292 



SCIENCE OF COMMON THINGS. 



Poles of a battery. Means by which galvanic-electricity in quantity can be developed. 

 1897* What do we mean when we speak of a galvanic circuit ? 



The connection of the two metals in the battery, so 

 that the positive and negative electricities can meet, 

 and flow in opposite directions. 



1898 At what point in the circuit will the manifestations of electricity 

 be most apparenl ? 



At the point where the two currents meet. 



' 1899 What is meant by the poles of the battery ? 



The two metals forming the elements of the battery 

 are generally connected by copper wires ; the ends of 

 these wires, or the terminal points of any other connect- 

 ing medium used, are called the poles of the battery. 



Thus, when zinc and copper poles are used, the end of the wire con- 

 veying positive electricity from the zinc would be the pbsitive pole, and 

 the end of the wire conveying negative electricity from the copper plate 

 would be the negative pole. Faraday describes the poles of the battery 

 as the doors by which electricity enters into or passes out of the substance 

 suffering decomposition. 



A very simple, and at the same time an active, galvanic circuit may be 

 formed by an arrangement as re- 

 presented in Fig. 87. C and Z are 

 thin plates of copper and zinc im- 

 mersed in a glass vessel containing 

 a very weak solution of sulphuric 

 acid and water. Metallic contact 

 is made by means of the" wires, X 

 and W, soldered to the plates, the 

 poles intersecting at Y. The cur- 

 rent of positive electricity, when 

 the circuit is closed, passes from 

 the zinc, through the liquid, to the 

 copper, and from the copper, along 

 the conducting wires, to the zinc, 

 as indicated by the arrows in the 

 figure. A current of negative elec- 

 tricity traverses the circuit also, Fig. 87. 

 from the copper to the zinc, in a 

 direction precisely reversed. 



1900 By lohat chemical action can the greatest abundance of galvanic 

 electricity be developed ? 



By the oxidation of metallic zinc by weak sulphuric 

 acid. 



01 Ol The electricity developed by the action of a single pair of plates 

 immersed in acid water is very feeble : how can it be increased ? 



By increasing the number of the plates and the quan- 



