From this final holder the enriched gas will be pumped
into the cylinders or into a storage cylinder, by means of a thoroughly
cooled pump, so that the heat set free by the compression may be safely
dissipated.
Whenever still better light is required in railway carriages, as also for
the illumination of large, constantly used vehicles, such as omnibuses,
the acetone process (_cf._ Chapter XI.) exhibits notable advantages.
The light so obtained is the light of neat acetylene, but the gas is
acetylene having an upper limit of explosibility much lower than usual
because of the vapour of acetone in it. In all other respects the
presence of the acetone will be unnoticeable, for it is a fairly pure
organic chemical body, which burns in the flame completely to carbon
dioxide and water, exactly as acetylene itself does. If the acetylene is
merely compressed into porous matter without acetone, the gas burnt is
acetylene simply; but per unit of volume or weight the cylinders will not
be capable of developing so much light.
In the United States, at least one railway system (The Great Northern)
has a number of its passenger coaches lighted by means of plain acetylene
carried in a state of compression in cylinders without porous matter.
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