gas. The latter gas is made by two different methods, one giving us coal gas, the other water gas. Coal gas is obtained by heating coal, usually semi-bituminous, in retorts so as to drive off the gas which it contains. Water gas is made by passing steam over heated coal ; then this is enriched by the addition of other gases in order to make it more efficient. Any gas is dangerous, because, when it is mixed with a certain amount of air, it becomes explosive, and because some of the gases present, if they escape un- burned, are highly poisonous. Water gas is particularly poisonous. Leaks in gaspipes should not be neglected. A light should never be taken into a room where there is a strong smell of gas, windows and doors should be opened, and, if necessary, the gas should be turned off from the whole house by the main stopcock near the meter. The surest way to detect small leaks is to paint over the sus- pected places with strong soapsuds, and notice where bub- bles are blown. Acetylene is another sort of gas used for fuel in special stoves. It is manufactured, usually on a small scale, by the automatic dropping of calcium carbide into water. The gas requires special burners, but gives a brilliant light. It seems still to be a matter of dispute whether it is highly poisonous as well as explosive. Gasoline gas, sometimes called air gas, is made by pump- ing air through gasoline. The law requires the gasoline tank to be outside and at a certain distance from the house, although the mixing chamber where more air is added may be nearer. The gas makes an excellent fuel and does not contain carbon monoxide, the compound in coal gas which is most poisonous. There are two kinds of alcohol which are common. One, wood alcohol, ought not to be used, because its fumes are poisonous. It is much cheaper than the other variety COMBUSTION AND FUELS 103 called grain, or ordinary alcohol, because that is so highly taxed. In recent years a way out of this difficulty has been found in the use of denatured alcohol. This is merely grain alcohol to which some substance has been added that makes it impossible as a beverage and thus it escapes hav- ing to pay the heavy tax otherwise imposed. The sub- stance added in no way impairs its use as a fuel. The use of electricity for cooking has certain advantages which are furnished by none of the fuels. In its use there are none of the products of combustion to get rid of, there is no flame to set fire to the unwary, no matches to be looked after, and its control is simple. It is, however, gen- erally too expensive for common use. Electricity is meas- ured by the kilowatt hour, the cost varying from about ten to fifteen cents. The dials on an electric meter are not unlike those on a gas meter and can be read easily. REFERENCES WHITE. "Fuels of the Household." U. S. Dept. of Commerce. Bureau of Standards Circular No. 55, sections on Coal, Wood, and Heating Value of Fuels. QUESTIONS 1. Name the different substances which may be used as fuels and arrange them in the order of their kindling temperatures. 2. Name the different kinds of coal used in the house, and, briefly, characterize each. 3. Determine the comparative costs of the different fuels used in your locality. Which is most commonly used and why ?

AI-modernized reading of the original text

gas. The latter gas is made by two different methods, one giving us coal gas, the other water gas. Coal gas is obtained by heating coal, usually semi-bituminous, in retorts so as to drive off the gas which it contains. Water gas is made by passing steam over heated coal ; then this is enriched by the addition of other gases in order to make it more efficient. Any gas is dangerous, because, when it is mixed with a certain amount of air, it becomes explosive, and because some of the gases present, if they escape unburned, are highly poisonous. Water gas is particularly poisonous. Leaks in gaspipes should not be neglected. A light should never be taken into a room where there is a strong smell of gas, windows and doors should be opened, and, if necessary, the gas should be turned off from the whole house by the main stopcock near the meter. The surest way to detect small leaks is to paint over the suspected places with strong soapsuds, and notice where bubbles are blown. Acetylene is another sort of gas used for fuel in special stoves. It is manufactured, usually on a small scale, by the automatic dropping of calcium carbide into water. The gas requires special burners, but gives a brilliant light. It seems still to be a matter of dispute whether it is highly poisonous as well as explosive. Gasoline gas, sometimes called air gas, is made by pumping air through gasoline. The law requires the gasoline tank to be outside and at a certain distance from the house, although the mixing chamber where more air is added may be nearer. The gas makes an excellent fuel and does not contain carbon monoxide, the compound in coal gas which is most poisonous. There are two kinds of alcohol which are common. One, wood alcohol, ought not to be used, because its fumes are poisonous. It is much cheaper than the other variety called grain, or ordinary alcohol, because that is so highly taxed. In recent years a way out of this difficulty has been found in the use of denatured alcohol. This is merely grain alcohol to which some substance has been added that makes it impossible as a beverage and thus it escapes having to pay the heavy tax otherwise imposed. The substance added in no way impairs its use as a fuel. The use of electricity for cooking has certain advantages which are furnished by none of the fuels. In its use there are none of the products of combustion to get rid of, there is no flame to set fire to the unwary, no matches to be looked after, and its control is simple. It is, however, generally too expensive for common use. Electricity is measured by the kilowatt hour, the cost varying from about ten to fifteen cents. The dials on an electric meter are not unlike those on a gas meter and can be read easily. WHITE. "Fuels of the Household." U. S. Dept. of Commerce. Bureau of Standards Circular No. 55, sections on Coal, Wood, and Heating Value of Fuels. 1. Name the different substances which may be used as fuels and arrange them in the order of their kindling temperatures. 2. Name the different kinds of coal used in the house, and, briefly, characterize each. 3. Determine the comparative costs of the different fuels used in your locality. Which is most commonly used and why ?

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