A. Heat communicated by being carried to another thing or place; as the hot water resting on the bottom of a kettle, carries heat to the water through which it passes. (see p. 246).

A. No; liquids are bad conductors; and are, therefore, made hot by convection.

A. Because heat converts a liquid into steam, and flies off with the vapour, instead of being conducted through the liquid.

A. The water nearest the fire is first heated, and (being heated) rises to the top; other cold water succeeds, is also heated, and rises in turn; and this interchange keeps going on, till all the water boils.

A. This commotion is mainly produced by the ascending and descending currents of hot and cold water.

The escape of air from the water contributes also to increase this agitation.

A. The hot ascending current passes close by the metal sides of the kettle; while the cold descending current passes down the centre.

A. The bubbles are portions of steam (formed at the bottom of the vessel) which rise to the surface, and escape into the air.

A. As the heat insinuates itself between the particles of water, it drives them asunder; and (as the particles of water are driven apart from each other) the same vessel will no longer hold the expanded water, and some runs over.

A. Water contains a great deal of air, which (being expanded by the heat of the fire) escapes by fits through the spout of the kettle; which sings in the same way as a trumpet does, when a person blows in it.

A. Boiling is the effect of a more violent escape of air from the heated water; when, therefore, the air is not permitted to escape, water will never boil.

A. Because the heated water always ascends to the surface, heating the water through which it passes: if, therefore, heat were applied to the top of a vessel, the water below the surface would never be heated.

A. The iron of a grate is an excellent conductor; and, therefore, if one part be heated, the heat is conducted to every other part: but water is a very bad conductor, and will not diffuse heat in a similar way.

A. When a blacksmith immerses his red-hot iron in a tank of water, the water which surrounds the red-hot iron is made boiling hot, but the water below the surface remains quite cold.

A. To the top of the liquid; because the cold portion will always descend, and allow the warmer parts to come in contact with the cooling substance.

A. No; not if the steam be suffered to escape.

A. Because as fast as the water boils, it is converted into steam; and the steam carries away the additional heat, as fast as it is communicated.

A. Steam is invisible; but when it comes in contact with the air (being condensed into small drops) it instantly becomes visible.

A. If you look at the spout of a boiling kettle, you will find that the steam (which issues from the spout) is always invisible for about half an inch; after which, it becomes visible.

A. The air is not able to condense the steam as it first issues from the spout, but when it spreads and comes in contact with a larger volume of air, the invisible steam is readily condensed into visible drops.

A. Because it is condensed by the cold air into small drops, which are visible to the eye.

A. Steam is very elastic; and this elasticity increases in a greater proportion than the heat which produces it; unless, therefore, some vent be freely allowed, the steam heaves and swells, till it bursts the vessel which confined it.

A. It is dissolved by the air, and forms a part of its invisible vapour.

A. No; air is a very bad conductor, and is heated (like water) by convection.

A. The air nearest the fire is made hot first; the cold air descends, is heated also, and rises in turn; and this goes on, till all the air of the room is warmed.

A. As heated air always ascends, if the fire were not near the floor, the lower part of the air (which we want to be the warmest) would never be benefited by the fire at all.

A. Because the hot end of the poker heats the air around it, and this hot air (in its ascent) scorches the poker, and the hand which holds it.

A. With the hot end upwards; because then the air (heated by the poker) would not pass over our hand to scorch it.

A. The poker is an excellent conductor; while, therefore, it rests against the hot stove, the heat of the stove is conducted into the poker; but when it rests on the fender, it does not come in contact with the hot stove.

A. Not being so warm as our hand, it imbibes the heat from it with such rapidity, that our loss of heat is palpable, and produces the sensation of coldness.

A. In order that the heat of the flue may be more readily diffused throughout the room. Black lead radiates heat more freely than any other known substance.

A. The thick end of an egg always contains a little air (between the shell and the white); but, when the egg is stale, the white shrinks, and the air expands.

A. As air is a very bad conductor, if the egg be stale, it will feel much warmer to the tongue, than if it be new-laid.

A. As air is a bad conductor, it will draw off the heat of the tongue very slowly, and, therefore, appear warm; but when there is only a very little air in the egg (as the white is a pretty good conductor), the heat of the tongue will be more rapidly drawn off, and the egg appear colder.

A. To let the air out; if the large end were not cracked, the air (expanded by the heat) would enter the white of the egg, and give it an offensive taste.