PRACTICAL PHYSIOLOGY 



the copper inside. 1 The amount of this current 

 depends upon the difference of potential produced 

 within the cell. This is diminished by any in- 

 crease of resistance to the flow of electricity 

 whether occurring within the cell or in the outside 

 circuit. Electromotive force (E.M.F.) is measured in 

 volts ; thus the E.M.F. of a Daniell cell is 1.079 volts. 



Anode.. 



Copper, 



Kathode. 



Zinc. 



mmm .Dilute sulphuric acid. 



FIG. i. VOLTAIC COUPLE. 



It may be increased by coupling two or more cells 

 together in series, the zinc of one connected with 

 the copper of the next, and so on. 



If electricity be generated simply by immersing 

 plates of zinc and copper into acid the chemical 

 action which ensues causes bubbles of hydrogen 



1 Within the battery the electrical potential is highest at the 

 zinc, which is therefore here the anode, and lowest at the copper, 

 which is here the kathode. 



