144 



BLECTBICITY. 



Lesson VI. 



that some of the liberated electricity he 

 abstracted from the zinc, so as to ea use- 

 its density to be less than 1, we should 

 then find that the loss of the + electri- 

 city from the zinc plate would be imme- 

 diately compensated for by the electro- 

 motor force, while an equal amount of 

 electricity to that of the newly-formed + 

 electricity passing to the zinc pi ite, would 

 pass to the copper plate, and thence to the 

 ground. 



73. T. - Is your voltaic pile now fornu-d? 

 P. No; I have only a pair of plates, 



and voltaic piles may consist of any num- 

 ber of plates from 4 to 500 or more, and 

 I have not yet used the moist cloth, which 

 must now be placed upon the zinc, when 

 it will be found that the liberated + elec- 

 tricity will pass from the zinc to the moist 

 cloth; now the effect of this ac-ion is a 

 loss of electricity in the zinc, which is 

 therefore immediately supplied, so that the 

 density of the + electricity of the zinc 

 and cloth will he equal or 1. NVe will now 

 place a copper plate upon the moist cloth, 

 and we shall find that -f- electricity is dis- 

 tributed over it, and has a density of 1, so 

 that -we now say that the under copper 

 plate in connection with the ground, has a 

 density of 0, while + electricity of a den- 

 sity = 1 is on the zinc plate, the moist 

 cloth, and the upper copper plate. 



74. T. Then it appears, that a voltaic 

 pile consists merely of a series of plates of 

 copper and zinc, with an intermediate sub- 

 stance, moist cloth, and that they are 

 arranged in the following order, copper, 

 zinc, cloth, copper, zinc, cloth, copper, &c. 



P. Exactly so, and the density of the 

 electricity is proportioned to the number 

 of pairs of plates used. For example, if 

 we pile the elements in the order you have 

 mentioned to the number of 100, it will be 

 found that the freed + electricity upon 

 the 100th zinc plate will have a density of 

 100. One end of this pile is called the 

 zinc end, or posi'ive pole, and the other 

 the copper end, or negative pole. 



75. T. What would he the effect of 

 insulating the negative pole, and connect- 

 ing the positive one with the ground? 



P. The density of the freed electricity 

 of the zinc end would be 0, and the 

 electricity would be distributed over the 

 whole pile, its density increasing towards 

 the copper end. 



76. T. If thf.se two polos are con- 

 nected, what would be the effect ? 



P. A constant reunion of the electri- 

 cities developed in the pile, but if they 

 are separat.-d a little, we shall observe an 

 uninterrupted current of sparks pass from 

 oue to the other. 



77. T. What do you mean by a gal- 

 vanic circuit ? 



P. All apparatus serving to produce a 

 continual electric current are called gal- 

 vanic circuits, and are generally con- 

 structed of two metals and one fluid, similar 

 to the voltaic pile, which is not so useful 

 as the trough apparatus. 



78. T. What do you mean by the 

 trough apparatus ? 



P. It consists cf several square plates 

 of copper and zinc soldered together, and 

 placed perpendicularly in a wooden trough 

 lined with a coating of resin. The plates 

 are so arranged that there is an interval 

 between each pair, and this is filled with 

 acidulated water, which acts like the moist 

 cloth of Volta's pile. 



79. T. Am I correct in supposing that 

 there are different forms of the galvanic 

 circuit ? 



P. Yes; there are many. When there 

 is only a pair of conductors immersed in 

 a fluid, it is called a single circuit ; when 

 two or more pairs are immersed, it is called 

 a c mpound circuit ; and they are also 

 called voltaic batteries. 



80. T. Is it possible to have a power- 

 ful battery in a small compass? 



P. Yes; I ha\e one 

 here (/ty. 22). It is called 

 a Smee's battery, and con- 

 sists of two plates of amal- 

 gamated zinc (z z), with 

 a plate of platinized si.- 

 ver (s) between them ; 

 these plates, you observe, 

 are confined to a piece 

 of wood (\v) by u bind- 

 ing screw (r/), and the 

 whole immersed inaves- 

 Fig. 22. se j containing dilute sul- 



phuric acid (A).* By means of this bat- 

 tery we obtain immense power without 

 much trouble, and ensure a pretty steady 

 action. Here is another battery (Fig. 23). 

 which is called Daniell's constant bat r cry 



* On- part of .-.:'! to seven of w,-te 



