CHAPTER X.. Expansion From Heat.

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.