r C? Let us call it O--call
it "Oxygen:" it is a very good distinct-sounding name. This, then, is the
oxygen which was present in the water, forming so large a part of it.

We shall now begin to understand more clearly our experiments and
researches; because, when we have examined these things once or twice, we
shall soon see why a candle burns in the air. When we have in this way
analysed the water--that is to say, separated, or electrolysed its parts
out of it--we get two volumes of hydrogen, and one of the body that burns
it. And these two are represented to us on the following diagram, with
their weights also stated; and we shall find that the oxygen is a very
heavy body by comparison with the hydrogen. It is the other element in
water.

I had better, perhaps, tell you now how we get this oxygen abundantly,
having shewn you how we can separate it from the water. Oxygen, as you
will immediately imagine, exists in the atmosphere; for how should the
candle burn to produce water without it?

_____________________
| | |
| 1 | 8 |
| | |
| | Oxygen. | Oxygen, . . . . 88.9
| | |
| |_________| Hydrogen, . . . 11.1
| Hydrogen. | -----
| | 9 Water,. . . . . 100.0
| |
| |
| |
|___________|

Such a thing would be absolutely impossible, and chemically impossible,
without oxygen.

[Illustration: Fig. 21.]

Can we get it from the air? Well, there are some very complicated and
difficult processes by which we can get it from the air; but we have
better processes. There is a substance called the black oxide of
manganese: it is a very black-looking mineral, but very useful, and when
made red-hot it gives out oxygen. Here is an iron bottle which has had
some of this substance put into it, and there is a tube fixed to it, and a
fire ready made, and Mr. Anderson will put that retort into the fire, for
it is made of iron, and can stand the heat. Here is a salt called chlorate
of potassa, which is now made in large quantities for bleaching, and
chemical and medical uses, and for pyrotechnic and other purposes. I will
take some and mix it with some of the oxide of manganese (oxide of copper,
or oxide of iron would do as well); and if I put these together in a
retort, far less than a red heat is sufficient to evolve this oxygen from
the mixture. I am not preparing to