DUTY OF INCANDESCENT ACETYLENE BURNERS.--Granting that the petty troubles and expenses incidental to incandescent lighting are not considered prohibitive--and in careful hands they are not really serious-- and that mantles suitable for acetylene are employed, the gas may be rendered considerably cheaper to use per unit of light evolved by consuming it in incandescent burners. In Chapter VIII. it was shown that the modern self-luminous, l/2-foot acetylene burner emits a light of about 1.27 standard English candles per litre-hour. A large number of incandescent burners, of German and French construction, consuming from 7.0 to 22.2 litres per hour at pressures ranging between 60 and 120 millimetres have been examined by Caro, who has found them to give lights of from 10.8 to 104.5 Hefner units, and efficiencies of from 2.40 to 5.50 units per litre-hour. Averaging his results, it may be said that incandescent burners consuming from 10 to 20 litres per hour at pressures of 80 or 100 millimetres yield a light of 4.0 Hefner units per litre- hour. Expressed in English terms, incandescent acetylene burners consuming 0.5 cubic foot per hour at a pressure of 3 or 4 inches give the duties shown in the following table, which may advantageously be compared with that printed in Chapter VIII., page 239, for the self-luminous gas: ILLUMINATING POWER OF INCANDESCENT ACETYLENE. HALF-FOOT BURNERS. 1 litre = 3.65 candles | 1 candle = 0.274 litre. 1 cubic foot = 103.40 candles. | 1 candle = 0.0097 cubic foot. A number of tests of the Güntner or Schimek incandescent burners of the 10 and 15 litres-per-hour sizes, made by one of the authors in 1906, gave the following average results when tested at a pressure of 4 inches: _________________________________________________________________ | | | | | | Nominal size | Rate of Consumption per | Light in | Duty | | of Burner. | Hour | Candles | Candles per | | | | | Cubic Foot | |______________|_________________________|__________|_____________| | | | | | | | Litres. | Cubic Foot | Litres | | | | 10 | 0.472 | 13.35 | 46.0 | 97.4 | | 15 | 0.663 | 18.80 | 70.0 | 105.5 | |______________|____________|____________|__________|_____________| These figures indicate that the duty increases slightly with the size of the burner. Other tests showed that the duty increased more considerably with an increase of pressure, so that mantles used, or which had been previously used, at a pressure of 5 inches gave duties of 115 to 125 candles per cubic foot.