in so-called "coke ovens as a primary product, the gas, tar, etc., being secondary products or in all too many cases wasted; (2) Gas coke, a much softer material left in the retorts used in the manufacture of illuminating gas from coal. Gas coke is a valuable domestic fuel, igniting almost as easily as bituminous coal and burning with a very intense flameless fire. Furnace coke, on the other hand, is a very hard substance and is more difficult to ignite than anthracite. While of great industrial importance, this kind of coke is unsuitable for domestic use.

In all solid fuel fires, and especially in coal fires, it is important to keep the grate and the surface of the fuel free from an accumulation of ashes. Ashes not only impede the draft but, covering the surface of the fuel, they prevent the oxygen from coming in contact with the combustible solid. The shaking of the fire not only clears the grate of the ashes which tend to clog it, but also shakes off the covering of ashes from the face of the coals and exposes the latter to the action of the oxygen.

For further information about solid fuels the reader is referred to Chapter V of Benson's “Industrial Chemistry” (New York, 1913) and to the numerous references there cited.

F

CHAPTER XII

FUELS (Continued)

Liquid Fuels

THE most important liquid fuels are the petroleum products - especially kerosene. The alcohols are at present fuels of secondary importance.

Petroleum is an oil obtained from underground sources. It is a mixture of a great many compounds of carbon and hydrogen. In the refining process the more volatile compounds are separated from those less volatile. A large number of products are thus obtained.

Benzine and gasoline are two of the most useful of the light or volatile products; kerosene is heavier and less volatile; the still less volatile constituents of the crude petroleum make up such products as lubricating oils, axle greases, vaseline (or petrolatum), and paraffin wax.

The vapor of benzine and gasoline is given off in sufficient abundance at ordinary temperatures to form explosive mixtures with air. On account of this danger benzine and gasoline should not be used as household fuels.

66

Kerosene (called paraffin" in England and "coal oil" in some parts of America), if well made, gives off very little vapor at ordinary temperatures - enough to affect the sense of smell, but not nearly enough to form an explosive mixture with air. The momentary application of a flame, either above or directly to the surface of the cold oil, will cause no ignition. The flame or flash test commonly applied to kerosene is a test to determine to what temperature the oil must be heated in order that it may give off sufficient

vapor to form a combustible mixture with air. The laws of most countries prescribe a minimum flash point for oils offered for sale for illuminating purposes.

Kerosene stoves are of two types. One type is constructed like a large kerosene lamp and gives a yellow, sooty flame. The other type gives a blue flame like a Bunsen burner. In the lamp-like stove the oil rises from the reservoir to the burner through a wick, and is converted into gas in the flame itself. In the blue-flame stoves the oil is vaporized and mixed with air before it reaches the flame. The latter type is practically a combined gas factory and Bunsen burner. Figure 33 shows such a stove.

66

grain alcohol are con

Wood alcohol and denatured venient household fuels for small fires, such as those of chafing dishes, table kettles, and coffee percolators. Wood alcohol (methyl alcohol) is a product of the destructive distillation of wood (see Expt. 24, p. 41), and therefore a byproduct of the charcoal industry. Grain alcohol (ethyl alcohol) is produced by the fermentation of sugars. The reason it is called "grain " alcohol is that it is so often made by converting the starch of grain, such as corn or rye, into sugar, by the action of malt, and fermenting the sugar so obtained. But it is also made from molasses and from potatoes. Ethyl alcohol is the active, intoxicating principle of all fermented and distilled beverages. Denatured alcohol is ethyl alcohol to which some substance has been added to render it unpalatable. Methylated spirits is a common variety of denatured alcohol. It is grain alcohol to which a small proportion (about 10 per cent) of wood alcohol and

usually a small proportion of some other substance, such as benzine, has been added.

Both wood alcohol and grain alcohol contain the three elements, carbon, hydrogen, and oxygen. Both liquids are readily ignited and burn with smokeless flames.

Three quarts of grain alcohol, or of methylated spirits, will give nearly as much heat as four quarts of wood alcohol.

The present importance of the alcohols as fuels is, as already stated, a secondary one. This is due to their relatively high price as compared with the petroleum products. The quantity of these two alcohols which could be produced from agricultural products is practically unlimited, and it is possible that some day these substances may find more use as fuels than they do at present.

Gaseous Fuels

The gases most used in the household for fuel purposes are natural gas, coal gas, water gas, and gasoline or "air" gas.

Natural gas exists underground in certain localities, usually in porous strata, whence it is obtained by boring wells. It consists of the compound methane, CH4, mixed with small quantities of other gases. Used with suitable burners it is the most convenient and most efficient of all the natural fuels. It yields about 1000 B. T. U. per cubic foot. Natural gas is supplied to many of the cities of Pennsylvania, Ohio, Indiana, and western New York. In Canada it occurs in New Brunswick, Alberta, and other places.

Coal gas, made by the destructive distillation of bituminous coal, constitutes the gas supply of most European and of many American cities. The coal is heated in closed retorts, the gases produced being conducted off through pipes. The gases are purified by cooling, washing with water, and passing through lime or iron oxide. The by-products are gas coke, which remains in the retort; coal tar, which con

denses from the gases on cooling, and from which numerous useful compounds are manufactured - antiseptics (such as carbolic acid), dyes (see Chapter XLIII), etc.; and ammonia, which remains in the wash water (see Chapter XXIII). The lime and iron oxide remove the sulphur compounds from the gas.

The chief constituents of coal gas are free hydrogen and methane, each of these being present to the extent of about

40 per cent. In addition to these two main constituents there are carbon monoxide (usually 6 to 8 per cent) and some compounds of carbon and hydrogen, other than methane. It is these latter hydrocarbons which make the gas burn with a luminous flame. To obtain a flame which will not deposit soot, burners on the principle of the Bunsen burner are used. In such burners the gas is mixed with air before ignition. Coal gas yields 600-625 B. T. U. per cubic foot. A ton of coal yields about 10,000 cubic feet of gas, which contain only about one fifth of the original fuel value of the ton of coal.

Water gas is used in many American cities. It is prepared by passing steam through white-hot coke or anthracite coal. The chief constituents of water gas are carbon monoxide and hydrogen. Gas made from coke contains about 45 per cent of each of these two gases, the remaining 10 per cent being methane, carbon dioxide, free nitrogen, and free oxygen.