GALLULMIC ACID. 



GALVANIC BATTKRY. 



2 



the committee of the Hotua of Common*, in 1 758, found to 

 contain 231 ft cubic iuchea. The account of the experiment in 1688 

 was pioservfd, and ia oitod by the committee. 



Tli ale gallon wa* measured in 1700 or thereabout*, and found to 

 contain 282 cubic inches. Ward imagine! that thin gallon WM meant 

 to bear the Mm* relation to a pound avoirdupois which the wine 

 gallon did to a pound troy ; and 231 ia to 282, very nearly a* 5760 to 

 7000, the latter being the proportion* of the two pound*. But if the 

 wine gallon were only 224 cubic inches, then the ale gallon should 

 have been 272} ; or, a* we ahall see, the corn gallon much more nearly 

 coincide* with the hypothesis. 



The corn gallon waa thought, in the middle of the last century, to 

 contain exactly 272| cubic inches. Dr. Bernard, on the game autho- 

 rities, states it to hare been determined at 266 cubic inches; and the 

 statute of 1697, which declare* that a round corn-bushel must be 

 8 inches deep and 184 inches wide, had in fact fixed the gallon at 

 268 Ji cubic inches. 



The imperial gallon, as settled by the Act of Geo. IV., is to contain 

 10 Iba. avoirdupois of distilled water, of which it ia declared that 

 252-45S grains fill a cubic inch :. consequently, the imperial gallon con- 

 tains 277'274 cubic inches; being very nearly a mean between the old 

 ale and (previously to 1697) corn gallon. According to the parlia- 

 mentary standards, then, we have 



Old wine gallon, 231 cubic inches. 

 Old com gallon, 268-6 cubic inches. 

 New imperial gallon, 277'274 cubic inches. 

 Old ale gallon, 282 cubic inches. 



GALLULMIC ACID. [GAJJJO Aero.] 



GALVANIC BATTERY. An apparatus for generating current 

 electricity. The simplest combination which can be formed for this 

 purpose, is that of a plate of zinc and a plate of copper placed, 

 generally, in vertical positions and parallel to one another in a vessel 

 containing a diluted acid, the upper edges of the metals being con- 

 nected by a copper wire. In this state a current of positive electricity 

 passes from the zinc, through the acid, to the copper, and from the 

 latter, along the wire to the zinc : at the same time a current of 

 negative electricity passes from the zinc, along the wire, to the copper, 

 and from thence, through the acid, to the zinc. It is evident that the 

 quantity of fluid furnished by a combination of this kind will be 

 proportional to the superficies on which the acid can act; and on 

 apparatus designated a battery, which may be said to consist of two 

 plates only, one of zinc and the other of copper, was executed many 

 years ago for the London Institution. Each plate was 50 feet long and 

 2 feet wide, and the two were coiled together upon a cylinder of wood, 

 so as to leave everywhere an interval between the two metals : in that 

 interval rope-bands of horse-hair were passed round with the coils so 

 as to keep the metals asunder. The dilute acid was contained in a 

 cylindrical vessel ; and when the battery had to be used, the coils of 

 metal were lowered by machinery into the vessel. 



One of the earliest forms of apparatus was the pile of Volta, in 

 which were combined together a considerable number of small plates 

 of zinc and copper, alternately, with the acid 

 between them. Under GALVANISM ore expla- 

 nations of the electrical action that takes 

 place, and we here merely describe the con- 

 struction of the pile. A circular plate of zinc, 

 i, usually about 14 inch diameter and ,',, inch 

 thick, is laid upon and generally soldered to a 

 thin plate of copper e, of equal diameter; and 

 any convenient number of these are placed 

 above one another, with the copper side under- 

 most in all : between every two compound 

 plates is a circular piece of paper />, or cloth 

 moistened with diluted sulphuric acid; and 

 the whole column or pile is mode to preserve 



i I a vertical position by being formed within 



throe pillars of glass or baked wood, which ore 



connected together by having their extremities inserted in boards, 

 of which the lower one serves as a base for the column. The 

 paper or cloth should be rather less in diameter than the plates of 

 metal ; and no moisture should be allowed to escape over the odircs of 

 the plates. 



In thi* state the lowest plate of zinc attracts the positive electricity 

 from the copper below it, and this continually receives a supply from 

 thaearth through the table, or the base of the pile ; the quantity thus 

 attracted is conveyed to the copper plate immediately above, through 

 the moistened cloth, the latter serving a* a conductor : again, the zinc 

 i the Moond plate attract* electricity from the copper below it, and, 

 at the name time, receives that which is transmitted to the latter from 

 the zinc in tho l.iwert plate. Thus the quantity of positive electricity 

 "> . z c of the second plate becomes nearly twice as great as that 

 which is in the lowest plate ; and the process continuing, the quantity 

 in the nnc of each plate above may be conceived to be such a multiple 

 >f that which is in the lowest plate as is expressed by the number of 

 the compound plate from the bottom of the pile. There is conte- ] 

 n* itly obtained a current of positive electricity passing upward* from ' 

 the tine, through the acid, to the copper; and if a copper wire be ' 



nude to pan frnm the top of the uppermost zinc plate to the copper 

 in the lowest plate, the same current will return downwards, so that a 

 circulation of the fluid will continue till the energy of the pile is ex- 

 hausted. At the same time there is a current of negative ele< 

 pasting down the pile from the copper, through the acid, to the zinc, 

 and returning upwards along the wire. 



If a second pile be formed, the plates in it may be placed in a reverse 

 order, the copper side above and the zinc side below : if a third pile be 

 formed, the order may be the same as in the first pile ; if a fourth, the 

 same as in the second; and so on : then, in uniting them together, a 

 metal wire passe* from the copper at the bottom of the first pile to 

 the zinc at the bottom of the second ; another wire passes from the 

 copper at the top of the second to the zinc at the top of the third, 

 and so on. 



When a wire connects the opposite ends of one pile, or of a system 

 of piles, the circuit is said to be complete : it is said to be broke* if 

 there are two separate wires, one proceeding from the copper at bottom, 

 and the other from the zinc at the top. If an animal body were in 

 connection with the farther extremities of the wires it would complete 

 the circuit, and experience shocks. 



The opposite extremities of the pile, or of the wires which are in 

 contact with them, are called thepola of the battery. As tho current 

 of positive electricity seems to issue from the zinc at the top of the 

 pile, that extremity is called the positive pole of the battery ; at the 

 same tune the negative electricity seems to issue from the copper at 

 the bottom, and therefore the terminating copper plate is called the 

 negative pole. These designations are reversed when a single pair of 

 plates separated by an acid is mentioned. In that case, since the posi- 

 tive electricity passes from the zinc plate, through the acid, to the 

 copper-plate, and the wire passes through the air from the edge of 

 the copper to that of the zinc plate ; it is evident that the positive 

 electricity will flow from the copper, and therefore the copper is the 

 positive pole of the combination ; the negative electricity flowing at 

 the same time along the wire, from the zinc, the latter is the negative 

 pole. The terms ptmtirt and negative poles, as applied to the extremi- 

 ties of the battery, have been objected to on the ground that before 

 connecting the two terminal wires no electricity is evolved, and when 

 the connection is formed the electricity moves in a circuit, no portion 

 of which is apparently more positive or more negative than another 

 portion. Hence Faraday proposed, instead of pole, the word electrode, 

 which signifies a tray : for the negative pole cathode, signifying the 

 detcrndimj way or doumicardt ; and for the positive pole anode, which 

 signifies attending tray or upvxtrdt. In forming these terms he sup- 

 posed the battery to be placed on the ground with its copper or + end 

 to the east, and tho wire connecting the ends of the battery to be bent , 

 into an arc, similar to the course of the sun ; in such case the electric 

 current would flow up from the east end of the battery, and descend 

 into it at the west end. The fluid decomposed by a current passing 

 through it was termed an electrolite: the elements liberated by the 

 decomposition were termed ions ; those which appeared at the cathode 

 were named callous, and those set free at the anode aniont ; thus in 

 the decomposition of sulphate of copper the metal is the cation, and 

 the acid the anion. Daniell employed the word platinadc for the 

 negative, and zincode for the positive pole ; while Graham introduced 

 the terms zincout and chluroui poles, to represent tho-f-and . Much 

 of this nomenclature appears to us to be as uncouth as it is unneces- 

 sary : it was introduced at a time when the introduction of the constant 

 battery by Daniell, and the splendid discoveries by Faraday, had some- 

 what unsettled the scientific mind on the subject of voltaic electricity. 

 The new terms, with a few exceptions, have scarcely obtained a footing; 

 which is not surprising, seeing that the old expression* potitire and 

 negative poles, and electro-potitite, and electro*tgo.tire bodiei, are far 

 more simple and quite ai accurate as the terms by which it is proposed 

 to supersede them. 



As the arrangement of the pile was Inconvenient for experimental 

 purposes, and, moreover, did not give much power, and the power that 

 it did give was soon exhausted, on arrangement was introduced called 

 the troui/h battery, of which there were many forms. Tho first con- 

 sisted of the pile, with tho plates on edge, cemented into grooves made 

 in three sides of a wooden trough, spaces being left between every two 

 compound plates for pouring in dilute acid, which took the place of 

 the paper or cloth. In another form, the trough was made of glazed 

 earthenware, by nine or more parallel partitions of tho same material, 

 which permitted no communication between one cell and another. As 

 many pairs of plates, zinc and copper, of equal superficies, as there 

 were partitions, were provided; the two plates of each pair 

 soldered or fastened together at their upper extremities, so that. Hi. y 

 might be parallel to one another and all were united together by a 

 rod of wood, no that they could at once be placed into 

 from tho cells. The bridges or connections between tho zinc and 

 copper plates stood directly over the partitions, so that there was a 

 copper and a zinc plate in each separate cell, except at one extremity 

 of each trough, in whirli, till two troughs were connected together, the 

 cell had only a zinc plate. When one trough was to be connected with 

 another, in order to increase the battery, a slip of copper, as at a, 

 soldered at the top of a zinc plate, was bent an. I ma-lr t<> enter the 

 cell B, containing only a zinc plate at one end of tho preceding trough. 

 In order to form the complete circuit, one extremity of a wire was 



