ILLUMINATING GAS LIGHTING 43 



annually. Fortunately, up to the present time, as the older 

 fields began to fail new fields have been discovered. It is 

 thought, however, that most of the oil fields of the United 

 States are now known. It seems nearly certain that before 

 many years the supply of petroleum in the United States will 

 be declining. Oil fields of undetermined productiveness are 

 known to exist in Mexico and South America and so it may be 

 possible that we shall be importing much oil from these 

 countries before many years. 



IX. ILLUMINATING GAS LIGHTING 



53. Illuminating Gas. By illuminating gas we usually 

 mean either manufactured coal gas or water-gas saturated with 

 oil vapors (Arts. 115 and 116), although gasoline gas, as we 

 have just seen, and acetylene, as we shall see in the next section, 

 are also used for illuminating purposes. Whatever the source 

 of illuminating gas, it usually is piped into the house and 

 passes through a meter where its volume is measured. The 

 price paid for it is usually set at a certain sum per 1000 cu. ft. 



54. The Gas Meter. The common gas meter consists of an 

 air-tight, and therefore gas-tight, metal case, Fig. 24, which is 

 divided into two compartments by a metal partition. Each 

 of these compartments is again divided into two compart- 

 ments, A and B, Fig. 25, by a metal disk, 2, and a leather dia- 

 phragm, 4, Fig. 24. The leather diaphragm permits the metal 

 disk, D, Fig. 25, to move freely from left to right and from 

 right to left under the pressure of the gas. The gas enters 

 through the inlet pipe, 9, Fig. 24, into the valve chamber. 

 It then passes past the valves, 8, into the chambers A and A, 

 Fig. 25. Both disks, D and D, are, then, being forced to the 

 right by the gas pressure. Whenever an outlet is opened, 

 i.e., a gas jet or gas stove is lighted, the gas escapes through the 

 valves as indicated into the house pipes. As the disks move, 

 the flags, 3, twist the flag rods, 5. This rotating motion of the 

 flag rods is transmitted by the flag arms, 7, 7, 7, to the valves 

 and the dial pointers. When the disks have moved to the 



