Domestic science (Clark, Cornell home economics)

Combustion. A flame bums more brightly when there is a strong current of air. This may be seen by comparing the flames of two candles, one burning in air, the other arranged with an inlet and outlet for the air draft. The direction of the draft is upward. In a lamp, air enters at the bottom and goes out at the top of the chimney. To see this, hold tissuepaper above the chimney and near the space at the base of chimney. If there is no inlet for air, the flame will soon go out for lack of oxygen. If the outlet is shut, there will be no draft, and the flame will be extinguished. The oxygen in the air is necessary to support combustion. A lighted match will go out in air from which oxygen is absent. The fire in the stove is in many ways similar to the flame in a lamp. Stoves are comparatively recent household conveniences. Long before stoves were known, people cooked before an open fire or buried their food in hot ashes. The stove and the things necessary to it came only gradually into use. The essential parts of the stove are the fire-box, grate, ash-pan, oven and pipe. Laying a Fire. To build a fire it is necessary to have fuel — paper, wood, coke or coal — and the match with which to ignite it. The fuel is placed in the order given, paper first, so that the fuel most easily ignited is nearest the inlet of air, and the draft passes up through the other fuel. Nothing can bum without heat. Some substances require more heat to ignite them than others. The match is a piece of wood with sulphur or phosphorus at the end. Sulphur and phosphorus cannot burn when cool. The heat which starts the flame of the match is produced by the mbbing or striking of the match against a rough surface. The friction raises the temperature of the sulphur or phosphorus and produces combustion. Coal could not be used at the end of a match because it does not bum at a low temperature. Friction is not sufficient to set wood on fire and for this reason sulphur, which ignites easily, is used. The sulphur flame produces enough heat to ignite the wood of the match, that is, to raise it to the temperature at which it burns. Matches are not sufficient to raise a large amount of wood to the temperature required for combustion, so we use paper as a medium to bring that about. the wood in turn heats the coke and coal to the temperature at which it ignites, and the fire in the range is the result. Since air is necessary for combustion, and burning ceases when the air is shut off, it is necessary to furnish a supply of air to support a fire. The dampers regulate the air supply and draft. The air enters at the bottom, passes through and over the fire and out at the chimney. Paper and wood for the fire must be so arranged as to allow a free passage of air through them and thus reach the fuel above. For this reason the paper should not be left folded but should be crumpled, and the wood and coal arranged loosely so as not to stifle the fire at the start. COMBUSTION, FUELS AND FIRES 203 The fire at first must have encouragement, and the dampers should be wide open to allow the air to go up the chimney. The oven damper checks the draft and therefore should be open until a brisk fire is going. If it is then desired to use the oven, the circulation must be checked and the hot air turned over the oven by closing or partly closing the oven damper. The damper in the pipe should likewise be open when the fire is starting. If there is a free circulation after the fire is well started, the fire will not last long. It must then be checked by closing some of the dampers. This checks the fire by reducing the supply of air and decreasing combustion. The fire should not be checked until a good bed of coal is well started. All the coal for the fire should not be put on until a first layer of it is started; then more can be added.