No coppered pipes should be used but such as have wrapt over and brazed joints. They should be well annealed, to render them pliable without being liable to break.
All the bends for connecting pipes must be circular, see fig. 22, plate V.
No branch pipe ought to proceed from a pipe of a quarter of an inch in the bore, and no more than two branch pipes should proceed from a pipe three-eighths of an inch in the bore.
All branch pipes before they are fixed for conveying gas, must be proved by condensing air into them by means of a condensing hand pump. The pipe should be placed in a trough of water, the leak will then be easily observed by the air bubbles which rise through the water whilst the air is condensed in the pipes.
All branch pipes should have a rectilinear course; pipes that are twisted have an unsightly appearance.
All pipes should have a descent of no less than a quarter of an inch in four feet.
The seams or brazed part of the pipes must always be out most and not towards the wall; because if a leak should happen to take place in the brazed part of the pipe, it may then be easily discovered and more readily repaired.
When all the pipes have been furnished to a house or place intended to be lighted, the whole system of the pipes should be examined with the utmost rigour, to ascertain whether all the junctures are air tight. This should be done by condensing air into the pipes by means of a condensing syringe, and if the piston of the syringe lowers after condensation, it is a sure indication that the pipes are faulty, and consequently totally unfit for receiving the gas. The leak may be detected by passing a lighted taper carefully along the whole extent of the pipe filled with condensed air, when the flame of the taper will be affected as it passes over the faulty place of the pipe.
The aperture from which the gas can escape may however, be so small, as to render it a matter of difficulty to discover it in the manner just stated; but when the pipes are filled with coal gas, the escape of it, when all the stop-cocks of the lamps and burners are shut, will soon become obvious, by the peculiar odour of the gas, if the apartment, or place, where the pipes are placed, is suffered to be closed for about twenty-four hours. The gas should not be introduced into pipes in which any defect of this kind is found, until it be completely removed. The most severe trial to ascertain the air tightness of any system of pipes is, the trial by exhaustion, by means of an air pump, for the guage of the pump will discover the minutest leak, which the preceding method of proving pipes can not discover.