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| | | | | |
| Size of Burner | Pressure | Cubic Feet | Light in | Candles per |
| in Litres. | Inches. | per Hour. | Candles. | Cubic Feet. |
|________________|__________|____________|__________|_____________|
| | | | | |
| 55 | 39.4 | 1.94 | 220 | 113.4 |
| 100 | 39.4 | 3.53 | 430 | 121.8 |
| 180 | 39.4 | 6.35 | 820 | 129.1 |
| 260 | 27.6 | 9.18 | 1300 | 141.6 |
|________________|__________|____________|__________|_____________|
High-power burners such as these are only fit for special purposes, such as lighthouse illumination, or optical lantern work, &c.; and they naturally require mantles of considerably greater tenacity than those intended for employment with coal-gas. Nevertheless, suitable mantles can be, and are being, made, and by their aid the illuminating duty of acetylene can be raised from the 30 odd candles per foot of the common 0.5-foot self-luminous jet to 140 candles or more per foot, which is a gain in efficiency of 367 per cent., or, neglecting upkeep and sundries and considering only the gas consumed, an economy of nearly 79 per cent.
In 1902, working apparently with acetylene dissolved under pressure in acetone (cf. Chapter XI.), Lewes obtained the annexed results with the incandescent gas:
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| | | | |
| Pressure. | Cubic Feet | Candle Power | Candles per |
| Inches. | per Hour. | Developed. | Cubic Foot. |
|___________|_____________|______________|______________|
| | | | |
| 8 | 0.883 | 65 | 73.6 |
| 9 | 0.94 | 72 | 76.0 |
| 10 | 1.00 | 146 | 146.0 |
| 12 | 1.06 | 150 | 141.2 |
| 15 | 1.25 | 150 | 120.0 |
| 20 | 1.33 | 166 | 124.8 |
| 25 | 1.50 | 186 | 123.3 |
| 40 | 2.12 | 257 | 121.2 |
|___________|_____________|______________|______________|
It will be seen that although the total candle-power developed increases with the pressure, the duty of the burner attained a maximum at a pressure of 10 inches. This is presumably due to the fact either that the same burner was used throughout the tests, and was only intended to work at a pressure of 10 inches or thereabouts, or that the larger burners were not so well constructed as the smaller ones. Other investigators have not given this maximum of duty with a medium-sized or medium-driven burner; but Lewes has observed a similar phenomenon in the case of 0.7 to 0.8 cubic foot self-luminous jets.
Figures, however, which seem to show that the duty of incandescent acetylene does not always rise with the size of the burner or with the pressure at which the gas is delivered to it, have been published in connexion with the installation at the French lighthouse at Chassiron, the northern point of the Island of Oléron. Here the acetylene is generated in hand-fed carbide-to-water generators so constructed as to give any pressure up to nearly 200 inches of water column; purified 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.
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| | | |
| | 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 incandescent mantles constructed of ramie fibre, which in certain respects appears to be better suited than cotton for use with acetylene, have shown the following degree of loss in illuminating power after prolonged employment (Caro):
_Luminosity in Hefner Units._
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| | | | | |
| Mantle. | New. | After | After | After |
| | | 100 Hours. | 200 Hours. | 400 Hours. |
|_________|_______|____________|____________|____________|
| | | | | |
| No. 1. | 53.2 | 51.8 | 50.6 | 49.8 |
| No. 2. | 76.3 | 75.8 | 73.4 | 72.2 |
| No. 3. | 73.1 | 72.5 | 70.1 | 68.6 |
|_________|_______|____________|____________|____________|