134 ELEMENTS OF SCIENCE 



termed alkaline substances, each of which latter is also 

 called a base. Bodies composed of an acid and a base 

 are termed " salts." Now if the two poles (the ends of 

 the wires) of an electric pile or battery be placed in 

 water so that the electricity may be conducted through 

 it from one pole to the other, and any " salts " be dis- 

 solved in that water, we shall find the solution breaks up, 

 the acid matter going to the positive pole, and the base, 

 or alkaline constituent, to the negative pole. This 

 strikingly demonstrates the close connection which 

 exists between electrical and chemical energy. The 

 quantity of electricity generated by chemical changes 

 is often enormous. It has been said that the resolution 

 of a grain of water will generate a quantity equal 

 to a flash of lightning. As in the generation of 

 heat, light and magnetism by chemical energy, so also 

 in its generation of electricity, the quantity generated 

 bears a constant and exact relation to the amount of 

 chemical energy expended. 



The mode in which electricity is most commonly and 

 effectively generated by chemical energy and a powerful 

 electric current induced, is by what are called electric 

 batteries and piles. The simplest and most primitive 

 form of the electric pile consists of a series of discs of 

 zinc and copper, separated by discs of cloth soaked with 

 vinegar, and with two wires fastened to the series. One 

 of these wires must touch a disc of copper at one end of 

 the pile and the other must be in contact with a disc of 

 zinc at the other end of the pile, while each wire projects 

 freely at its other end. The chemical energy excited 

 by the contact of the substances in the pile gives rise 

 to electricity, and therefore to both its so-called kinds. 

 The positive kind goes exclusively to the wire which 

 touches the copper, while that from the zinc receives 



