A lowering of the upper limit of explosibility is also produced by the
presence of the acetone which remains in acetylene when obtained from a
cylinder holding the compressed gas (_cf._ Chapter XI.). According
to Wolff and Caro such gas usually carries with it from 30 to 60 grammes
of acetone vapour per cubic metre, _i.e._, 1.27 grammes per cubic
foot on an average; and this amount reduces the upper limit of
explosibility by about 16 per cent., so that to this extent the gas
behaves more smoothly in an incandescent burner of imperfect design.
Lepinay has described some experiments on the comparative technical value
of ordinary acetylene, carburetted acetylene, denatured alcohol and
petroleum spirit as fuels for small explosion engines. One particular
motor of 3 (French) h.p. consumed 1150 grammes of petroleum spirit per
hour at full load; but when it was supplied with carburetted acetylene
its consumption fell to 150 litres of acetylene and 700 grammes of spirit
(specific gravity 0.680). A 1-1/4 h.p. engine running light required 48
grammes of 90 per cent. alcohol per horse-power-hour and 66 litres of
acetylene; at full load it took 220 grammes of alcohol and 110 litres of
acetylene.
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