SSS GALVANISM. 



this vessel are grooves opposite to eacli other, and 

 about a quarter of an inch apart. Into each pair 

 of these opposite grooves is put a plate of zinc and 

 silver, or zinc and copper soldered together. These 

 plates are well fixed in the grooves, in the proper 

 order of copper and zinc, as in the pile, by a cement 

 niade of five parts of resin, four of bees-wax, and 

 two parts of powdered red ochre. This cement 

 must be run in very carefully, so as completely to 

 prevent any communication between the different 

 cells, which would entirely prevent the action of 

 the machine. The cells are then filled with water 

 containing a little acid, common salt, or muriate of 

 ammoniac. 



When a communication is made between the 

 first and last cell, by means of the hands, a strong 

 shock is felt. 



A still better construction of the galvanic battery 

 is as follows. A (Plate 26. fig. 70 ^ s a trough made of 

 earthenware w r ith partitions, into which the diluted 

 acid is put: and alternate plates of zinc and copper, 

 B, are fixed to a bar of wood C, and immersed in 

 the trough, so that a plate of zinc and another of 

 copper shall come into each partition, when the 

 apparatus is used : at other times they are kept out 

 of the trough, and hung upon the uprights, D, E. 

 Thus, the plates are not liable to be so much cor- 

 roded, as in the former construction, and the ap- 

 paratus is more powerful as both the surfaces of the 

 plates are acted upon. It is in this way that the 

 magnificent galvanic apparatus in the Royal Insti- 

 tution is formed, and which was made under the 

 direction of Sir H. Davy. It consists of 2000 

 double plates of zinc and copper 6 inches square, 

 each trough containing 20 plates. It was fre- 

 quently exhibited during his lectures. 



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