CHAPTER XII 



THE CONSTRUCTION OF SIMPLE VOLTAIC CELLS 



THE facts to be described in this chapter and the next refer to 

 the production of electric currents by means of simple voltaic 

 cells, and to chemical changes which such electric currents are 

 able to produce. In order to obtain a clear idea of the use 

 of the various materials employed in the construction of voltaic 

 cells, and the chemical effects to which electric currents are able 

 to give rise, it is necessary to know something about the principles 

 of chemistry. This chapter and the following one will, therefore, 

 be more profitably read if they are taken after the section on 

 chemistry than if they are studied at this stage. 



Fundamental Experiments. EXPT. 176. Prepare some 

 dilute sulphuric acid containing one part of strong acid to 

 eight parts of water. First measure out the water into a large 

 beaker, and then gently pour the measured quantity of strong 

 acid into the water, keeping the latter briskly stirred with a 

 glass stirring rod. Having noticed the large amount of heat 

 generated set the mixture on one side to cool. 



EXPT. 177. Plunge a strip of ordinary commercial zinc into 

 a beaker of cold dilute sulphuric acid prepared as in the last 

 experiment. Notice the brisk evolution of gas which takes 

 place. What gas is given off ? (See p. 189.) 



EXPT. 178. Repeat Expt. 177, substituting first a rod of 

 pure zinc and then a strip of copper. Observe that there is 

 no chemical action (p. 189) in either case. 



EXPT. 179. Place the rod of pure zinc and the strip of 

 copper into the dilute acid, taking care that the two metals 

 do not touch one another. No gas is given off from either 

 .metal. 



