This section is from the book "Elements Of The Theory And Practice Of Cookery", by Mary E. Williams. Also available from Amazon: Elements Of The Theory And Practice Of Cookery; A Textbook Of Domestic Science For Use In Schools.
Anything that unites readily with oxygen may be used as fuel. Fuels common in American households are coal, wood, coal-oil (kerosene), and gas.
Coal, by composition and structure, is shown to be of plant origin. Leaves, ferns, bark, whole tree trunks even, have been found turned to coal in mines. The slow process of decay that effected this change took place long before men lived on the earth, at a time when the land was covered with thick forests different from any growing now. Many trees then resembled gigantic ferns. Evidently these forests were flooded from time to time, the trees being overthrown and buried beneath sand washed in by the water. The flood subsiding, a new forest arose, to be in turn similarly buried. Pressure, combined with heat greater than now prevails anywhere on earth, slowly destroyed everything in these layers of plant-substance except the carbon, and left them as seams of coal.
1 There should be no key in connecting pipe which can be turned by hand. If there is, it should not be used instead of turning cock to shut off gas from stove, because an open cock may be overlooked, and when the gas is again turned on it will escape from this cock. In this way, gas may accumulate in the oven and explode.
The heat of burning coal may be utilized to cook food, melt iron, make steam to drive engines, and do hundreds of other kinds of work. A person able to work is said to have energy. Whence comes the energy of coal ? From its carbon. But the carbon in the plants the coal was made from was stored up by the help of the sun. Plants obtain carbon from the carbon dioxide in the air. They can do this only in the light.
The sun, then, is the source of the energy in coal; we may say that the sun lights our fires. Stephenson, the inventor of the locomotive, when asked what drove his engine, answered, "Bottled-up sunshine." He spoke the exact truth; the sun's energy is stored up in coal-mines until, with pick and blasting powder, man sets it free.
Hard, or anthracite, coal is the result of almost perfect carbonization of wood; in soft, or bituminous, coal the carbonizing has not gone so far.1
1 Wood contains about 50% of carbon, bituminous coal about 77%, anthracite about 90 %. All coal contains sulphur. Charcoal is wood carbonized by burning it with just enough air to char it, but not consume it.
The latter is crumbly and dull, and burns with much smoke. Which yields the more heat; i.e., has the more energy, hard or soft coal? Hard coal is best for household use, but as it is mined chiefly in the Atlantic states, in many parts of the country it is too expensive to be used. A good quality is jet black and glossy, breaks into roughly cube-shaped pieces, is free from slate, and yields little clinker. For a stove with a small fire-box, use chestnut coal; for most ranges a mixture of stove and chestnut is desirable. Too small coal will fall between the bars of the grate before being burned. It is prudent to buy a year's supply of coal in summer, when it is cheapest; coal bought by the pound or basket costs about three times as much as if bought by the ton.
Coal burns at first with a blue flame, but when thoroughly afire, with a clear, red glow. When white-hot, almost all its heat-giving power has been exhausted. A good coal fire consists of a mass of red coals covered by a layer of black ones heating and ready to kindle when the red ones die out. More heat is obtained from the same quantity of coal by adding it to the fire a little at a time than by putting it on all at once.
By the first method the coal gets sufficient air to be burned to carbon dioxide (C02); by the second, much of it is burned to carbon monoxide (CO). Thus it takes up only half as much oxygen as it is capable of uniting with, and so produces less heat.
Kerosene, or coal-oil, prepared from the mineral oil petroleum, is the cheapest household fuel, and is safe when it is of good quality and is burned in stoves intended for it. Never use kerosene to kindle a wood or coal fire. When heated, it gives off vapor that in contact with fire is likely to explode.
Natural gas, used for heating and lighting, flows from the ground. Both it and coal-oil are believed to be of vegetable origin. What is the source of their energy? Two kinds of gas are manufactured for lighting and heating purposes. Coal-gas is made by heating soft coal in a closed retort. Water-gas is made by passing steam over white-hot coke or anthracite coal.
A soft coal fire needs little draft below, but some on top to carry off the smoke and gas. It must be fed often and is hard to keep overnight. Some soft coal cokes as it burns. Break up the crust to keep the draft free.
Wood burns best with a wider grate than is needed for coal. It gives a quick heat, but more wood must be added often to keep the heat steady.
Distillate oil, used in the southwest where wood and coal are scarce, is a heavy coal-oil. The distillate burner fits into the fire-box of any range. It gives intense heat and is safe.