EXPANSION FROM HEAT.
_(Continued.)_
Q. _Does heat expand every thing ELSE BESIDES air and water?_
A. Yes; _every_ thing (that man is acquainted with) is expanded by heat.
Q. _Why does a COOPER make his HOOPS RED-HOT, when he puts them on a
tub?_
A. 1st--As _iron expands by heat_, the hoops will be _larger_ when they
are red-hot; and will, therefore, _fit more easily on the tub_: and
2ndly--As _iron contracts by cold_, the hoops will _shrink_ as they cool
down, and _girt the tub with a tighter grasp_.
Q. _Why does a WHEELWRIGHT make his hoops RED-HOT, which he fixes on the
NAVE of a WHEEL?_
A. 1st--That they may _fit on more easily_: and
2ndly--That they may _girt the nave more tightly_.
Q. _Why will the wheelwright's HOOP FIT the nave MORE EASILY, because
they are made RED-HOT?_
A. As _iron expands by heat_, the hoops will be _larger_ when they are
hot; and (being larger) will go on the nave more _easily_.
Q. _Why will the HOOPS, which have been PUT ON HOT, girt the nave more
FIRMLY?_
A. As _iron contracts by cold_, the hoops will _shrink as they cool
down_; and, therefore, _girt the nave with a tighter grasp_.
Q. _Why does a farrier put the HORSE-SHOE on HOT?_
A. That it may _stick the closer_, when it has contracted by cold.
Q. _Why does a STOVE make a CRACKING NOISE, when a fire is very hot?_
A. The iron stove _expands by heat_, and (as it swells) the parts rub
both _against each other_, and _against the bricks around_, driving them
further off; and this produces a _cracking_ noise.
Q. _Why does a STOVE make a similar CRACKING NOISE, when a large FIRE is
TAKEN DOWN?_
A. The iron stove _contracts again_, as soon as the fire is removed;
and (as it shrinks into a smaller space) the parts _rub against each
other again_, and the _bricks are again disturbed_; and this produces a
cracking noise.
Q. _Why does the PLASTER round a STOVE CRACK and fall away?_
A. When the fire is lighted, _the iron-work_ (which expands more than
the brick-work and plaster) _pushes away the bricks and plaster_: but
when the fire is put out, the metal _shrinks_ again, and _leaves the
"setting" behind_.
Q. _Why does the PLASTER FALL AWAY?_
A. As a _chink_ is left (between the "setting" and the stove), the
plaster will frequently fall away _from its own weight_.
Q. _What OTHER cause contributes to BRING the PLASTER DOWN?_
A. As the _heat of the fire_ varies, the _size of the iron stove_ varies
also; and this swelling and perpetually contracting, keeps up such a
_constant disturbance about the plaster_, that it _cracks and falls
off_, leaving the fire-place very unsightly.
Q. _Why does the MERCURY of a THERMOMETER RISE in hot weather?_
A. Heat _expands the metal_; and as the metal is _increased in bulk_, it
occupies a _larger space_, (or, in other words, rises higher in the
tube.)
Q. _Why is a GLASS BROKEN, when HOT WATER is poured into it?_
A. Because the _inside of the glass_ is expanded by the hot water, and
_not the outside_; so the glass _snaps_ for want of _flexibility_.
Q. _Why is not the OUTSIDE of the GLASS expanded by the hot water, as
well as the INSIDE?_
A. Glass is a _non-conductor of heat_; and, therefore, _breaks_ before
the heat of the _inner surface_ is _conducted to the outside_.
Q. _Why does a GLASS snap, because the INNER surface is HOTTER than the
OUTER?_
A. _Glass is expanded by heat_; and as the inner surface expands, _it
stretches the outer surface till it snaps_.
Q. _Why is a CHINA CUP broken, if HOT WATER be poured over it, or into
it?_
A. China is a _non-conductor_; and, as the _inner surface expands by the
heat_, before the _outer one_, _it forms an arch_, and pulls the parts
of the cup asunder.
Q. _Why does the BOTTOM COME OFF, if a GLASS BEAKER be set on a warm
HOB?_
A. Glass is a _non-conductor_; and, as the _bottom of the glass_ (from
the warmth of the hot stove) _expands, before the sides are heated_, the
two parts _separate_ the one from the other.