350
rified by means of heratol, and finally delivered to a burner composed of thirty- seven small tubes, which raises to incandescence a mantle 55 millimetres in diameter at its base. At a pressure of 7.77 inches of water, the burner passes 3.9 cubic feet of acetylene per hour, and at a pressure of 49.2 inches (the head actually used) it consumes 20.06 cubic feet per hour. As shown by the following table, such increment of gas pressure raises the specific intensity of the light, _i.e._, the illuminating power per unit of incandescent surface, but it does not appreciably raise the duty or economy of the gas. Manifestly, in terms of duty alone, a pressure of 23.6 inches of water-column is as advantageous as the higher Chassiron figures; but since intensity of light is an important matter in a lighthouse, it is found better on the whole to work the generators at a pressure of 49.2 inches. In studying these figures referring to the French lighthouse, it is interesting to bear in mind that when ordinary six-wick petroleum oil burners wore used in the same place, the specific intensity of the light developed was 75 candle-power per square inch, and when that plant was abandoned in favour of an oil-gas apparatus, the incandescent burner yielded 161 candle-power per square inch; substitution of incandescent acetylene under pressure has doubled the brilliancy of the light.
___________________________________________________________ | | | | | | Duty. | Intensity. | | Pressure in Inches. | Candle-power per | Candle-power per | | | Cubic Foot. | Square Inch. | |_____________________|__________________|__________________| | | | | | 7.77 | 105.5 | 126.0 | | 23.60 | 106.0 | 226.0 | | 31.50 | 110.0 | 277.0 | | 39.40 | 110.0 | 301.0 | | 47.30 | 106.0 | 317.0 | | 49.20 | 104.0 | 324.9 | | 196.80 | 110.0 | 383.0 | |_____________________|__________________|__________________|
When tested in modern burners consuming between 12 and 18 litres per hour at a pressure of 100 millimetres (4 inches), some special forms of incandes