and twelve degrees and one thousand degrees
is seven hundred and eighty-eight degrees;
and what has become of all this heat? Why,
it is entirely contained in the steam, though it
does not make the steam hotter. It lies hid
in the steam, and therefore it is called latent
heat. When the steam is condensed, all that
latent heat comes out of it, and can be felt,
and the quantity of it can be measured by a
thermometer. The warmth that issues from
steam-pipes used to warm a house, is the
latent heat of the steam that escapes as the
steam turns back to water."

"Latent heat! latent heat! " repeated Mr.
gges, scratching his head. "Eh? Now,
that latent heat always puzzles me. Latent,
lying hid. But how can you hide heat?
When the zany in the pantomime hides the
red-hot poker in his pocket, he cauterises
his person. How—eh?—how can heat be
latent?"

"Why, the word heat has two meanings,
uncle. In the first place, it means hotness.
Hotness cannot be latent, as the clown finds
when he pockets the poker. In the second
place, heat means a something the nature of
which we don't know, which is the cause of
hotness, and also the cause of another effect.
Whilst it is causing that other effect, it does
not cause hotness. That other effect which
heat causes in the instance of steam, is keeping
water in the form of steam. The heat
that there is in steam, over and above two
hundred and twelve degrees, is employed in
this way. It is wholly occupied in preserving
the water in an expanded state, and can't
cause the mercury in the thermometer to
expand and rise as well. For the same reason,
it could give you no feeling of hotness above
what boiling water would—if you had the
nerve to test it. Whilst it is making steam
continue to be steam, it is latent. When the
steam becomes water again, it has no longer
that work to do, and is set free. Free heat is
what is commonly understood by heat. This
is the heat which cooks our victuals, the heat
we feel, the heat that singes Mr. Merriman.
Latent heat is heat that doesn't warm, singe,
or cook, because it is otherwise engaged. If
you press gas suddenly into a fluid, the latent
heat of the gas is set free. You seem to
squeeze it out. Indeed, the same thing ?
happens, if you violently force any substance into
a closer form all at once. Everything appears
to have more or less latent heat in it, between
its little particles, keeping them at certain
distances from each other. Compress the
particles within a smaller compass, and a part
of the latent heat escapes, as if it were no
longer wanted. When a substance in a
compressed state expands on a sudden, it draws
in heat, on the other hand. When a lady
bathes her forehead with eau-de-Cologne to
cure a headache, the heat of the head enters
the eau-de-Cologne, and becomes latent in it
whilst it evaporates. If you make steam under
high pressure, you can heat it much above
two hundred and twelve degrees. Suppose
you let off steam, so compressed and heated,
by a wide hole, from the boiler, and put your
hand into it as it rushes out"——

"What? Why, you'd scald your hand off!"
cried Mr. Bagges.

"No, you wouldn't. The steam rushes out
tremendously hot, but it expands instantly so
very much, that the heat in it directly becomes
latent in a great measure; which cools it
down sufficiently to allow you to hold your
hand in it without its hurting you. But
then you would have to mind where you
held your hand; because where the steam
began to condense again, it would be boiling
hot."

"I had rather take your word for the
experiment than try it, young gentleman,"
Mr. Bagges observed.

"Another very curious thing," proceeded
Harry, "in regard to boiling, has been discovered
lately. A kettle might be too hot to boil
water in. Take a little bar of silver, heated
very highly; dip it into water. At first, you
have no boiling, and you don't have any at all
till the silver has cooled some degrees. Put
a drop of water into a platinum dish, heated
in the same way, and it will run about without
boiling till the heat diminishes; and then it
bursts into steam. M. Boutigny, the French
chemist, made this discovery. Vapour forms
between the drop of water and the red-hot
metal, and, being a bad conductor of heat,
keeps the heat of the metal for some time
from flowing into the water. Owing to this,
water, and mercury even, may be frozen in a
red-hot vessel if the experiment is managed
cleverly. A little more than a couple of
centuries ago, this would have been thought
witchcraft."

"And the philosopher," added Mr. Bagges,
would have been fried instead of his water-
drop. Let me see—eh?—what do they call
this singular state of water?"

"The spheroidal state," answered Harry.
"However, that is a state that water does not
get into in a kettle, because kettles are not
allowed to become red hot, except when they
are put carelessly on the fire with no water
in them, or suffered to remain there after the
water has boiled quite away!"

"Which is ruination to kettles," Mrs.
Wilkinson observed.

"Of course it is, mamma, because at a red
heat iron begins to unite with oxygen, or to
rust. Another thing that injures kettles is
the fur that collects in them. All water in
common use contains more or less of earthy
and other salts. In boiling, these things
separate from the water, and gradually
form a fur or crust inside the kettle or
boiler."

"And a nice job it is to get rid of it," said
his mamma.

"Well; chemistry has lessened that
difficulty," replied Harry. "The fur is mostly
carbonate of lime. In that case, all you have