198 ESSAYS BIOGRAPHICAL AND CHEMICAL 



trons ; and the copper, like the zinc, is overloaded by the 

 electrons from the zinc. Hence it transmits them to the 

 copper plate, and they find their way to the surface of the 

 plate. 



There they find hydrogen ions, which are ready to com- 

 bine each with one electron in order to form hydrogen 

 atoms ; and having combined, the atoms of hydrogen 

 unite in couples, bubbles of hydrogen are formed, and 

 float up to the surface and burst. In short, the zinc 

 passes on its electrons through the copper wire to the 

 copper plate, when they are transmitted to the ions of 

 hydrogen in solution, and these first become atoms and 

 then molecules. 



These conceptions, which are rather intricate, may be 

 rendered clearer by means of a diagram, a is the solu- 

 tion of hydrochloric acid in water ; b is the zinc plate ; 

 c is the copper plate, and d the connecting wire. H H, on 

 the left of the diagram, are two atoms of hydrogen, each 



c b 



EXPLANATION OF A GALVANIC CELL 



of which has gained an electron ; they will unite together 

 to a molecule, and escape in a bubble up through the 



