-3ALVANISM. 



401 



How may bod- 

 ies capable of 

 exciting elec- 

 tro-motire 

 forces be classi- 

 fied? 



773. Different bodies placed in contact manifest differ- 

 ent electro-motive forces, or develop different quantities 

 of electricity. 



Bodies capable of developing electricity by contact may bo 

 arranged in a series in such a manner that any one placed in 

 contact with another holding a lower place in the series, will 

 receive the positive fluid, and the lower one the negative fluid ; 

 and the more remote they stand from each other in the order 

 of the series, the more decidedly will the electricity be developed by their 

 contact 



The most common substances used for exciting galvanic electricity may be 

 arranged in such a series as follows : — zinc, lead, tin, antimony, iron, brass, 

 copper, silver, gold, platinum, black lead or graphite, and charcoal. 



Thus, zinc and lead, when brought in contact, wOl produce electricity, but 

 it will be much less active than that produced by the union of zinc and iron, 

 or the same metal and copper, and the last less active than zinc and platinum 

 or zinc and charcoal. 



774. In the production of galvanic electricity for practical, 

 purposes, it is necessary to have a combination of three dif- 

 ferent conductors, or elements, one of which must be solid 

 and one fluid, whQe the third may be either soHd or fluid. 

 The process usually adopted is to place between two plates 

 of difFerent kinds of metal a liquid capable of exciting some chemical action 

 on one of the plates, while it has no action, or a different action upon tho 

 other. A communication is then formed between the two plates. 



When two metals capable of exciting elec- 

 tricity are so arranged and connected that tbo 

 positive and negative electricities can meet and flow in 

 opposite directions, they are said to form a galvanic cir- 

 cuit, or circle. 



T^ .. . A very simple, and 



Describe a siin- ■' ^ 



pie Galvaaic at the same time an ac- 

 Battery. tive galvanic circuit may 



be formed by an arrangement as repre- 

 sented in Fig. 333. C and Z are thin 

 plates of copper and zinc immersed in a 

 glass vessel containing a very weak so- 

 lution of sulphuric acid and water. 

 MetaUic contact can be made between 

 the plates by wires, X and W, which 

 are soldered to them. If now the wires 

 are connected, as at Y, a galvanic cir- 

 cuit will be formed ; positive electricity 

 passing from tho zinc through the liq- 



Wbat is the 

 practical meth- 

 od of exciting 

 galvanic elec- 

 tricity ? 



What is a Gal- 

 Tanic Circuit f 



Fig. 333. 



