358 THE POPULAR SCIENCE MONTHLY. 



Furthermore, pieces of the same metal under different physical 

 conditions, when combined with each other, will give a current. 

 For instance, a piece of polished iron opposed to a rusty piece 

 gives a current, and a plate of very rusty lead, if I may use the 

 expression, combined with a piece of bright lead yields even more 

 current than zinc and carbon. Unfortunately, lead does not rust 

 sufficiently well to suit electricians, and other physical reasons 

 prevent its being used in primary batteries. 



It will thus be seen that a storage battery, when once charged, 

 becomes nothing more or less than a primary battery. In the 

 case before described, after charging, we have zinc and copper in 

 a solution of zinc sulphate. 



In describing the effects of electricity in passing through an 

 electrolyte, we have assumed that the liquid contained a metal 

 in solution. Suppose, now, that we take water, which has no 

 metal in it, and subject it to the action of the current. The elec- 

 tricity can get no metal to deposit on the wire, where it passes 

 out, and in consequence does the next "best thing and leaves one 

 of the components of the water viz., hydrogen gas. The other 

 component, oxygen, collects around the entrance wire. The Eng- 

 lish physicist Grove showed that, if these two wires, around which 

 the gases had collected, were connected together, a current of elec- 

 tricity would flow the same as if there were two metals instead of 

 two gases. Now, water is cheap, and if there were not some 

 serious technical difficulties as regards efficiency, Grove's battery 

 would be universally employed. 



It was reserved, however, for M. Gaston Plants to construct 

 the first practical secondary battery. He considered the follow- 

 ing points in its construction : Water is cheap ; water, when sub- 

 jected to the electric current, gives off oxygen and hydrogen; 

 rusty lead, when combined with bright lead, has a high electro- 

 motive force ; oxygen makes lead rusty and hydrogen makes it 

 bright. His battery consisted, then, of two lead plates suspended in 

 water, which contained a little sulphuric acid to assist in the con- 

 duction. When a current of electricity was passed through, hy- 

 drogen was thrown off at one plate, making it bright, and oxygen 

 at the other plate, peroxidizing its surface. When the charging 

 source was removed, the altered plates would send off a current, 

 which was in a direction opposite to the one which had charged 

 them, and this would keep up until the plates had assumed their 

 original condition. 



Plante's choice of materials was most wise, and all practical 

 storage batteries of to-day are but modifications of his style. 



In order that his battery might give a strong current, and one 

 that would last a long time, it was found necessary that his two 

 lead plates should be as near to each other, and that they should 



