harm, if you were to apply a light to the end of that
pipe before all the air had been swept out of the space above the water. I
am now about to pour in the sulphuric acid. I have used very little zinc,
and more sulphuric acid and water, because I want to keep it at work for
some time. I therefore take care in this way to modify the proportions of
the ingredients, so that I may have a regular supply--not too quick, and
not too slow. Supposing I now take a glass and put it upside-down over the
end of the tube, because the hydrogen is light I expect that it will
remain in that vessel a little while. We will now test the contents of our
glass to see if there be hydrogen in it. I think I am safe in saying we
have caught some [applying a light]. There it is, you see. I will now
apply a light to the top of the tube. There is the hydrogen burning. There
is our philosophical candle. It is a foolish feeble sort of a flame, you
may say; but it is so hot that scarcely any common flame gives out so much
heat. It goes on burning regularly, and I am now about to put that flame
to burn under a certain arrangement, in order that we may examine its
results and make use of the information which we may thereby acquire.
Inasmuch as the candle produces water, and this gas comes out of the
water, let us see what this gives us by the same process of combustion
that the candle went through when it burnt in the atmosphere; and for that
purpose I am going to put the lamp under this apparatus, in order to
condense whatever may arise from the combustion within it In the course of
a short time you will see moisture appearing in the cylinder, and you will
get the water running down the side; and the water from this hydrogen
flame will have absolutely the same effect upon all our tests, being
obtained by the same general process as in the former case. This hydrogen
is a very beautiful substance. It is so light that it carries things up:
it is far lighter than the atmosphere; and I dare say I can shew you this
by an experiment which, if you are very clever, some of you may even have
skill enough to repeat. Here is our generator of hydrogen, and here are
some soap-suds. I have an india-rubber tube connected with the hydrogen
generator, and at the end of the tube is a tobacco-pipe.

[Illustration: Fig. 18.]

I can thus put the pipe into the suds, and blow bubbles by means of the
hydrogen. You observe how the bubbles fall downwards when I blow them with