KINDLING AND CARE OF FIRES To Kindle Fires.—Suggestions for kindling fires must naturally be modi fied according to circumstances. There is a vast difference between the elec tric range that, by pulling a lever, can be instantly adjusted at any given temperature, the gas range that re quires merely the scratch of a match, the coal or wood kitchen range, the fireplace, and the furnace.
The principles of combustion, how ever, are identical in all cases, and a proper understanding of these will en able anyone to build a good fire as quickly as may be under all circum stances. Combustion consists in the union of the oxygen of the air with va rious substances, and this takes place at different temperatures according to the substances burned. Phosphorus has so strong an affinity for oxygen that, if exposed to the air, it will burn instantly. Hence pure phosphorus must be kept under water, and when used in making matches is mixed with other materials to prevent too speedy combustion. Sulphur kindles at a somewhat higher temperature than phosphorus, pine or other soft woods at still higher temperatures, and so on with charcoal, coke, hard wood, coal, and various other kinds of fuel. Hence two things are necessary to kindle a fire: a draught of air to sup ply plenty of oxygen, and heat enough to cause the oxygen to unite freely with the kind of fuel used.
All substances may exist in three forms, as gases, liquids, or solids—as in the case of steam, water, and ice— and of these three forms, since the oxygen of the air can penetrate quick ly to every part of it, the easiest to kindle is gas.
Heat decomposes solid substances and liquids, and causes them first to melt and afterwards to turn into gas, or, in the case of compounds, into various gases, or in some cases to im mediately throw off various gases without the preliminary stage of melt ing. The flames that rise from the sur face of fuel are caused by the gases thrown off in the process of combus tion. Hence, when heat enough is supplied to cause fuel to decompose into various gases, these may be read ily kindled, and those forms of fuel that throw off inflammable gases at the lowest temperatures are most suit able for kindling. Kerosene oil, for
example, at ordinary temperatures will put out a match as readily as water, but at about 110° to 125° F. it com mences to throw off a volatile and in flammable gas, and at a still higher temperature it may be instantly trans formed into gas by means of what we call an explosion.
The difficulties to be overcome in kindling a fire are to raise the mass of fuel to a sufficiently high tempera ture, so that inflammable gases will be released and kindled; also to shield the fuel from the surrounding atmos phere (which tends to cool it), and at the same time to furnish, by means of a draught, a sufficient supply of oxy gen to promote combustion.
Wet or green wood, especially hard wood in large, solid chunks, and soft or hard coal in large lumps, are diffi cult to kindle, because they are very cold, and because only a comparatively small surface is exposed to the action of heat from materials used as kin dlings. It is quite common to notice in building fires that large chunks of coal or wood become kindled and burn for a time, but afterwards go out. This is because the heat of the kin dlings warms the surface of the chunks enough to drive off the inflam mable gases in small quantities, but is not sufficient to warm the re mainder to a point where the oxygen could combine and continue the com bustion. Indeed, the charred or par tially burned surface may shield the heart of the chunk by preventing the oxygen from reaching it. Hence, to make combustion possible, there must be sufficient heat to cause the entire chunk to throw off inflammable gases.
Another difficulty is to admit enough air to supply the oxygen necessary to combustion, but not enough to put out the fire by lowering its temperature. The difficulty of kindling a fire in a grate is due to the fact that the con tact of air above and around the fuel, which is not and cannot be consumed in the process of combustion, tends to cool it and thus to retard combus tion. Hence a draught should pass through the fire from beneath, and be regulated in such a way that no more air will be admitted than is required.