PHYSIOLOGICAL PHYSICS. 



[Chap. II. 



hermetically-sealed cover, through which communica 

 tioh is made by binding screws v v'. Little rubber 



pads keep the plates of zinc and 

 silver from contact, the silver 

 being also surrounded by a 

 tube of muslin, while a band 

 JK fixes them. The liquid is 

 a solution of chloride of sodium. 

 By the action of the cell zinc 

 chloride is formed, and silver is 

 reduced and deposited, in a 

 Fig. 13. Gaifl'e's Element, pulverised state, in the muslin 



bag. The element is made in 



a portable form, the liquid not being able to escape. 

 For recharging, new plates of zinc and silver are neces- 

 sary. [For elements for medical purposes, see page 150.] 



Silver is + pole. 



Suppose the electromotive force of a Darnell's 

 element to be represented by 1, then that of Grove 

 and Bunsen would be nearly 1-8, while that of Smee 

 would be less than *4. 



Battery. Several cells may be united together, 

 as shown in Fig. 14, to form a battery. Here the 

 zinc of one element is 

 connected with the copper 

 of another. There is 

 thus left at one end of 

 the series an unoccupied 

 copper, and at the other 

 end an unoccupied zinc. 

 These are the terminals, 



or poles, of the battery, copper being + and zinc 

 -, and wires are attached to these for conducting 

 the electricity to the desired place. At page 28 the 

 different methods of connecting cells to form a battery 

 are discussed. 



Fig. 14. Battery. 



