Kerosene is a fractional distillate of crude oil which has a considerably higher vaporizing temperature than gasoline. It does not form an inflammable mixture with the air at ordinary temperatures, but is vaporized in practice by spraying it into a chamber heated to above 200°F. Kerosene forms a greater percentage of crude oil than gasoline and as there has been less demand for it up to the present time it is much cheaper. Pennsylvania crude oil produces only 20 per cent of gasoline while the kerosene contents will average nearly 42 per cent according to figures at hand. Kerosene has a very high calorific value per gallon, 8.5 gallons of kerosene having the same heating effect as 10 gallons of gasoline. Because of its high calorific value and its low cost per gallon, many types of engines have been developed for its use during the last few years, several of which have been very successful. Before the advent of the modern kerosene engine much difficulty was experienced with the fuel because of its high vaporizing temperature and its tendency to carbonize in the cylinder, but as the price of gasoline continued to rise, the inventive genius of the gas engine builder overcame these troubles so that the kerosene engine is now as reliable as any form of prime mover. [Illustration: Kerosene Vaporizer on Fairbanks-Morse Engine. The Engine is Started on Gasoline and When Hot, the Kerosene Feed is Turned on. ] Any gasoline engine will run on kerosene, after a manner, if the engine is thoroughly heated to insure the vaporization of the kerosene, and if the fuel is heated in the carburetor. Such an arrangement is make-shift, however, and is not productive of good results in continuous service. If kerosene is to be used as a regular fuel, a kerosene engine should be used to avoid vaporizing and carbonizing difficulties as well as the sooty, offensive exhaust, and the loss of fuel represented by the soot. Many kerosene engines are arranged to start on gasoline, and, after becoming heated, have the running feed of kerosene admitted through a three way valve. The gasoline feed is then stopped. The above arrangement admits of easy starting in all weathers and temperatures. In the Diesel engine there is no evaporating of fuel, and no deposits of carbon because of the high temperature of the combustion chamber. With engines that draw the mixture of vapor and air into the cylinder there are several methods of applying heat to the liquid, and the combustion of the vapor thus formed is perfected by the injection of water into the combustion chamber. It has been found by experiment that a small amount of water vapor introduced into the cylinder of a kerosene engine makes the engine run more smoothly and prevents a smoky exhaust and carbon deposits in the cylinder. The water is introduced into the cylinder through an atomizer in the form of a mist or fog, the particles of water being in a very finely subdivided state. [Illustration: