294 



TRANSPORTATION 



placed yearly in this country. These are paid for large- 

 ly by the automobile owners in gasoline taxes im- 

 posed by the various states. 



The cement-road builder first makes and grades an 

 excavation. Upon this a mixture of coarse stone, sand, 

 and cement is placed, often reenforced with iron 

 netting or screening. This foundation is then covered 

 with a surface of sand and cement. Figure 486 shows a 

 cross section of a cement road and Figure 487 a road 

 before and after it was improved with a cement sur- 

 face. 



In some cities wood and stone blocks or bricks are 

 used for paving. These are usually laid upon a base of 

 concrete and bound with tar, asphalt, or cement. In 

 general, these methods of paving are more expensive 

 than concrete or asphalt as is seen by the following 

 table of cost estimates on different types of road. 

 These figures are for 18-foot roads on a basis of 1929 

 construction costs. 



Macadam road, per mile .$16,000 



Asphalt concrete, per mile 18,000 



Portland cement concrete, per mile 33,000 



Brick, concrete base, per mile 45,000 



Wood block, concrete base, per mile 70,000 



How do the various parts and systems of the mod- 

 ern automobile work together to make it run? The 

 last thirty-five years have seen the development of 

 the automobile from a crude "horseless carriage" to 

 a modern vehicle which has almost displaced the horse 

 as a means of transportation. The automobile has be- 

 come so common that everyone should know some- 

 thing of the scientific principles that control it. The 

 automobile is made essentially of three systems which, 

 working together, make possible the many uses to 

 which it is put. These systems are the chassis, the 

 power system, and the transmission system. 



The chassis. This is the steel framework or founda- 

 tion upon which the car is built. It also includes the 

 wheels and brakes. Because automobiles are subject 

 to many strains, the chassis must be tough and strong, 

 and, therefore, is built of special steel and is well 

 braced. The chassis is carefully designed and built 

 to carry the load of the car and also to withstand the 

 many strains. 



The power plant. This important part of the auto- 

 mobile includes the fuel system, the engine, and the 

 electrical system. An experiment at the beginning of 

 this topic has taught you that when gasoline vapor 

 and air are mixed in a confined chamber, and a spark 

 or flame is introduced, a powerful explosion takes 

 place. 



Liquid gasoline is placed in a tank on the car and 

 is fed to the carburetor either by gravity or by air 

 pressure working with a fuel pump or vacuum tank. 



The carburetor atomizes 1 the liquid gasoline by draw- 

 ing it through a small jet or opening in much the same 

 way that a throat or perfume spray vaporizes the 

 liquid used in it. After the liquid gasoline has been 

 atomized in the carburetor, it is mixed with air in the 

 correct proportions for a powerful explosion. Figure 



FLOAT CHAMBER COVER AND 

 INLET VAtVE MECHANISM - 



FLOAT tP GASQUNt HIGH 

 HEEDLC DROPS AND 

 CLOSES VAUVK 



MIXTURE TO INTAKE MANIFOI.O 



BUTTERFLY VAWE OR 

 THROTTl* CONTROLS 

 SPEED OF ENGINE - 



CORK FLOAT 

 CONTROL FLOW 

 OF GASOLINE 



IN CARBURETOR 



Courtesy Standard Oil Co. of New York 



FIG. 488. CROSS SECTION OF CARBURETOR (ABOVE) ; HOW IT 

 WORKS (BELOW) 



488 is a cross-section diagram showing the parts of a 

 carburetor and how it sprays the gasoline. The air- 

 gas mixture is taken from the carburetor to the en- 

 gine through the intake manifold. Figure 489 is a dia- 

 gram showing the complete fuel system of the car and 

 also how the gas gets from the carburetor to the 

 cylinder of the engine. 



Exercise. Study Figure 488 and suggest how the pipe 

 damper in a smoke pipe illustrates an important point in 

 the construction and operation of a carburetor. 



1 Atomize, to break up into very small particles. A spray gun 

 atomizes the liquid which it sprays. 



