GALVANISM. 



it will be necessary to add a second 

 copper plate to each pair, so that every 

 cell may contain one zinc and two cop- 

 per plates, the former being placed be- 

 tween the latter. This plan, which was 

 suggested by Dr. Wollaston, was adopt- 

 ed by Mr. Children in the construction 

 of a very large battery, in which each 

 plate was six feet long, by two feet eight 

 inches broad, so that it presented thirty- 

 two square feet of surface.* 



(19.) An ingenious application of this 

 principle was made by Mr. Hart of 

 Glasgow, in the construction of a gal- 

 vanic battery, requiring no other ma- 

 terial for confining the fluid, than the 

 metals themselves which form the 

 circles. This he accomplished by con- 

 verting the double copper plates into 

 cells, by adding sides and bottoms, so as 

 to enable them to hold the acidulous 

 fluid into which the zinc plates are im- 

 mersed. The cells are formed by cut- 

 ting a sheet of copper into the form 

 shown \nfig. 12.t They are then folded 

 Fig 12. 



up as seen in fig. 13, and the seams 

 Fig. 13. 



* Philosophical Transactions for 1815, p. 363. 



t The engraving- fig. 12, is here reduced in its 

 dimensions from the original drawing. It should 

 have been of the size required to form, when folded, 

 .the cell represented in fig. 13. 



grooved. A drop of tin is run into each 

 lower corner to render the cells per- 

 fectly tight. Fig. 14 represents the zinc 



plate, having a piece of screwed brass- 

 wire cast into the top of it for the pur- 

 pose of suspension. Fig. 15 is a section 



Fig. 15. 



of the battery, showing how the copper 

 tail of the first cell is connected with the 

 zinc plate of the second, and so on. 

 The connexion is rendered perfect by 

 joining them with a drop of solder. 

 Each zinc plate is kept firmly in its 

 place by three small pieces of wood. 

 The whole series is then fixed, by means 

 of screw-nuts fitted on to the brass wires, 

 to a bar of baked wood, previously well 

 varnished. When the battery is to be 

 used, it must be lifted off the frame, 

 and dipped into a wooden trough, 

 lined with lead, containing the acid. It 

 is then placed on the frame and is ready 

 for action. Such a battery, with an 

 equal number of zinc plates, is found to 

 possess considerably greater power than 

 the best batteries of the ordinary con- 

 struction.* 



(20.) Various contrivances have been 

 employed for converting a compound 

 voltaic battery, consisting of a certain 

 number of alternations of plates, into a 



* Edinburgh Journal of Science, iv. 19, 



