Figure 13 shows the three dials found on the face of a gas meter. The arrows show the direction. The dial at the right indicates 100 cubic feet between the numbers, the middle dial 1000 and the left hand dial 10,000. The dials in this figure record 53,250 cubic feet. The price of gas varies from eighty cents to a dollar and a half per thousand cubic feet. "Eighty-cent gas" is the hope of many a consumer. At a dollar and a half it is not a cheap fuel.
Gas does away with the handling of coal and ashes in the kitchen and is thus a clean and labor-saving fuel. It gives an intense heat the moment the flame is lighted and this heat is easily regulated in a well-made stove. The flame should burn with a clear blue or greenish color. With a properly constructed stove only a small percentage of the heat is lost. In all these points it has the advantage over coal. The comparative cost is studied in the problems on page 53.
Natural gas is used in those regions where it occurs, piped to the house from a central source. It is found in limited areas only, and in some places has already been exhausted.
Coal oil, or petroleum, sometimes found oozing from crevices in rocks, or even floating on water, is a natural inflammable oil stored in the earth. It was known in ancient Persia, Greece, and Rome, but did not become of great commercial importance until the middle of the nineteenth century. It is now obtained by boring wells, and is found in great quantities in certain regions of the country. The crude oil yields many products valuable in the arts, medicine, and manufacture. Kerosene is the substance useful as a fuel and for giving light. When of good quality it is nearly colorless, and the flashing point should be 149° F., or 65° C. This flashing point is the temperature at which the vapor from the kerosene explodes or flashes. If the vapor flashes at a point lower than this, it means that the oil has not been sufficiently refined; that is, in the process of manufacture the substances that flash at a low temperature have not been removed, and therefore the oil is less safe.
Kerosene is sold by the gallon or barrel. The price for a good quality is about seventy cents for a five-gallon can. By the barrel a saving is made of several cents a gallon. It is useful as a fuel to those housekeepers who cannot have gas, and who find it a convenient substitute for coal in the summer. With the new blue flame stoves it gives an intense heat, easily regulated. There is no heavy labor involved in its use, but even the best stove requires constant care and watchfulness. It is not so clean and easy to use as gas. The kerosene supply should be kept in a cool place, and stoves and lamps should never be filled by candle or lamplight.
Gasolene is used as a fuel for cooking in some places, but in others the fire insurance companies have such strict rules in regard to it that its use is practically prohibited. It is more volatile than kerosene, and its flashing point is very low. Kerosene is much safer for household use.
Alcohol is used with the chafing dish. Denatured alcohol is so cheap in Germany that it is used in large and especially adapted stoves for cooking purposes. There are denatured alcohol stoves on the market here, but they are little used.
Charcoal, wood partially burnt out, is little used for domestic purposes now.
The relative value of the common fuels is stated in quantities as follows, but this is of course dependent on the quality of the coal and the gas. One thousand feet of gas about equals from fifty to sixty pounds of coal, or four and one half gallons of kerosene; and one half ton of coal approximates a cord of wood.
Those who may be interested will find a fuller discussion of fuels and fuel values in Snell's "Elementary Household Chemistry."
Electricity is not a fuel, but is classed here as a source of heat. It may be supplied for cooking purposes by any company that furnishes electric light, and should be available in the country wherever an electric trolley runs. The energy supplied is measured and paid for by the kilowatt; that is, one thousand watts. The terms used for electrical measurements cannot be really understood until one has studied electricity. It may be said, however, that the ampere1 is the unit of current strength, the volt is the unit of electrical pressure or electromotive force, the watt is the unit of electrical power and the basis of payment for current supplied for heating or lighting.
Voltage, amperage, and watt or kilowatt are the terms in common use. If you read the circulars that advertise electric cooking apparatus, you will find the request to state the voltage of your electric current in ordering a piece of apparatus. Or again, the number of watts used per hour is given, with the catalogue number and the size of an electric stove.
The cost of electricity per kilowatt (usually from ten to fifteen cents) varies in different localities.
The great advantage of electricity is that little heat is lost in radiation, and that the degree of heat is well under control. There are also no products of combustion present, and this is the only source of heat for cooking of which this is true. Both gas and kerosene vitiate the air to some extent.