134 CORRELATION OF THE PHYSICAL FORCES. 



and beautiful manner. Here are some pieces 

 of zinc covered with mercury, exactly in the 

 same way as the zinc in that retort is covered ; 

 and if I put this plate into sulphuric acid I get 

 no gas, but this most extraordinary thing occurs, 

 that if I introduce along with the zinc another 

 metal which is not so combustible, then I re- 

 produce all the action. I am now going to put 

 to the amalgamated zinc in this retort some 

 portions of copper wire (copper not being so 

 combustible a metal as the zinc), and observe 

 how I get hydrogen again, as in the first 

 instance there, the bubbles are coming over 

 through the pneumatic trough, and ascending 

 faster and faster in the jar; the zinc now is 

 acting by reason of its contact with the copper. 

 Every step we are now taking brings us to a 

 knowledge of new phenomena. That hydrogen 

 which you now see coming off so abundantly 

 does not come from the zinc as it did before, 

 but from the copper. Here is a jar containing 

 a solution of copper. If I put a piece of this 

 amalgamated zinc into it, and leave it there, it 

 has scarcely any action, and here is a plate of 

 platinum which I will immerse in the same 

 solution, and might leave it there for hours, 



