222 



SCIENTIFIC RECREATIONS. 



is at the bottom and a disc of zinc at the top. The latter, P, is the positive 

 pole ; the former, N, the negative. When the wires are united the current is 

 closed, and no sign of disturbance can be detected, although the action, of 

 course, is proceeding within the pile. The opposite kinds of electricity 

 neutralize each other, and if a continuous supply were not kept up the 

 electricity would disappear ; but as it is, a powerful current is obtained, and if 

 the wire be divided a spark will be observed. 



tig. 222. Cunsen Battery 



There are many forms of galvanic batteries. The Trough Battery ot 

 Cruickshank has been mentioned. There is Wollaston's Pile, Bunsen's 

 Battery, Grove's Battery, and Daniell's, called the " Constant " Battery. In 

 this last a porous earthenware cell is placed within a cylinder of copper ; in 

 the cell a rod of zinc is inserted, the cell being filled with diluted sulphuric 

 acid, one part of acid to ten parts of water, and in the outer cylinder 

 is a solution of sulphate of copper. 



223. Daniell's Battery. 



Fig. 224. Grove ; s Battery. 



the 

 the 



The cut above illustrates Daniell's Battery (fig. 223) with connectors. 

 In Bunsen's Battery (or the Zinc-Carbon Battery), which is very like 

 " Daniell " arrangement, as will be seen from the plates (figs. 222, 223), 

 porous cell has a prism of carbon immersed in it, and is apparently 

 a modification of the powerful "Grove" Battery (fig. 224). This consists of 

 slips of platinum, //, placed in porous cells, g, each cell being surrounded by 

 a glass cylinder. The outer (glass) cells are filled, or nearly filled, with 

 diluted sulphuric acid ; nitric acid is used in the porous cells, and a platinum 

 plate inserted. The chemical action of the Grove cell is thus explained by 



