148 GENERAL SCIENCE 



Measurement of Gas. The gas used in the household is usually 

 measured on the premises by a gas meter. In the United States 

 and parts of Europe the so-called dry gas meter is most commonly 

 used for this purpose. 



There are a number of different types of dry gas meters in use, 

 which, while differing considerably in external appearance and 

 design of parts, operate on the same general principles. These 

 general principles of operation would be understood from a descrip- 

 tion of any one of the types; and therefore only one of the most 

 commonly used will be described. 



Description of a Gas Meter. The external appearance of the 

 meter is well known. The interior is shown in Fig. 115, with the front 

 and top of the meter and the top of the valve chamber removed. 

 Essentially the meter consists of four chambers which are filled and 

 emptied of gas by the action of the meter mechanism. The number 

 of times this filling and emptying of the measuring chambers is 

 repeated is indicated on the dial in cubic feet. Two of the meas- 

 uring chambers are shown in the figure. One is the space between 

 the disc (201) with attached leather diaphragm (203) and the 

 middle partition (the plate just behind the diaphragm) of the 

 meter. The other is the space between this same disc and dia- 

 phragm and the outside walls of the meter. The other two meas- 

 uring chambers are like the two described, and are situated sym- 

 metrically to them on the opposite side of the middle partition. 

 The filling and emptying of the measuring chambers is effected 

 by the backward and forward movement of the discs. These 

 discs operate in conjunction with the valves and recording mech- 

 anism (see Fig. 115) above the measuring chambers. Each set 

 of two measuring chambe'rs thus constitutes a kind of double- 

 acting bellows, the number of times these are filled and emptied 

 being a measure of the amount of gas passed through them. The 

 power for operating this very simple and effective instrument is 

 furnished by the pressure of the gas itself which acts upon the 

 discs, pushing them back and forth, just as the power to 

 operate the steam engine is furnished by the steam which 

 presses upon the sides of the piston. The index (101) upon 

 which the volume of gas passed is recorded is connected with 



