitric acid. 

 In Srnee's battery the negative or conducting plate is of silver, on 

 which finely divided platinum has been deposited, this roughness of 

 surface facilitating the escape of the hydrogen ; each side of the silver 

 plate is exposed to a plate of amalgamated zinc of the same size, 



which acts as the positive plate, and is excited by dilute sulphuric 

 acid. 



Grove's gas lattery possesses a theoretical, rather than a practical 

 interest. It is stated, under GALVANISM, that the amount of force set 

 in motion in a voltaic arrangement depends on the difference between 

 the affinity of the two metals for the active principle, or radicle of the 

 acid. The liquid which excites the chemical action ia decomposed, its 

 elements are separated, and they either combine with the metallic 

 plate, or accumulate on its surface. By these means the voltaic action 

 is opposed and enfeebled, in consequence of the tendency of the com- 

 ponent parts of the fluid to re-unite; for example/when dilute sulphuric 

 acid is used, it is important to get rid of the hydrogen which adheres 

 to the platinum, and produces a counter-current, which may be made 

 evident by connecting a platinum plate, opposed to a zinc plate with a 

 galvanometer wire, when, on attaching to the other end of the galva- 

 nometer wire another platinum plate, free from hydrogen bubbles, 

 and plunging both into dilute acid, the needle will be powerfully 

 deflected. In the gas battery a plate covered with oxygen, is opposed 

 to a plate covered with hydrogen. A cell of this battery consists of 

 two tubes ; through the upper end of each is soldered a platinum wire 

 attached to a platinum plate extending to the bottom of the tube. 

 The hydrogen tube has twice the capacity of the oxygen, and the tubes 

 are supported in a vessel containing dilute sulphuric acid. At the 

 beginning of the experiment the tubes are filled with the dilute acid, 

 and are charged with gas, by being connected with a voltaic battery. 

 When the tubes are in this way charged, they are separated from the 

 battery, and the mercury cups at the top of the tubes being connected 

 with a galvanometer there is a strong deflection of the needle, and by 

 connecting 8 or 10 cells in such a way that the oxygen of one cell may 

 be connected with the hydrogen of the next cell, sparks between 

 charcoal points and various chemical decompositions may be obtained. 

 The gases gradually diminish in bulk, but the current is maintained so 

 long as they remain uncombined. 



For the formation of a voltaic circuit, it is usually stated that two 

 dissimilar metals, and a fluid acting upon one of them, are required. 

 We have seen in the case of the gas battery a variation from this rule, 

 which may be still farther departed from in various ways. For ex- 

 ample : if a single metal be plunged one end into a liquid capable of 

 acting on it, while the other end is dipped into a different liquid com- 

 municating freely with the first liquid, but having little or no action 

 on the metal, a current will be established. If, for example, we place 

 in the bend of a JJ tube a piece of tow, and in one limb pour in a 

 solution of chloride of copper, and in the other limb one of common 

 salt, and connect the two open ends of the tube by means of a strip of 

 copper dipping therein, crystals of copper will be formed upon the 

 end of the strip immersed in the metallic solution, while the end of 

 the strip immersed in the salt and water will be corroded, and chloride 

 of copper be formed. By using various liquids in the two limbs, 

 Becquerel has obtained many of the metals in beautiful crystalline 

 forms. It has also been shown that similar actions are going on 

 within the earth's crust; for by connecting, by means of wires 

 attached to a galvanometer, the surfaces of two contiguous lodes of 

 ore, the existence of feeble but continuous currents was detected. 



The battery used at first by Professor Wheatstone for his electrical 

 telegraph was formed nearly on the same principle as that of Mr. 

 Daniell. A small outer vessel contained a solution of sulphate of 

 copper, together with the plate of copper which formed the negative 

 pole ; within this, a small porous cell contained diluted sulphuric acid, 

 and at the bottom was an amalgam of zinc and mercury, which con- 

 stituted the positive pole. Various other forms of battery, and also 

 an electro-magnetic apparatus, have been employed for working the 

 telegraph. [TELEGRAPH.] 



A notice of galvanic apparatus would not be complete without 

 referring to Deluc's dry pile, which consists of circular disks of paper, 

 one surface of which is coated with leaf gold or silver, and the other 

 surface with zinc foil. Some thousands of these disks are arranged in 

 a glass tube, with all the zinc surfaces in one direction, and the silvered 

 or gilt surfaces in the other direction. If these disks be pressed 

 together, and a wire attached to each end, the leaves of the gold-leaf 

 electroscope may be made to diverge by touching the cap of the instru- 

 ment with one end of the pile, and connecting the other end with the 

 earth. If the two ends of the pile be made to terminate in metal 

 disks placed about an inch or so from each other, and be well insulated, 

 an insulated slip of gold-leaf suspended midway between them will 

 oscillate backwards and forwards for months, and even years. A dry 

 pile consisting of 20,000 disks gave sparks, and charged a Leyden 

 battery so as to produce shocks. The term dry pile is, however, a 

 misnomer, since the action depends on the moisture contained in paper 

 when exposed to the air : if the paper be artificially dried the pile 

 ceases to act. Zamboni substituted finely-powered peroxide of manga- 

 nese for the gold or silver leaf, with good effect. The pile terminated 

 in metal plates, which compressed the paper disks by means of ligatures 

 of silk, and the pile was insulated by giving it a coating of sulphur. 



In all voltaic actions power is transferred by means of a polar 

 influence propagated through the solid as well as the liquid particles of 

 the circuit. As a consequence of polarisation we get electric tension, 

 the effects of which may be shown by a numerous series of alternations 

 of zinc and copper (Mr. Gassiot's battery consisted of 3520 pairs), each 



