396 NINETEENTH CENTURY. FT. ill. 



upon each other, as Volta thought, but is caused by the 

 chemical action going on between the zinc and the water. 

 '1 hus, if you put some zinc in sulphuric acid and water, the 

 zinc pulls the water to pieces, and hydrogen gas comes 

 bubbling off, but if you coat the zinc with mercury, hydrogen 

 will no longer come off, and no action will take place till 

 you put another metal in the water, as for example a piece 

 of copper, and connect the two metals by a wire. Then the 

 hydrogen bubbles off again, but this time it does not come 

 off the zinc, but off the copper. The force which overcomes 

 the chemical attraction in the water has been made to travel 

 across the vessel from one metal to the other, and this 

 journey may be made as long a one as you choose, and may 

 even be continued for hundreds of miles if only the current 

 has some means of finding its way home to the first metal 

 at last. 



Now all this is a modified result of the chemical action 

 of the zinc and acid water upon each other; as Faraday 

 proved in a most beautiful way by showing that the power 

 of the electric current to decompose water in another vessel 

 depends entirely upon the violence of the action going on 

 between these two elements of the battery. If the battery 

 is weak, the water in which the ends of the wires are dipped 

 is decomposed slowly ; if the battery is strong, the bubbles 

 of oxygen and hydrogen come off rapidly and vehemently. 

 This led him to invent a useful little instrument called a 

 voltameter, which measures the quantity of water decom- 

 posed, and so tells exactly what is the strength of the electric 

 current. Thus we see/ says Faraday in one of his lectures, 

 ' that the power which decomposes water, or produces the 

 heat and light of the electric spark, is neither more nor less 

 than the chemical force of the zinc its very force carried 

 along the wires and conveyed to another place.' 



