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

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 outlet for the air-gas is stopped or the spirit in the apparatus is exhausted. Hence, if the apparatus for saturating air with the vapour of the light petroleum is placed well above all the points at which the air-gas is to be burnt-- _e.g._, on the roof of the house--the production of the air-gas may by simple devices become automatic, and the only attention the apparatus will require will be the replenishing of its reservoir from time to time with light petroleum. But a number of precautions are required to make this simple process operate without interruption or difficulty. For instance, the evaporation of the spirit must not be so rapid relatively to its total bulk as to lower its temperature, and thereby that of