CHAPTER XIII 



CHEMICAL CHANGE INDUCED BY THE ELECTRIC CURRENT 



How the Passage of an Electric Current can be recognised. 

 The Galvanoscope. Before proceeding to study the chemical 

 changes induced by an electric current it is very desirable that 

 a method should be learnt by means of which the passage of a 

 current of electricity through a circuit can easily be perceived. 

 Expt. 191 provides such a means, and if it be modified somewhat 

 we are in possession of a sure plan of recognising even small 

 currents. 



EXPT. 191. Instead of a single wire such as was used 

 in Expt. 184, substitute an arrangement like that shown in 



Fig. 103, where a light magnetic 

 needle hangs inside a coil of 

 wire. The effect of coiling the 

 wire is, roughly, to multiply 

 the effect of the single wire by 

 the number of turns there is in 

 the coil. Connect the ends of 

 the coil with a copper and an 

 amalgamated zinc plate and dip 

 the plates into dilute sulphuric 

 acid. Compare the effect on the 

 needle in this case with that 

 obtained by passing the current 

 along a single wire. 



EXPT. 192. Substitute an astatic pair for the single mag- 

 netic needle in the last experiment. The astatic pair consists 

 of two equally strong magnets arranged parallel to one 

 another, with opposite poles in the same direction, and per- 



PIG. 103. A Galvanoscope. 



