Heat is molecular motion, and is produced by combustion. Heat used for cookery is obtained by the combustion of inflammable substances— wood, coal, charcoal, coke, gas, gasoline, kerosene, and alcohol— called fuels. Heat for cookery is applied by radiation, conduction, and convection.

Air is composed of oxygen, nitrogen, and argon, and surrounds everything. Combustion cannot take place without it, the oxygen of the air being the only supporter of combustion.

Moisture, in the form of water, either found in the food or added to it.

The combined effect of heat and moisture swells and bursts starch-grains; hardens albumen in eggs, fish, and meat; softens fibrous portions of meat, and cellulose of vegetables.

Among fuels, kerosene oil is the cheapest; gas gives the greatest amount of heat in the shortest time. Soft wood, like pine, on account of its coarse fibre, burns quickly; therefore makes the best kindling. Hard wood, like oak and ash, having the fibres closely packed, burns slowly, and is used in addition to pine wood for kindling coal. Where only wood is used as a fuel, it is principally hard wood.

Charcoal for fuel is produced by the smothered combustion of wood. It gives an intense, even heat; therefore makes a good broiling fire. Its use for kindling is not infrequent.

There are two kinds of coal: Anthracite, or hard coal. Examples: Hard and free-burning White Ash, Shamokin, and Franklin. Nut is any kind of hard coal obtained from screenings. Bituminous, or soft coal. Example: Cannel coal.

Coke is the solid product of carbonized coal, and bears the same relation to coal that charcoal bears to wood.

Alcohol is employed as fuel when the chafing-dish is used.