placed on the top of the fire, its blaze would afford no contact of flame to fuel lying below.
Q. Why should coal be placed above the wood?
A. As every flame tends upwards, if the wood were above the coal, the flame would not rise through the coal to heat it.
Q. Why is a fire kindled at the lowest bar of a grate?
A. As every flame tends upwards; when a flame is made at the bottom of a fire, it ascends through the fuel and heats it: whereas, if the fire were lighted from the top, the flame would not come into contact with the fuel piled below.
Q. Why does coal make such excellent fuel?
A. Because it is so very hard and compact, that it burns away very slowly.
Q. Why will cinders become red hot, quicker than coals?
A. Because they are more porous and less solid; and are, therefore, sooner reduced to a state of combustion.
Q. Why will not iron cinders burn?
A. Iron cinders are cinders saturated with oxygen; they are unfit for fuel, because they can imbibe no more oxygen, being saturated already.
Q. Why are cinders lighter than coals?
A. Because their vapour, gases, and volatile parts, have been driven off by previous combustion.
Q. Why will not stones do for fuel, as well as coals?
A. Because they contain no hydrogen (or inflammable gas) like coals.
Q. Why will not wet kindling light a fire?
A. 1st—Because the moisture of the wet kindling prevents the oxygen of the air from getting to the fuel to form it into carbonic acid gas: and
2ndly—The heat of the fire is perpetually drawn off, by the conversion of water into steam.
Q. Why does dry wood burn better than green?
A. 1st—Because no heat is carried away, by the conversion of water into steam: and
2ndly—The pores of dry wood are filled with air, which supply the fire with oxygen.
Q. Why do two pieces of wood burn better than one?
A. 1st—Because they help to entangle the heat of the passing smoke, and throw it on the fuel: and
2ndly—They help to entangle the air that passes over the fire, and create a kind of eddy or draught.
Q. Why does salt crackle when thrown into a fire?
A. Salt contains water; and the cracking of the salt is owing to the sudden conversion of the water into steam.
Q. Why will not wood or paper burn, if they are steeped in a solution of potash, phosphate of lime, or ammonia (hartshorn)?
A. Because any “al’kali” (such as potash) will arrest the hydrogen (as it escapes from the fuel), and prevent its combination with the oxygen of air.
Q. What is an al’kali?
A. The con’verse of an acid; as bitter is the con’verse of sweet, or insipid the con’verse of pungent.
Q. Why does a jet of flame sometimes burst into the room through the bars of a stove?
A. The iron bars conduct heat to the interior of some lump of coal: and its volatile gas (bursting through the weakest part) is kindled by the glowing coals over which it passes.
Q. Why is this jet sometimes of a greenish yellow colour?
A. When a lump of coals lies over the hot bars, or the coals below it are not red hot, the gas which bursts from the lump escapes unburnt, and is of a greenish colour.
Q. Why does the gas escape unburnt?
A. Because neither the bars nor coals (over which it passes) are red-hot.
Q. Why does a bluish flame sometimes flicker on the surface of hot cinders?
A. Gas from the hot coals at the bottom of the grate mixing with the carbon of the coals above, produces an inflammable gas (called carbonic oxide), which burns with a blue flame.
Q. Why is the flame of a good fire yellow?
A. Because both the hydrogen and carbon of the fuel are in a state of perfect combustion. It is the white heat of the carbon, which gives the pale yellow tinge to the flaming hydrogen.
Q. What is light?
A. Rapid undulations of a fluid called ether, striking on the eye.
Q. How does combustion make these undulations of light?
A. The atoms of matter (set in motion by heat) striking against this ether, produce undulations in it; as a stone thrown into a stream, would produce undulations in the water.
Q. How can undulations of ether produce light?
A. As sound is produced by undulations of air striking on the ear; so light is produced by undulations of ether striking on the eye.
Q. What is ether?
A. A very subtile fluid, which pervades and surrounds every thing we see.
Q. Mention a simple experiment to prove that light is produced by rapid motion.
A. When a fiddle-string is jerked suddenly, its rapid vibration produces a grey light; and when a carriage wheel revolves very quickly, it sends forth a similar light.
Q. Does heat always produce light?
A. No: the heat of a stack of hay, or reeking dunghill, though very great, is not sufficient to produce light.
Q. Why is a yellow flame brighter than a red hot coal?
A. Because yellow rays always produce the greatest amount of light; though red rays produce the greatest amount of heat.
Q. Why is the light of a fire more intense sometimes than at others?
