PETEOLEUM. 



51 



The natural gas produced is of two types according to whether it 

 carries a conspicuous burden of gasoline vapor or is lean in this con- 

 stituent. The first type, as may be surmised, flows from an oil- 

 productive stratum and is called " wet " or casing-head gas, since it 

 makes its appearance from the casing-heads of oil wells. The second 

 type is termed " dry " gas, and comes from portions of porous rock 

 formations practically free from oil ; it is produced through gas wells 

 more or less independently of petroleum output.^ 



While not vital to the country, because its use may be supplanted 

 by other types of fuel, natural gas is of considerable commercial im- 

 portance, as shown in the accompanying table : 



Relative commercial importance of natural gas, expressed on a per capita basis 



for 1915.0' 



Natural gas (cubic feet) 



A rtificlalclt y gas (cubic feet) 



By-product, coke-oven gas (cubic feet) 



Cruae petroleum (barrels) 



Anthracite coal (tons) 



Bituminous coal (tons) 



Consumption 

 per capita 



6 6,285 

 1,818 

 840 

 2.8 

 .9 

 4.4 



Value per 

 capita. 



$1.01 

 1.65 

 .08 

 1.79 

 1.84 

 5.02 



Average 

 pnce. 



c $0. 16 



C.91 



c.lO 



.64 



<12.07 



<il.l3 



a Figures calculated on basis of population of 100,000,000 from data published in Mineral Resources of 

 the United States for 1915, U. S. Geological Survey. 



ft Includes various types of artificial gas as commonly supplied in municipalities. 



c Per 1,000 cubic feet. Note the marked discrepancy in price per 1,000 cubic feet. The Intrinsic value, 

 as contrasted to the commercial value, is 1.5-2, 1, and 1 respectively. 



d Price at mines. 



About one-third of the natural gas consumed in the United States 

 is used for domestic purposes — lighting, cooking, and heating — while 

 about two-thirds is burned in industrial plants under steam boilers 

 and especially in metallurgical operations, glass and pottery fur- 

 naces, and cement kilns, where the requirements of an intense heat 

 call for gaseous fuel. In Ohio and Western Pennsylvania, in par- 

 ticular, the abundant occurrence of natural gas has determined the 

 location and widespread development of gas-fired industries.^ 



^The two types of gas are gradational, not sharply distinctive. "Wet" gas carries 

 upwards of three-fourths of a gallon of gasoline per 1,000 cubic feet of gas, while much 

 of the " dry " gas carries only from one to two pints of gasoline per 1.000 cubic feet. 

 See George A. Burrell and others, Extraction of gasoline from natural gas by absorption 

 methods : Bulletin 120, Bureau of Mines. 1917. 



*Thus Ohio and Pennsylvania are the two leading States in the manufacture of clay 

 products ; the Pittsburgh district is the greatest glass-manufacturing district of the 

 United States, while the iron and steel industry in the vicinity of Pittsburgh consumes 

 an enormous volume of natural gas in its blast furnaces, foundries, and rolling mills. 

 Natural gas has been " the fourth element in making western Pennsylvania more lib- 

 erally supplied with fuel than any other place in the world. In that region a thick 

 forest covered hills which were underlain with the magnificent coal deposits of the 

 Appalachian field, while farther down was the crude petroleum and the natural gas 

 that drove it spurting from the orifices in the rocks." The rising cost of natural gas, 

 coming with progressive exhaustion of fields, has caused a migration in the glass- 

 making industry, many plants having moved from Pennsylvania to West Virginia and 

 from Indiana to Oklahoma in order to get cheaper fuel ; other plants in regions de- 



