VOLTAIC KLKCTKinTV. 



129 



VOLT A I < ELECTRICITY. II. 

 QUANTITY A -ilTY DIFFERENT 1OUMS OF BATTERY 



-CKUIKHIJANK'B WOLLA*T<JN' MUNCU'H 

 SMEE'S BICHROMATE PBBSULPHATEDANIEU/B. 



IT will be well, before proceeding further, to explain the main 

 ice between Friotional and Voltaic Electricity. In the 

 :,.:-!ii.-r thi) effect* are produced by a Tory small 



it it is in a state of great tendon, that is, it can 

 frequently penetrate obstruc- 

 tions, and therefore is not 

 confined or insulated. 

 It also exhibits the pheno- 

 mena of attraction and repul- 

 i-ry clearly : if, however, 

 we cause a current of it, or 

 a succession of sparks to pass 

 through water, we shall soon 

 see, by the minute amount 

 uln.-h will be decomposed, 

 ho quantity of fluid is 

 very small. With Voltaic 

 <-ity, on the other hand, 

 in a very largo (]> 

 of the fluid, but it is pos- 

 sessed of but little intensity : 

 it may, therefore, 

 easily be conducted 

 along wires without 

 any great care being 

 required in their in- 

 sulation. Its effects, 

 too, are constant, 

 and instead of ap- 

 pearing in a series of 

 interrupted sparks, 

 it flows in a con- 

 tinuous stream. 



As an illustration 

 of the small quan- 

 tity of electricity 

 generated by fric- 

 tion as compared 

 with that evolved 

 by chemical action, 

 we may give a cal- 

 culation made by 

 the late Professor 

 Faraday. He found 

 that a wire of platinum and 

 one of zinc, each about ^ of 

 an inch in thickness, and im- 

 mersed to a depth of nearly J of 

 an inch in a solution composed 

 of one drop of sulphuric acid to 

 four ounces of water, would pro- 

 duce in three seconds as much 

 electricity as would be obtained 

 from thirty turns of a 50-inch 

 plate electrical machine. 



In a battery, the quantity of 

 electricity obtained depends upon 

 the amount of zinc consumed in 

 the cell, and therefore upon tho 

 area of the single plates. Inten- 

 sity, on the contrary, depends 

 on the number of pairs used. 

 Hence, as we shall see, batteries 



are often fitted so as to be connected in different ways accord- 

 ing as quantity or intensity is required. 



In obtaining electricity in tho mode mentioned in our last 

 lesson, we employed plates of copper and zinc, and this is the 

 combination most frequently used for ordinary telegraphic pur- 

 poses, being cheap and easy to manage. Any two metals, 

 however, may be used, and will produce a current, tho strength 

 of which depends upon tho metals employed. We can, there- 

 fore, construct a large number of different combinations ; not 

 many, however, will bo found sufficient]} effective to pay the 



118 .* 



oo*t of the metal OMd. We may take it M a general rule that 

 one of the metal* nhould be acted on by the eolation M little as 

 possible, the other M much a* possible; and the greater the 

 difference between them in this reepeot, the greater will be the 

 power of tho combination. We may even employ two plate* of the 

 MM metal, if their surfaces be in different conditions one, for 

 instance, being mootb, and the other rough, lit thin caee, 

 however, tho current would be very weak, an moat of the elec- 

 tricity of each would be employed in nentralwing that of the 



other, and only the exoem 

 power of one above the other 

 would be rendered available. 

 Any dingle combination of 

 thin kind in called a pair or 

 an element: when, therefor*, 

 we Hpcak of a battery of 30 

 pairs or element*, we mean 

 that 30 of these combination 

 are placed end to end, the + 

 pole of the one being con- 

 nected with the pole of the 

 next, and so on. 



By means of a series of 

 experiments all metals have 

 been divided into electro-posi- 

 tive and electro-negative. The 

 table given below 

 shows the order in 

 which they are 

 placed ; those at 

 the top of the list 

 are the most easily 

 acted upon, and 

 therefore the moat 

 strongly electro 

 positive. Each 

 metal is therefore 

 + to all those which 

 are below it in the 

 list, and to alf 

 those above it. 

 Thus copper, for 

 instance, is nega- 

 tive if employed 

 together with 

 zinc, but positive 

 when platinum ie 

 the other metal of 

 the pair. 



Tin. 



Bismuth. 



Copper. 



Mercur/_ 



Silver. 



Platinum*. 



Gold. 



Antimony. 



Carbon. 



The exact order in the above 

 list is not always perfectly accu- 

 rate, as it varies a little with 

 the exciting liquid used, ai:d 

 also with the purity or other- 

 wise of the plates of metal ; it 

 will, however, afford a good 

 general idea of their action. 

 The further apart any two sub- 

 stances are in this list, the 



greater will be the power produced by them ; thus, tho most 

 powerful combination would be potassium and carbon, the 

 former of which has such a strong affinity for oxygen, that it 

 immediately decomposes water and inflames its hydrogen, while 

 the latter is quite unchangeable. 



The employment of these substances is prevented by the cost 

 of the former, and by the fact that its action is so powerful that 

 it is almost immediately converted into caustic soda and dis- 

 solved in the water. The experiment may, however, be tried 

 by making it into an amalgam with some other metal. 



