containing the water; and you see the bubbles rising: let us
collect these bubbles and see what they are. Here is a glass cylinder (O);
I fill it with water and put it over one end (A) of the pile; and I will
take another (H) and put it over the other end (B) of the pile. And so now
we have a double apparatus, with both places delivering gas. Both these
jars will fill with gas. There they go, that to the right (H) filling very
rapidly; the one to the left (O) filling not so rapidly; and though I have
allowed some bubbles to escape, yet still the action is going on pretty
regularly; and were it not that one is rather smaller than the other, you
would see that I should have twice as much in this (H) as I have in that
(O). Both these gases are colourless; they stand over the water without
condensing; they are alike in all things--I mean in all _apparent_ things;
and we have here an opportunity of examining these bodies and ascertaining
what they are. Their bulk is large, and we can easily apply experiments to
them. I will take this jar (H) first, and will ask you to be prepared to
recognise hydrogen.

Think of all its qualities--the light gas which stood well in inverted
vessels, burning with a pale flame at the mouth of the jar--and see
whether this gas does not satisfy all these conditions. If it be hydrogen,
it will remain here while I hold this jar inverted. [A light was then
applied, when the hydrogen burnt] What is there now in the other jar? You
know that the two together made an explosive mixture. But what can this
be which we find as the other constituent in water, and which must
therefore be that substance which made the hydrogen burn? We know that the
water we put into the vessel consisted of the two things together. We find
one of these is hydrogen: what must that other be which was in the water
before the experiment, and which we now have by itself? I am about to put
this lighted splinter of wood into the gas. The gas itself will not burn,
but it will make the splinter of wood burn. [The Lecturer ignited the end
of the wood, and introduced it into the jar of gas.] See how it
invigorates the combustion of the wood, and how it makes it burn far
better than the air would make it burn; and now you see by itself that
every other substance which is contained in the water, and which, when the
water was formed by the burning of the candle, must have been taken from
the atmosphere. What shall we call it, A, B, o