226 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 



Gas 



The pipes that carry the gas underground to the con- 

 sumer are of iron ; sometimes they are 3 or 4 feet in diam- 

 eter. The pipes from the street "main" into the house 

 and to the gas outlets are also of iron. The smaller pipes 

 are joined by screw joints, made gas-tight by some pasty 

 mixture, such as red lead and glycerine. The gas com- 

 pany tests the whole piping system of a house by pump- 

 ing air into it until there is considerable pressure. The 

 pressure is measured by a gauge, or manom- 

 eter (Fig. 211). The gas-fitter needs to be 

 careful, or he will break some of the joints 

 when he attaches the fixtures. 



The ''key/' by which gas is turned on or off in a 

 fixture, is a tapering plug having an external, flat 

 handle. The plug fits into a hole with tapering sides. 

 To hold the plug tight in its socket, there is a short, 

 spiral spring. This is held in place by a screw that 

 presses against the body of the fixture. If the key or 

 its socket wears away, so that gas escapes around it, 

 the joint may be tightened by a slight turning of the 

 screw. We must remember that illuminating and 

 fuel gases usually contain much carbon monoxide, a very poisonous 

 gas, and that all leaks in the gas fixtures should be attended to im- 

 mediately. 



256. The Gas Meter. In most houses the gas meter 

 is found in the basement. It is a metal box having, on its 

 face, dials like those of Fig. 212. When the hand on the 

 "5 cubic feet" dial has revolved 20 times, the hand on the 

 "1000 cubic feet" dial will have moved from to 1, and 

 will indicate 100 cubic feet. The hand on the "1,000" 

 dial must make one complete revolution to move the hand 

 on the "10,000" dial from to 1, and so on. Note in 



Fig. 211. 

 The gas pushes 

 up the mercury 

 until the down- 

 ward pressure 

 of the mercury 

 equals the gas 

 pressure. 



