Coke is manufactured from coal, and may be produced in two ways: It may be a by-product of the distillation of coal for the production of tar, ammonia, etc., or it may be obtained by heating the coal in a coke oven with an almost entire exclusion of air. It has a dull appearance, and gives a metallic ring when struck. That made in the oven or kiln of brick or stone is the best quality of coke, and is used for melting pig iron, and for smelting copper and lead. Coke was formerly made by a method similar to that used in the manufacture of vegetable charcoal. Much of the coke found in fuel markets is that produced as a by-product in the manufacture of gas. This is not equal to the best oven coke, but is a reasonably good heat producer, and is much more cleanly than bituminous coal. No special stove or furnace is needed for burning it. It burns out grates and fixtures more than other fuels. Coke, like charcoal, needs to be stored in a dry place, as its porous nature causes it to absorb much moisture, and this interferes very materially with its value as a fuel.
Charcoal bears the same relation to wood as coke does to coal. The manufacture of coke and charcoal are both processes of destructive distillation. Usually means are employed to save the useful materials which are driven off by the heat.
Charcoal makes an excellent fire for broiling meats, as it, like the coke, burns with a bluish flame, without smoke, deposits no soot, and yields an intense heat. Charcoal can be very economically used for a broiling fire in the range when there is no fire needed for other things. When through using the coal, extinguish it with water, and when thoroughly dried it will burn equally well.
Wood is more universally used as a fuel than coal, oil, and gas. In many cases it is cheaper than hard coal, and cleaner than soft coal. Gas is a pleasant fuel for cooking purposes, but is not generally available, and is expensive in some localities. Wood, to be most valuable as a fuel, must be dense and dry. Green wood contains much moisture, and it is not possible to have so hot a fire quickly with it. As this is often needed in the kitchen, it is better to avoid green wood, because some heat must be used up in vaporizing the water in the wood. The amount of water varies, but forms from one-fifth to one-half the weight of the wood. The essential elements of wood are carbon, hydrogen, and oxygen. There is mineral matter present, also, as is shown by the ash after the wood is burned.
Wood for fuel purposes may be divided into hard and soft woods. The same rule holds good in wood as in coal in this respect, - the hard fuel is the best. Hard wood, such as oak or hickory, gives a nice bed of glowing coals, which continue to yield heat long after the blaze is gone.
When a steady fire is required for baking, a few sticks of hard wood of good size will make it possible to control the heat during a long period of time. Soft wood burns to ashes very quickly, gives a good heat, but needs constant watching and replenishing.
In order to have wood serve its purpose best in the kitchen range, it must be cut long enough before using to give it time to become thoroughly dried out or seasoned. Trees for fuel should not be cut when they are what the woodmen call "in sap"; that is, when they are in leaf, or after the buds begin to swell in the spring. Such wood is more apt to be infested by insects, and decay sets in sooner.
Wood when ready for the stove should be short enough to be admitted readily, but not so short as to pack the fire. When seasoned and cut, it should be packed in a dry place. Moisture from rain dries out more quickly than the natural moisture from the tree, but decreases the value of the fuel, and annoys the housekeeper as well. The wood itself burns better than the bark, and produces less ashes.
In buying wood, avoid that which has many crooked or knotty sticks. It will not lie close, and what is gained in the resinous knots of the soft wood will hardly compensate for what is lost in measure. The absence of bark, or the shelling off of the bark, is an indication that the wood has passed its best stage, and begun to deteriorate slightly. Soft wood is better than hard wood for kindling, because more easily manipulated, and it also burns more readily.