Acetylene, the Principles of Its Generation and Use | Page 8

expense involved in burning fancy-priced oils will not be
considered here.
The efficiency (_i.e._, the light yielded per pint or other unit volume
consumed) of oil-lamps varies greatly, and, speaking broadly, increases
with the power of the lamp. But as large or high-power lamps are not

needed throughout a house, it is fairer to assume that the light
obtainable from oil in ordinary household use is the mean of that
afforded by large and that afforded by small lamps. A large oil-lamp as
commonly used in country houses will give a light of about 20 candle-
power, while a convenient small lamp will give a light of not more than
about 5 candle-power. The large lamp will burn about 55 hours for
every gallon of oil consumed, or give an illuminating duty of about
1100 candle-hours (_i.e._, the product of candle-power by
burning-hours) per gallon. The small lamp, on the other hand, will burn
about 140 hours for every gallon of oil consumed, or give an
illuminating duty of about 700 candle-hours per gallon. Actually large
lamps would in most country houses be used only in the entrance hall,
living-rooms, and kitchen, while passages and minor rooms on the
lower floors would be lighted by small lamps. Hence, making due
allowance for the lower rate of consumption of the small lamps, it will
be seen that, given equal numbers of large and small lamps in use, the
mean illuminating duty of a gallon of oil as burnt in country houses
will be 987, or, in round figures, 990 candle-hours. Usually candles are
used in the bedrooms of country houses where the lower floors are
lighted by means of petroleum lamps; but when acetylene is installed in
such a house it will frequently be adopted in the principal bed- and
dressing-rooms as well as in the living-rooms, as, unless candles are
employed very lavishly, they are really totally inadequate to meet the
reasonable demands for light of, _e.g._, a lady dressing for dinner.
Where acetylene displaces candles as well as lamps in a country house,
it is necessary, in comparing the cost of the new illuminant with that of
the candles and oil, to bear in mind the superior degree of illumination
which is secured in all rooms, at least where candles were formerly
used.
In regard to exhaustion and vitiation of the air, and to heat evolved,
self-luminous petroleum lamps stand on much the same footing as
coal-gas when the latter is burned in flat-flame burners, if the
comparison is based on a given yield of light. A large lamp, owing to
its higher illuminating efficiency, is better in this respect than a small
one-- light for light, it is more hygienic than ordinary flat-flame
coal-gas burners, while a small lamp is less hygienic. It will therefore
be understood at once, from what has already been said about the

superiority on hygienic grounds of acetylene to flat-flame coal-gas
lighting, that acetylene is in this respect far superior to petroleum lamps.
The degree of its superiority is indicated more precisely by the figures
quoted in the tabular statement which concludes this chapter.
Before giving the tabular statement, however, it is necessary to say a
few words in regard to one method of lighting which, may possibly
develop into a more serious competitor with acetylene for the lighting
of the better class of country house than any of the illuminating agents
and modes of lighting so far referred to. The method in question is
lighting by so-called air-gas used for raising mantles to incandescence
in upturned or inverted burners of the Welsbach-Kern type. "Air-gas" is
ordinary atmospheric air, more or less completely saturated with the
vapour of some highly volatile hydrocarbon. The hydrocarbons
practically applied have so far been only "petroleum spirit" or
"carburine," and "benzol." "Petroleum spirit" or "carburine" consists of
the more highly volatile portion of petroleum, which is removed by
distillation before the kerosene or burning oil is recovered from the
crude oil. Several grades of this highly volatile petroleum distillate are
distinguished in commerce; they differ in the temperature at which they
begin to distil and the range of temperature covered by their distillation,
and, speaking more generally, in their degree of volatility, uniformity,
and density. If the petroleum distillate is sufficiently volatile and fairly
uniform in character, good air-gas may be produced merely by allowing
air to pass over an extended surface of the liquid. The vapour of the
petroleum spirit is of greater density than air, and hence, if the course
of the air-gas is downward from the apparatus at which it is produced,
the flow of air into the apparatus and over the surface of the spirit will
be automatically maintained by the "pull" of the descending air-gas
when once the flow has been started until the