steam, and the mixture is driven through a long coil of very hot pipe. The oxygen of the steam unites with the carbon of the oil, forming carbon monoxide, and the hydrogen is set free. The resulting gas is permanent, and is of high value for heating purposes. It is produced at a pressure of 8 to 10 pounds per square inch.
OIL GAS
68. Oil gas is made, in much the same manner as coal gas, by the process known as destructive distillation. This process consists in heating the oil to a very high temperature and causing the heavy hydrocarbons it contains to break up into the lighter or gaseous forms. In the manufacture of this gas, not only is petroleum utilized, but also many animal and vegetable fats and oils; among these are to be found the waste fats that occur in the manufacture of woolens, and ordinary rosin.
PRODUCER GAS
69. Manufacture. — Producer gas, as the term is usually applied in the United States, is a sort of diluted water gas not enriched with illuminating oils. The gas is made by a continuous process in what is known as a producer. There are two types of producers, known as suction producers and pressure producers. The former type has the advantage of simplicity, and for this reason is generally preferred for all but the largest engines. The movement of the gases and steam in the producer is induced by the suction of the engine itself, so that the gas is produced automatically in exact proportion to the demands of the engine. Its only drawback is the fact that the necessity of pumping the air and gas through so extended an apparatus slightly reduces the effective power of the engine, since the charge cannot be taken in at atmospheric pressure. This drawback is avoided in pressure producers, in which a blower is used to maintain the pressure of th6 gases in the generator at or slightly above that of the atmosphere.
