HOW HEAT IS PRODUCED 



123 



fore much cheaper. Large quantities of soft coal are 

 used annually in industry for generating power. 



Coke is made from bituminous coal. In recent years 

 coke has become a common fuel for home heating. It 



Paul's Phot 



FIG. 189. COAL MINER AT WORK 



is obtained as a by-product in the manufacture of gas 

 and other products from coal. Soft coal is heated away 

 from air in large retorts, and after the gases and tarry 

 substances have been driven off, coke remains in the 

 retort. The gases and tarry substances are recovered, 

 and from them many useful products are obtained. 

 Figure 192 gives some idea of the variety of sub- 

 stances obtained from coal. Coke is a gray-black por- 

 ous solid. It burns in a furnace with a very hot flame 

 and is an efficient fuel, for there is very little ash or 

 unhurnable material in it. 



Gas for fuel may be obtained from coal. As the coal 

 is heated, gases which contain ammonia, coal tar va- 

 pors, and coal gas are driven off. In passing through 

 the plant the ammonia is absorbed in the water, the 

 tar is condensed, and other impurities such as sulphur 

 are removed. The gas is then passed into the gas 



FIG. 190. PRINCIPAL COAL AREAS OF THE UNITED STATES 



holder, from which it may be delivered to the con- 

 sumer directly or mixed with natural gas and then 

 distributed. 



Natural gas is also used for fuel. In certain parts 

 of the United States gas is found in natural deposits 

 in the earth. By drilling down to it we may obtain 

 this gas and pipe it to cities where it is used for cook- 

 ing, for heating, and for industrial purposes. The gas 

 is frequently under such pressure in the well that it 

 gushes out as soon as the cap rock which covers the 

 deposit has been broken by the drill. It is often diffi- 

 cult to control these "gushers," and millions of cubic 

 feet of gas are sometimes lost into the air before the 

 well is capped. Also the gas may ignite, and serious 

 damage may result from fire. In some cases the na- 

 tural gas does not have sufficient pressure to force 

 itself out of the well. It then is necessary to pump it 

 from the well to the place 

 where it is to be used. 



Gas is usually sold at a cer- 

 tain rate per thousand cubic 

 feet. At the place of use it is 

 run through a meter which 

 measures the amount con- 

 sumed in cubic feet. Figure 

 191 shows a common gas 

 meter. 



Petroleum is used as ;\ 

 source of energy. You have 

 learned from the study of the 

 graph, Figure 187, that ap- 

 proximately twenty-one per 



cent of our available energy in this country comes 

 from oil. Oil and other fuels are derived from pe- 

 troleum which is obtained from natural deposits in 

 the earth. 



In recent years there has been a rapid increase in 

 the use of oil both for home heating and for industrial 

 purposes. Oil is also increasing as a fuel for railroads 

 and for ships. While it is somewhat more expensive 

 than coal, it is a much cleaner fuel and is much easier 

 to handle and to store. Figure 215 shows an oil-burn- 

 ing furnace used for home heating. 



Petroleum is secured in somewhat the same man- 

 ner as natural gas. Wells are drilled down to the oil 

 deposit, which is often found along with gas under 

 great pressure. This may cause the oil to shoot out of 

 the well with tremendous force ; such a well is also 

 known as a "gusher." In cases where the oil is not 

 under pressure it is necessary, as in the case of natural 

 gas, to pump it from the well. 



Crude petroleum is a heavy, black, oily liquid which 

 is a mixture of many substances. Besides the fuel oil 

 that is obtained, it also contains gasoline, naphtha, 



St. Louis Loitnty Gas C 



FIG. 191. GAS METER 

 INSTALLED 



