Page:On the various forces of nature and their relations to each other.djvu/155

Rh have not destroyed the power of chemical affinity, but modified it in a wonderful 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 reproduce 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