That you may understand the character and use of this instrument, let us
make an experiment or two. Let us put together, first of all, some
substances, knowing what they are, and then see what that instrument does
to them. There is some copper (observe the various changes which it can
undergo), and here is some nitric acid, and you will find that this, being
a strong chemical agent, will act very powerfully when I add it to the
copper. It is now sending forth a beautiful red vapour; but as we do not
want that vapour, Mr. Anderson will hold it near the chimney for a short
time, that we may have the use and beauty of the experiment without the
annoyance. The copper which I have put into the flask will dissolve: it
will change the acid and the water into a blue fluid, containing copper
and other things; and I propose then shewing you how this voltaic battery
deals with it; and in the mean-time we will arrange another kind of
experiment for you to see what power it has. This is a substance which is
to us like water--that is to say, it contains bodies which we do not know
of as yet, as water contains a body which we do not know as yet. Now, this
solution of a salt[15] I will put upon paper, and spread about, and apply
the power of the battery to it, and observe what will happen. Three or
four important things will happen which we shall take advantage of. I
place this wetted paper upon a sheet of tinfoil, which is convenient for
keeping all clean, and also for the advantageous application of the power;
and this solution, you see, is not at all affected by being put upon the
paper or tinfoil, nor by anything else I have brought in contact with it
yet, and which, therefore, is free to us to use as regards that
instrument. But first let us see that our instrument is in order. Here are
our wires. Let us see whether it is in the state in which it was last
time. We can soon tell. As yet, when I bring them together, we have no
power, because the conveyers--what we call the electrodes--the passages or
ways for the electricity--are stopped; but now Mr. Anderson by that
[referring to a sudden flash at the ends of the wires] has given me a