A Guide to the Scientific Knowledge of Things Familiar. Ebenezer Cobham Brewer
ingredient of the common air.[9]
[9] Nitrogen gas may easily be obtained thus:—Put a piece of burning phosphorus on a little stand, in a plate of water; and cover a bell glass over. (Be sure the edge of the glass stands in the water.) In a few minutes the air will be decomposed, and nitrogen alone remain in the bell glass.
(N.B. The white fume which will arise and be absorbed by the water in this experiment, is phosphoric acid; i.e. phosphorus combined with oxygen of the air.)
Q. Why is there so much nitrogen in the air?
A. In order to dilute the oxygen. If the oxygen were not thus diluted, fires would burn out, and life would be exhausted too quickly.
Q. What three elements are necessary to produce combustion?
A. Hydrogen gas, carbon, and oxygen gas; the two former in the fuel, and the last in the air which surrounds the fuel.
Q. What causes the combustion of the fuel?
A. The hydrogen gas of the fuel being set free, and excited by a piece of lighted paper, instantly unites with the oxygen of the air, and makes a yellow flame: this flame heats the carbon of the fuel, which also unites with the oxygen of the air, and produces carbonic acid gas.
Q. What is carbonic acid gas?
A. Only carbon (or charcoal) combined with oxygen gas.
Q. Why does fire produce heat?
A. 1st—By liberating latent heat from the air and fuel: and
2ndly—By throwing into rapid motion the atoms of matter.
Q. How is latent heat liberated by combustion?
A. When the oxygen of the air combines with the hydrogen of the fuel, the two gases condense into water; and latent heat is squeezed out, as water from a sponge.
Q. How are the atoms of matter disturbed by combustion?
A. 1st—When hydrogen of fuel and oxygen of air condense into water, a vacuum is made; and the air is disturbed, as a pond would be, if a pail of water were taken out of it: and
2ndly—When the carbon of fuel and oxygen of air expand into carbonic acid gas, the air is again disturbed, as it would be by the explosion of gunpowder.
Q. How does fire condense hydrogen and oxygen into water?
A. The hydrogen of fuel and oxygen of air (liberated by combustion) combining together, condense into water.
Q. How does fire expand carbon into carbonic acid gas?
A. The carbon of fuel and oxygen of air (combining together in combustion) expand into a gas, called carbonic acid.
Q. Why is a fire (after it has been long burning) red hot?
A. When coals are heated throughout, the carbon is so completely mixed with the oxygen of the air, that the whole surface is in a state of combustion, and therefore red hot.
Q. In a blazing fire, why is the upper surface of the coals black, and the lower surface red?
A. Carbon (being very solid) requires a great degree of heat to make it unite with the oxygen of the air. When fresh coals are put on, their under surface is heated before the upper surface; and one is red (or in a state of combustion), while the other is black.
Q. Which burns the quicker, a blazing fire, or a red hot one?
A. A blazing fire burns out the fuel quickest.
Q. Why do blazing coals burn quicker than red hot ones?
A. In red hot coals, only the mere surface is in a state of combustion, because the carbon is solid; but in a blazing fire, (where the gases are escaping), the whole volume of the coal throughout is in a state of decomposition.
Q. What is smoke?
A. Unconsumed parts of fuel (principally carbon), separated from the solid mass, and carried up the chimney by the current of hot air.
Q. Why is there more smoke when coals are fresh added, than when they are red hot?
A. Carbon (being solid), requires a great degree of heat to make it unite with oxygen, (or, in other words, to bring it into a state of perfect combustion): when coals are fresh laid on, more carbon is separated than can be reduced to combustion; and so it flies off in smoke.
Q. Why is there so little smoke with a red hot fire?
A. When a fire is red hot, the entire surface of the coals is in a state of combustion; so a very little flies off unconsumed, as smoke.
Q. Why are there dark and bright spots in a clear cinder fire?
A. Because the intensity of the combustion is greater in some parts of the fire, than it is in others.
Q. Why is the intensity of the combustion so unequal?
A. Because the air flies to the fire in various and unequal currents.
Q. Why do we see all sorts of grotesque figures in hot coals?
A. Because the intensity of combustion is so unequal, (owing to the gusty manner in which the air flies to the fuel; and the various shades of red, yellow, and white heat mingling with the black of the unburnt coal), produce strange and fanciful resemblances.
Q. Why does paper burn more readily than wood?
A. Merely because it is of a more fragile texture; and, therefore, its component parts are more easily heated.
Q. Why does wood burn more readily than coal?
A. Because it is not so solid; and, therefore, its elemental parts are more easily separated, and made hot.
Q. When a fire is lighted, why is paper laid at the bottom, against the grate?
A. Because paper (in consequence of its fragile texture), so very readily catches fire.
Q. Why is wood laid on the top of the paper?
A. Because wood, (being more substantial), burns longer than paper; and, therefore, affords a longer contact of flame to heat the coals.
Q. Why would not paper do without wood?
A. Because paper burns out so rapidly, that it would not afford sufficient contact of flame to heat the coals to combustion.
Q. Why would not wood do without shavings, straw, or paper?
A. Because wood is too substantial to be heated into combustion, by the flame issuing from a mere match.
Q. Why would not the paper do as well, if placed on the top of the coals?
A. As every blaze tends upwards, if the paper were 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;