STEAM AND GASOLINE ENGINES 191 



motor car. Constant improvements were made in such steam- 

 motor cars and their engines and by the middle of the nineteenth 

 century steam-motor busses were in use to some extent, and the 

 steam-motor car while still a novelty gave promise of general use. 

 Such promise would undoubtedly have been realized had not the 

 gasoline engine been rapidly developed. In 1900 there were 

 about 700 automobiles in the United States, all of which were 

 steam cars except a few imported ones. In 1910, 400,000 cars 

 were in use here and very few were steam-driven nearly all 

 makers having adopted the gasoline engine. 



The gasoline engine has many advantages over the steam 

 engine, especially where a portable power plant is required. It 

 develops a greater horse-power in proportion to its weight than 

 does the steam engine. It wastes less of the power that is 

 developed than does the steam engine. In the latter there is a 

 great loss of energy through radiation of heat, by friction, and in 

 other ways, so that only from 6 to 1 2 per cent of the energy gen- 

 erated by burning the coal is actually delivered as mechanical 

 energy to do the work required. A good gasoline engine delivers 

 from 20 to 40 per cent of the energy of the gasoline. 



Gasoline is a highly volatile liquid composed largely of 

 carbon and hydrogen. When it burns or unites chemically with 

 oxygen it gives rise to carbon dioxide (or carbon monoxide, a 

 very poisonous gas, if the oxygen supply is limited) and water 

 vapor or steam. These gases are produced in large volume 

 from a very small amount of gasoline so that, if the latter 

 is mixed well with air so it will burn quickly and thoroughly 

 and the mixture is fired in a confined space, an explosion occurs 

 just as happens when gunpowder is set off in a small space. 

 It is the elasticity of these confined gases that exerts the pressure 

 on the piston head in the cylinders. In general, the plan of 

 operation of the gas engine is similar to that of the steam engine; 

 the piston, however, is driven only in one direction by the force of 

 the explosion. It is forced back again by the action of other cyl- 

 inders that fire later and are coupled up with the same crank shaft. 



