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Prevention of Dust

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PREVENTION OF DUST. Loam and clay roads are im proved by a little moisture—just enough to keep them damp and dark without making them soft or spongy. In dry climates the roads not only become excessively dusty, which is a great discom fort, but also wear into pot-holes, which are dangerous, since being filled level-full of dust their presence is not revealed until a wheel or a horse's foot plunges into them. In some localities the dust at times is practically hub deep, and is not only an annoyance but greatly increases the tractive resistance. In arid climates and even in dry times in humid climates, sprinkling is an effective means of maintenance. A layer of straw is sometimes put upon the road to subdue or prevent the dust; but of course the effect is only tem porary.

Oiling the Road.

Recently crude petroleum has been employed on wagon roads, instead of water, to prevent dust—in southern California practically, and in several other states experi mentally. Oil has been used by a number of railroads to reduce the dust raised by trains—particularly near passenger stations. When applied to wagon roads, oil reduces the dust, makes the road bed at least partially non-absorbent, and gives a dark-colored sur face which is more pleasing to the eye than the ordinary light, dusty soil. A further advantage gained from a practically dustless road is the prevention of dust upon fruit trees and upon park foliage.

The oil is applied preferably at a temperature of 200° F. or over with a sprinkling wagon. Oil should not be applied to a hard sur face to prevent dust, since it is not readily absorbed and does little or no good. The road should be perfectly dry, and the oil must be thoroughly incorporated with the dust. If it is merely sprinkled on the surface, only the top layer of dust will be impregnated; and the wheels will break up the crust thus formed and expose the dust below, and the road will be but little, if any, better than before treatment. After the oil has been applied, the surface is stirred

with a light harrow, to mix the dust and the oil.

On the sandy soil of southern California, the first application usually consists of 4,000 to 6,000 gallons to a mile of road 16 to 18 feet wide, or / to 11 gallons per square yard. If the surface is very loose more than 11 gallons may be required to keep down the dust. The rule is to apply in the first application all the oil the road will absorb. The road is sprinkled two or three times during the sum mer, the quantity of oil required for the second and third applica tion being much less than for the first. The oil used is the residuum remaining after the naphtha, gasolene, and kerosene have been ex tracted from crude petroleum, and contains 17 to 18 per cent of bitumen (§ 570). The latter is the most important constituent. The oil costs in southern California from $1.00 to $1.25 per barrel of 24 gallons f.o.b. at the refinery; the outlay is about $200 per mile of 16-foot trackway for three applications, of which about $15 to $20 is for the labor necessary to apply the oil.

The application of oil decreases the tendency to form mud, since it aids the road in shedding rain water, and also since the bitumen in the residuum cements the particles of the soil together and increases its resistance to being cut up by traffic. However, the tendency of oil to decrease mud is only slight, and the effect of the oil will not last through a wet time. Oiling the road is most needed and is also most effective in a dry climate. The best results are obtained on a clay soil or on sandy or gravelly loam; and dil is ineffective on fine sand, coarse gravel, or alkali soil.

Residuum oil seems to be very beneficial to macadam roads (see § 381).