If the gauge shows a fall of pressure of one
quarter of an inch or more in these circumstances, the pipes must be
examined until the leak is located. In the presence of a meter, the
installation can conveniently be tested for soundness by throwing into
it, through the meter, a pressure of 12 inches or so of water from the
weighted holder, then leaving the inlet cock open, and observing whether
the index hand on the lowest dial remains perfectly stationary for a
quarter of an hour--movement of the linger again indicating a leak. The
search for leaks must never be made with a light; if the pipes are full
of air this is useless, if full of gas, criminal in its stupidity. While
the whole installation is still under a pressure of 12 inches thrown from
the loaded holder, whether it contains air or gas, first all the likely
spots (joints, &c.), then the entire length of pipe is carefully brushed
over with strong soapy water, which will produce a conspicuous "soap-
bubble" wherever the smallest flaw occurs. The tightness of a system of
pipes put under pressure from a loaded holder cannot be ascertained
safely by observing the height of the bell, and noting if it falls on
standing.
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