___________________________________________________________________ | | | | | | | Nominal | Best | Duty. Candles | | Burner. | Consumption.| Pressure. | per cubic foot. | |_______________________|_____________|__________ |_________________| | | | | | | | Litres. | Inches. | | | Twin . . . . | 10 | 2.76 | 21.2 | | " . . . . | 20 | 2.76 | 23.5 | | " . . . . | 25 | 3.94 | 30.2 | | " . . . . | 30 | 3.94-4.33 | 44.8 | | ", (pair of flames) | 35 | 3.55-3.94 | 45.6 | | Bray's "Manchester" | 6 | 1.97 | 18.8 | | " | 20 | 1.97 | 35.6 | | " | 40 | 2.36 | 42.1 | | Rat-tail . . . | 5 | 5.5 | 21.9 | | " . . . | 8 | 4.73 | 25.0 | | Slit or batswing . | 30 | 1.97-2.36 | 37.0 | |_______________________|_____________|___________|_________________| Granjon has concluded from his investigations that the Manchester or fish-tail burners are economical when they consume 0.7 cubic foot per hour and when the pressure is between 2 and 2.4 inches. When these burners are used at the pressure most suitable for twin burners their consumption is about one-third greater than that of the latter per candle-hour. The 25 to 35 litres-per-hour twin burners should be used at a pressure higher by about 1 inch than the 10 to 20 litres-per-hour twin burners. At the present time, when the average burner has a smaller hourly consumption than 1 foot per hour, it is customary in Germany to quote the mean illuminating value of acetylene in self-luminous burners as being 1 Hefner unit per 0.70 litre, which, taking 1 Hefner unit = 0.913 English candle 1 English candle = 1.095 Hefner units, works out to an efficiency of 37 candles per foot in burners probably consuming between 0.5 and 0.7 foot per hour. Even when allowance is made for the difficulties in determining illuminating power, especially when different photometers, different standards of light, and different observers are concerned, it will be seen that these results are too irregular to be altogether trustworthy, and that much more work must be done on this subject before the economy of the acetylene flame can be appraised with exactitude. However, as certain fixed data are necessary, the authors have studied those and other determinations, rejecting some extreme figures, and averaging the remainder; whence it appears that on an average twin-injector burners of different sizes should yield light somewhat as follows: