CHAPTER V.. Lamps and Candles.

LAMPS AND CANDLES.

Q. Of what are OIL, TALLOW, and WAX composed?

A. Principally of carbon and hydrogen gas. The solid part is carbon, the volatile part is gas.

Q. What is CARBON?

A. A solid substance, generally of a black colour; well known under the forms of charcoal, lamp-black, coke, black-lead, &c.

Q. What is HYDROGEN GAS?

A. The principal ingredient of water. It is well known in the form of common coal gas: it burns so readily that it used to be called "inflammable air."

To make hydrogen gas, see p. 34.

Q. Why does a CANDLE BURN when lighted?

A. The heat of the lighted wick decomposes the tallow into its elementary parts of carbon and hydrogen; and the hydrogen of the tallow, combining with the oxygen of the air, produces flame.

Q. Why is the FLAME of a candle HOT?

A. 1st--Because the flame liberates latent heat from the air and tallow: and

2ndly--It throws into rapid motion the atoms of matter.

Q. How is LATENT HEAT liberated by the flame of a CANDLE?

A. When the hydrogen of the tallow and oxygen of the air combine, they condense into water; and much of their latent heat is squeezed out.

Q. How are the ATOMS of MATTER disturbed by the flame of a candle?

A. 1st--When the hydrogen of the tallow and oxygen of the 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.

2ndly--When the carbon of tallow and oxygen of the air expand into carbonic acid gas, the air is again disturbed; in a similar way as by the explosion of gunpowder.

Q. Why does the flame of a CANDLE produce LIGHT?

A. The chemical changes made by combustion, excite undulations of ether, which (striking the eye) produce light. (see p. 46.)

Q. Why is the FLAME of a CANDLE YELLOW?

A. Only the outer coat of the flame is yellow; the lower part of the flame is violet; and the inside of the flame is hollow.

Q. Why is the outside of the flame YELLOW?

A. Because the carbon of the tallow (being in a state of perfect combustion) is made white-hot.

Q. Why is the BOTTOM part PURPLE of the flame of a candle?

A. The bottom part of the flame is overladen with hydrogen, raised from the tallow by the burning wick; and this half-burnt gas gives a purple tinge to the flame.

Q. Why is the INSIDE of the flame of a candle HOLLOW?

A. Because it is filled with vapour, raised from the candle by the heat of the wick.

Q. Describe the different parts of the FLAME of a common CANDLE.

A. The flame consists of three cones. The innermost cone is hollow; the intermediate cone of a dingy purple hue; and the outside cone is yellow.

Q. Why is the intermediate cone of a flame PURPLE, as well as the BOTTOM of the flame.

A. Because the gases are not in a state of perfect combustion; but contain an excess of hydrogen, which gives this cone a purple tinge.

Q. Why is not the MIDDLE cone in a state of perfect combustion, as well as the OUTER cone?

A. Because the outer cone prevents the oxygen of the air from getting freely to the middle of the cone; and without the free access of oxygen gas, there is no such thing as complete combustion.

Q. Why does the FLAME of a candle point UPWARDS?

A. The flame heats the surrounding air, which (being hot) rapidly ascends, and drives the flame upwards at the same time.

Q. Why is the FLAME of a candle POINTED at the top, like a cone?

A. The upper part of a flame is more volatile than the lower parts; and as it affords less resistance to the air, is reduced to a mere point.

Q. Why is the UPPER part of a flame more VOLATILE than the lower parts?

A. The lower parts of the flame are laden with unconsumed gas and watery vapour; which present considerable resistance to the air.

Q. Why is the FLAME of a candle BLOWN OUT by a puff of breath?

A. As the flame of a candle is attached to a very small wick, a puff of breath severs the flame from the wick; and it goes out for want of support.

Q. Why does the FLAME of a candle make a GLASS DAMP, which is held over it?

A. The hydrogen of the tallow combining with the oxygen of the air, produce a "watery vapour," which is condensed by the cold glass held above the flame.

Q. Why does our hand, held ABOVE a candle, suffer from the heat of the flame so much more, than when it is placed BELOW the flame, or on ONE SIDE of it?

A. Because the hot gases and air (in their ascent) come in contact with the hand placed above the flame: but when the hand is placed below the flame, or on one side, it only feels heat from radiation.

Q. Why is a RUSH LIGHT extinguished so much more quickly than a cotton-wicked candle?

A. As the rush wick is smooth and hard, the mere motion of the air (produced by carrying the candle from one place to another,) is sufficient to sever the flame from the rush.

Q. Why is it more difficult to blow out a COTTON wick?

A. The cotton wick is quite full of small threads or filaments, which help to hold the flame on the wick, like the roots of a tree.

Q. Why does an EXTINGUISHER put a candle out?

A. Because the air in the extinguisher is soon exhausted of its oxygen by the flame: and when there is no oxygen to support it, the flame goes out.

Q. Why does not a candle set fire to a PIECE OF PAPER twisted into an extinguisher, and used as such?

A. 1st--Because the flame very soon exhausts the little oxygen contained in the paper extinguisher: and

2ndly--The flame invests the inside of the paper extinguisher with carbonic acid gas, which prevents it from blazing.

Q. Why is a LONG WICK never upright?

A. Because it is bent by its own weight.

Q. Why is a LONG WICK covered with an EFFLORESCENCE at the top?

A. The knotty or flowery appearance of the top of a wick arises from an accumulation of particles partly separated, but still loosely hanging to the wick.

Q. Why is not the END of a long wick BURNT OFF, as it hangs over the flames?

A. Because the length of the wick so diminishes the heat of the flame, that it is not hot enough to burn it off.

Q. Why do PALMER'S METALLIC WICKS never need SNUFFING?

A. The wick is divided into two parts, each of which bends outward to the outside of the flame; where the end is intensely heated, and separated from the wick by the current of air up the candle.

Q. Why do common CANDLES require to be SNUFFED?

A. Because the heat of the flame is not sufficient to consume the wick; and the longer the wick grows, the less heat the flame produces.

Q. Why do WAX CANDLES NEVER need SNUFFING?

A. The wick of wax candles is made of very fine thread, which the heat of the flame is sufficient to consume: but the wick of tallow candles is made of coarse cotton, which is too substantial to be consumed by the heat of the flame, and must be cut off by snuffers.

Q. Why does a PIN, stuck in a RUSH-LIGHT, EXTINGUISH it?

A. Because a pin (being a good conductor), carries away the heat of the flame from the wick, and prevents the combustion of the tallow.

Q. What is the SMOKE of a CANDLE?

A. Solid particles of carbon separated from the wick and tallow, but not consumed.

Q. Why are SOME particles consumed and not OTHERS?

A. The combustion of the carbon depends upon its combining with the oxygen of the air: but as the outer surface of the flame prevents the access of air to the interior parts, therefore much of the carbon of those parts passes off in smoke.

Q. Why do LAMPS SMOKE?

A. Either because the wick is cut unevenly, or else because it is turned up too high.

Q. Why does a LAMP SMOKE when the WICK is cut UNEVENLY?

A. 1st--Because the points of the jagged edge (being very easily separated from the wick,) load the flame with more carbon than it can consume: and

2ndly--As the heat of the flame is greatly diminished by these bits of wick, it is unable to consume even the usual quantity of smoke.

Q. Why does a LAMP SMOKE when the WICK is turned up too HIGH?

A. Because more carbon is separated from the wick than can be consumed by the flame.

Q. Why do not "Argand burners" smoke?

A. Because a current of air passes through the middle of the flame; and therefore the carbon of the interior is consumed, as well as that in the outer coating of the flame.

Q. Why does a LAMP-GLASS DIMINISH the SMOKE of a lamp?

A. Because it both concentrates and reflects the heat of the flame; in consequence of which, the heat is so greatly increased, that very little carbon escapes unconsumed.