SERVICES. 187 



price is usually estimated by the number of burners, or by the yard run of 

 service, adding so much for union joints and burners. 



In order that the pipes for conveying the gas from the mains and distri- 

 buting it through the houses or other buildings to be lighted, may in the first 

 place be neither unnecessarily large or too small, the following rule is given : 



One gas-lamp consuming four cubic feet in an hour, if situated forty feet 

 from the main, requires a service not less than a quarter of an inch in the 

 bore. 



Two lamps, 40 feet from the main, require a three-eighth service. 



Three lamps, 30 feet from the main, require a three-eighth tube. 



Four lamps, 40 feet from the main, require a half-inch surface. 



Six lamps, 50 feet from the main, require a five-eighth service. 



Ten lamps, 100 feet from the main, require a three-quarter service. 



Fifteen lamps, 130 feet from the 'main, require an inch service. 



Twenty lamps, 150 feet from the main, require a service 1^ in diameter. 



Twenty-five lamps, 180 feet from the main, require a If service. 



Thirty lamps, 200 feet from the main, require a service 1^ in diameter. - 



It is desirable that all bends should be circular, but it is impossible to 

 make them so in many instances, as they would have an unsightly appear- 

 ance. No branch ought to proceed from a service of a quarter of an inch in 

 the bore, and no more than two from a three-eighth service. All pipes, 

 before they are fixed, must be proved by condensing air into them by means 

 of a hand-syringe while under water ; the leak will be easily detected by the 

 air-bubbles which rise through the water. For conducting the gas from the 

 street-mains into the interior of a house, or any building to be lighted, a 

 wrought-iron pipe of sufficient diameter is tapped into the main, and carried 

 in a straight line to the nearest wall of that building, through which it must 

 pass ; and on the inside be furnished with a good stop-cock. If all the fittings 

 rise from the main no siphon is necessary, but if any part of them fall below 

 the main a small receiver must be attached to the lowest point, fitted with a 

 screw-plug at the bottom, so that any moisture may be drawn off. The pipes 

 which convey the gas to the burners must be in as direct a line as possible, to 

 avoid unnecessary expense and obstructions. The union joints used to con- 

 nect two services together must be of the same diameter as the pipes, and 

 soldered firmly on to them. It is customary with workmen when they prove 

 their pipes to coil them up, place then- thumb over one end and suck the air 



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