304 THE GAS ENGINE 



This is not the place to discuss the various grades of 

 lubricating oils and their properties and uses, but it may be 

 well to mention one fact and that is the necessity of using a 

 good grade of oil especially adapted for gas engine cylinders. 

 The contact surface of the piston in the cylinder must be 

 lubricated, of course, and since the temperature is very 

 high, the oil must be of a character that does not readily 

 carbonize or volatilize under the action of heat. An oil 

 whose density is 26° to 28° Be., with a flash test of 400° to 

 475° F., has been recommended for some engines. Dealers 

 in engines can recommend the best cylinder oil for use in 

 their particular engine. 



223. Summary. — The gas engine has become such an 

 important factor in the raising and marketing of crops, 

 and for many other purposes on the farm that a brief dis- 

 cussion of it, particularly in its chemical bearing, is not 

 out of place. It is a machine in which pressure is applied to 

 a piston head by the explosion of a mixture of inflammable 

 gas and air. This explosion comes either every time the 

 piston compresses the mixture by an inward stroke, or 

 every other time. The former type is called a two-cycle 

 engine, the latter a four-cycle engine. The mixing of gas 

 and air is a very important part of such an engine. Gasoline 

 is the common fuel employed, and since it is a liquid, it 

 must be volatilized before use. This is accomplished by 

 drawing it into the cylinder in a fine spray along with the 

 air. 



Gasoline is one of the distilled and purified fractions 

 obtained from crude petroleum. Although properly it has 

 a density of 90° to 80° Be. it is more frequently 65° to 60° Be., 

 for gas engines. Gasoline is a mixture of hydrocarbons 

 and may consist of few or many. It is possible to maintain 

 a uniform density in the product by mixing different light 

 and heavy fractions in various proportions. A mixture of 

 very light hydrocarbons with very heavy ones does not give 

 as efficient a fuel as a mixture of several having more nearly 

 equal densities, even though the result is a liquid of the same 

 density. 



A proper amount of air is essential in obtaining maximum 



