should have thought, as blood out of a post. Where does it come from?"

"Part from the wax, and part from the air, and yet not a drop of
it comes either from the air or the wax. What do you make of that,
uncle?"

"Eh? Oh! I'm no hand at riddles. Give it up."

"No riddle at all, uncle. The part that comes from the wax isn't
water, and the part that comes from the air isn't water, but when put
together they become water. Water is a mixture of two things then.
This can be shown. Put some iron wire or turnings into a gun barrel
open at both ends. Heat the middle of the barrel red-hot in a little
furnace. Keep the heat up, and send the steam of boiling water through
the red-hot gun barrel. What will come out at the other end of the
barrel won't be steam; it will be gas, which doesn't turn to water
again when it gets cold, and which burns if you put a light to it.
Take the turnings out of the gun-barrel, and you will find them
changed to rust, and heavier than when they were put in. Part of the
water is the gas that comes out of the barrel, the other part is what
mixes with the iron turnings, and changes them to rust, and makes
them heavier. You can fill a Wadder with the gas that comes out of
the gun-barrel, or you can pass bubbles of it up into a jar of water
turned upside down in a trough, and, as I said, you can make this part
of the water burn."

"Eh?" cried Mr. Bagges. "Upon my word! One of these day, we shall have
you setting the Thames on fire."

"Nothing more easy," said Harry, "than to burn part of the Thames, or
of any other water; I mean the gas that I have just told you about,
which is called hydrogen. In burning, hydrogen produces water again,
like the flame of a candle. Indeed, hydrogen is that part of the water
formed by a candle burning, that comes from the wax. All things that
have hydrogen in them produce water in burning, and the more there
is in them the more they produce. When pure hydrogen burns, nothing
comes from it but water, no smoke or soot at all. If you were to burn
one ounce of it, the water you would get would be just nine ounces.
There are many ways of making hydrogen besides out of steam by the
hot gun-barrel. I could show it you in a moment by pouring a little
sulphuric acid mixed with water into a bottle upon a few zinc or steel
filings, and putting a cork in the bottle with a little pipe through
it, and setting fire to the gas that would come from the mouth of
the pipe. We should f