GALVANIC INSTRUMENTS. 



325 



Zinc and Copper Plates, with Glass 

 Handles. (Fig. 382.) Pair of cir- 

 cular zinc and copper plates, with 

 glass insulating handles, for showing, ___ 



by the aid of a very delicate condens- ^^^^""| 

 ing electroscope, electricity developed 

 by two dissimilar metals that have 

 been in contact and are separated. 

 Price, $2.00. 



- 332. 



* 



Cruikshank's Trough Fi s . 3S3. 



Battery (Figs. 383 and 

 384) consists of plates 

 of zinc and copper, unit- 

 ed by their flat surfaces 

 by soldering, and ce- 

 mented into grooves in 

 the sides of a trough of 

 baked wood, so as to leave sufficient intervals to hold small 

 quantities of fluid, usually about half an inch wide ; they 

 must of course be arranged so that all the zinc surfaces shall 

 be on one side, and all the copper surfaces on the other. 

 The battery is charged by filling the cells with a saline solu- 

 tion, or with dilute acid, and the galvanic circuit completed 

 by bringing the two wires proceeding from the ends of the 

 battery in contact with one another. One of the figures 

 represents a trough having three rows of plates connected 

 together by wires. Troughs of this construction are ex- 

 Fig. 384 



ceedingly liable to get out of order, from the action of the 

 liquid on the wood, which it tends to warp. The plates 

 require to be fixed into the grooves by cement, in order to 

 render them water tight ; but this cement is apt to crack 

 from the warping of the wood and other causes, and the 

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