THE GAS METER 



93 



containing mercury, and so made that one end can be fitted 

 to a gas jet (Fig. 52). When the gas cock is closed, the 

 mercury stands at the same level in both arms, but when the 

 cock is opened, the gas whose pressure is being measured 

 forces the mercury up the opposite arm. If the pressure of 

 the gas is small, the mercury changes its level but very little. 

 It is clear that the height of a column of mercury is a measure 

 of the gas pressure. 



By actual measurement it has been found that one cubic 

 inch of mercury weighs about half a pound. Hence a column 

 of mercury one inch high indicates a pressure of about one 

 half pound to the square inch ; a column two inches high in- 

 dicates a pressure of about one pound to the square inch, and 

 so on. 



This is a very convenient way to measure the pressure of 

 the illuminating gas in our homes and offices. The gauge is 

 attached to the gas burner and the pressure read by means of 

 a scale attached to the gauge. (See Laboratory Manual.) 



In order to have satisfactory illumination, the pressure 

 must be strong enough to give a steady, broad flame. If the 

 flame from any gas jet is 

 flickering and weak, it is 

 usually an indication of 

 insufficient pressure and 

 the gas company should 

 investigate conditions and 

 see to it that the con- 

 sumer receives his proper 

 value. 



87. The Gas Meter. 

 Most householders are 



100 THOUSAND 10 THOUSAND 



1 THOUSAND 



FlG. 53. The gas meter indicates the num- 

 ber of cubic feet of gas consumed. 



deeply interested in the actual amount of gas consumed (gas 

 is charged for according to the number of cubic feet used), 



