PRESSURE IN GENERATORS.--Inasmuch as acetylene is prone to dissociate or
decompose into its elements spontaneously whenever its pressure reaches 2
atmospheres or 30 lb. per square inch, as well as when its temperature at
atmospheric pressure attains 780 deg. C., no pressure approaching that of 2
atmospheres is permissible in the generator. A due observance of this
rule, however, unlike a proper maintenance of a low temperature in an
acetylene apparatus, is perfectly easy to arrange for. The only reason
for having an appreciable positive pressure in any form of generating
plant is that the gas may be compelled to travel through the pipes and to
escape from the burner orifices; and since the plant is only installed to
serve the burners, that pressure which best suits the burners must be
thrown by the generator or its holder. Therefore the highest pressure it
is ever requisite to employ in a generator is a pressure sufficient
(_a_) to lift the gasholder bell, or to raise the water in a
displacement holder, (_b_) to drive the gas through the various
subsidiary items in the plant, such as washers and purifiers, (_c_)
to overcome the friction in the service-pipes, [Footnote: This friction
manifestly causes a loss of pressure, _i.
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