GALVANISM. 



being contained in a given space. The 

 zinc and copper plates are united in 

 pairs, as before, by a slip of metal pass- 

 ing from the one and soldered to the 

 other : each pair being placed so as to 

 enclose a partition between them, and 

 each cell containing a plate of zinc con- 

 nected with the copper plate of the suc- 

 ceeding cell, and a copper plate joined 

 with the zinc plate in the preceding cell. 

 Such an apparatus is called a trough 

 battery, and is represented in Jig. 9. 



Fig. 9. 



The trough, T, may be made of baked 

 mahogany, with partitions of glass : 

 but it is found more convenient to con- 

 struct the whole of one material, and 

 Wedgwood ware answers best for this 

 purpose. Each trough is usually fitted 

 up with ten or twelve cells. The plates, 

 P, adapted to them, are connected to- 

 gether by a slip of baked wood, so as to 

 allow of their bein; let down into the 

 cells, or lifted out, together. A further 

 advantage arises from this construction, 

 that the plates and the fluid being inde- 

 pendent of each other, the former may 

 be readily cleaned or replaced, when 

 worn or injured, without disturbing the 

 fluid : and the latter may, in like man- 

 ner, be removed and changed with the 

 utmost facility. A number of these 

 troughs may be combined with great 

 ease, by connecting together the termi- 

 nal plates of the adjoining troughs, by 

 slips of copper; taking care, as in the 

 case of the pile, ($ 11.) to preserve 

 throughout the whole series the same 

 order of alternation in the plates, by 

 connecting the zinc end of one battery 

 with the copper end of the next. 



The voltaic battery belonging to the 

 Royal Institution, which is of immense 

 power, is constructed on the plan above 

 described, and consists of 200 separate 

 parts, each part composed of ten double 



plates, and each plate containing thirty- 

 two square inches. The whole number 

 of double plates is 2000, and the whole 

 surface 128,000 square inches. 



(17.) A trough battery on another 



construction was invented by Mr. 



Cruickshanks, and is represented in 



fig. 10. Plates of zinc and of copper, 



Fig. 10. 



united by their flat surfaces by solder- 

 ing, are employed to form the partitions 

 themselves, and are fixed into grooves in 

 the sides of a trough of baked wood, 

 which is a bad conductor of electricity, 

 so as to leave sufficient intervals to hold 

 small quantities of fluid. 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 solution, 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. The section, /g-. 11, 

 Fig. 11. 



will tend to elucidate the principles of 

 its action. Troughs of this construc- 

 tion, however, are exceedingly 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 ce- 

 ment is apt to crack from the warping 

 of the wood, and other causes, and the 

 liquid insinuating itself into the fissures, 

 impairs the power of the instrument by 

 destroying the insulation of the cells. 



(18.) The power of a battery is con- 

 siderably increased when both surfaces 

 of each plate of zinc, in contact with the 

 oxidating fluid, are opposed to a surface 

 of copper. In order to accomplish this, 



