Wax candles cannot be cast as tallow are. To make them, a number of cottons are hung on frames, and covered with metal tags at the ends to keep the wax from covering the cotton. Melted wax is then poured, by a man, over them; the frame being brought close to the wax-heater. When the first wax is cold a second coat is given, and so on till the candles are as thick as they are required to be. When finished, they are taken down and well rolled upon a fine stone slab; the conical top is moulded by properly-shaped tubes, and the bottoms cut off and trimmed. The wicks of tallow candles require snuffing because they are never quite consumed in the flame, the outer cone preventing a sufficient supply of oxygen reaching it for complete combustion. Wax and composite candles do not require snuffing, because the wick is so plaited as to bend into the outer cone of the flame where it is completely consumed. This cannot be done with tallow candles, because this bending of the wick into the outer cone would melt the tallow on one side too quickly, and cause the candle to gutter; tallow melting at a much lower temperature than wax or stearine.

The continuous flame of the candle is caused by the heated wick decomposing the wax or tallow, and forming vapour of water and carbonic acid gas. The hydrogen of the candle combining with the oxygen of the air forms the former; the carbon of the candle combining with the oxygen forms the carbonic acid gas.

As the air comes to the candle, it moves upwards by the force of the current which the heat of the candle produces, and cools all the sides of the wax or tallow, so that it keeps the edges much cooler than the part within; the part within is heated by the flame which runs down the wick as far as it can go before it is extinguished, and forms a little cup of liquid tallow or wax, while the edges never melt. Of course, if by leaning the candle on one side, a current of air is made in a slanting direction, the cup will become lopsided and the fluid will run over, or gutter, as it is called.

The horizontal formation of this cup is of the first importance, for if it be not horizontal the fluid will run away in guttering.

Fluted candles are not good for burning on this account; they have not the nicely formed edge to the cup, which is the perfection of a candle, and consequently prove wasteful from guttering.*

The fuel for the flame is this melted part of the candle which is carried up the wick by capillary attraction - which we have already explained in a note at p. 59. Capillary attraction is sometimes unpleasantly but well exemplified by some careless person leaving the corner of a towel in water - the water, by the power of capillary attraction, spreads all over the towel and wets it through. In the like manner, water rises through a sponge, or a lump of sugar. Thus the melted tallow ascends the wick; other particles follow from their mutual attraction to each other, and arc gradually consumed. Whenever the flame descends into the melted tallow it is instantly extinguished, therefore the flame remains in the place where we always see it.

The flame of a candle consists of three cones; the inner or hollow cone, in which no combustion takes place, and which is filled with invisible vapour raised from the candle by the heat of the wick, and which cannot burn because it does not come in contact with the outer air; an intermediate cone, where hydrogen is chiefly consumed with particles of carbon which it raises to a white heat (from thence the light chiefly proceeds); and the outer cone in which the carbon is consumed. The flame of a candle produces light because the chemical changes made by combustion excite undulations of luminous ether which, striking the eye, produce light. The light of the flame is yellow, because that is the colour of carburetted hydrogen when burning; and here we may observe that yellow rays produce the greatest amount of light, as red rays produce the greatest amount of heat.

The flame of a candle is of an oblong shape, brighter at the top than towards the bottom; it is carried upwards by the ascending air, which, heated by the candle, goes rapidly upwards. The darker parts, towards the bottom of the flame, are particles of the fuel not in a perfect state of ignition.

Certain products result from the combustion of a candle. One of these products is charcoal, or soot. Some of our readers may have seen etchings done on a card rapidly passed through, or over a lighted candle, till it is shaded black, or dark brown, with soot. But, if the candle burns well, that is, if the combustion is perfect, no smoke or soot will proceed from it; soot being, as we have said, the escape of unconsumed fuel.

Water also is produced from the flame of a candle - i.e., vapour of water which, if cooled, will condense as water. Water is likewise produced from the combustion of gas and from that of oil - a pint of oil fairly and properly burned produces rather more than a pint of water. In fact, all combustible substances which burn with a flame produce vapour of water, which may be condensed if anything cold enough is held over it.

The combustion of a candle also produces, as we have said, carbonic acid gas, very often called fixed air,* and evolves heat from it precisely as we by breathing make heated carbonic acid gas, and thus feed the animal heat. The candle cannot burn without oxygen; neither can we live without oxygen, as we have before observed.

* The action of the ascending current of air on the outside of a candle may be seen when it has guttered. The thickened piece at the side forms a little pillar, as the candle goes on burning, because as it rises higher above the rest of the tallow or wax, the air gets better round it and it is more cooled.

A lamp burns on the same principle as a candle, and is probably long prior to it in antiquity.

The oil is the fuel which, by capillary attraction, ascends the wick and is consumed by the carbon combining with the oxygen of the air. The Argand lamp is remarkable for its excellent combustion. A current of air is made to pass through the middle of the flame, in consequence of" which the carbon of the interior of the flame is consumed as well as that in the outer coating. These lamps do not smoke, because the combustion is perfect. Lamp-glasses diminish the smoke from lamps by producing a draught, which supplies more oxygen to the flame; they also concentrate and reflect the heat of the flame, thus helping its combustion.

Lamps smoke, either because the wick is turned up too high and more carbon is separated from it than can be consumed by the flame, or from the wick having been cut unevenly. When this is the case, the points of the jagged edge project into the flame where there is not enough oxygen to consume the carbon and, of course, cause smoke.

Candles and lamps will often spirt when rain is at hand. This is caused by the air being filled with vapour which penetrates the wick, where, being formed into steam, it expands suddenly, and produces a little explosion.

We cannot conclude these few remarks about the combustion of carbon without adding to them a passage from Professor Faraday's admirable lectures on the "Chemical History of a Candle," which we recommend to the perusal of our readers. He is speaking of the creation of carbonic acid gas: -

"You will be astonished when I tell you what this curious play of carbon amounts to. A candle will burn some four, five, six, or seven hours. What then must be the daily amount of carbon going up into the air in the way of carbonic acid? What a quantity of carbon must go from each of us in respiration? A man, in twenty-four hours, converts as much as seven ounces of carbon into carbonic acid; a milch cow will convert seventy ounces, and a horse seventy-nine ounces, solely by the act of respiration; that is, the horse in twenty-four hours burns seventy-nine ounces of charcoal, or carbon, in his organs of respiration to supply his natural warmth in that time. All the warm-blooded animals get their warmth in this way, by the conversion of carbon, not in a free state, but in a state of combination. And what an extraordinary notion this gives us of the alterations going on in our atmosphere. As much as 5,000,000 pounds, or 548 tons of carbonic acid is formed by respiration in London alone in twenty-four hours. And where does all this go? Up into the air. If the carbon had been like the lead which I showed you, or the iron which, in burning, produces a solid substance, what would happen? Combustion could not go on.

As charcoal arises it becomes a vapour and passes off into the atmosphere which is the great vehicle, the great carrier for conveying it away to other places. Then what becomes of it? Wonderful it is to find that the change produced by respiration, which seems so injurious to us (for we cannot breathe air twice over), is the very life and support of plants and vegetables that grow upon the surface of the earth. It is the same also under the surface in the great bodies of water; for fishes respire upon the same principle, though not exactly by contact with the open air."*

* It was so called by Dr. Black because it is found fixed in chalks, shells, corals, and all limestones. Marble is a compound of carbonic acid and lime.