GAS LIGHTING, High Pressure. High pressure as lighting represents the most effi cient application of the energy in illuminating gas to the production of light, and is the highest development of the use of the Bunsen burner in connection with the Welsbach incandescent mantle. The principle involved is simply the production of high flame temperature within or on a mantle of highly refractory and radio active elements by the complete combustion of gas in a concentrated flame volume. This prin ciple was first demonstrated before the Phila delphia Chemical Society in 1801 by Dr. Robert Hare, by exhibiting the effect of concentrating the oxy-hydrogen flame on a refractory sub stance. The term Thigh pressures is recognized as distinguishing it from ordinary incandes cent gas lighting, because of the fact that the greatest number of lighting appliances coming within this class depend on the gas being sup plied at higher pressures than are common in the ordinary distribution of illuminating gas from the works to the consumer. There are other types of units, however, of equally high luminous efficiency which come within this class, bnt which use the gas at the ordinary pressures, complete and high temperature com bustion of which is effected by supplying the air at pressures ranging from one to two pounds above the atmosphere. These types have not met with such general favor as the other, on account of requiring a double pipe line system, one to carry the gas and the other to carry the air under pressure, and also because of the greater amount of compression needed to sup ply the large quantities of air used.
The lamps of the first type mentioned use gas at two to three pounds pressure per square inch (54 to 81 inches water column). The ordinary pressures at which gas is dis tributed range from one to four inches water column. These lamps use the energy of the gas under pressure flowing from a small orifice at high velocity to entrain from four to six volumes of air per volume of gas by simple injector action into the Bunsen tube and be fore being burned the gas and air are thor oughly mixed and pre-heated in the extending chamber from the Bunsen tube. At first high
pressure lamps were designed to use the up right mantle, but later developments of the in verted mantle recommend it particularly for this class of lighting, because of the fact that the best incandescent results are obtained by having the mantle conform as closely to the flame as is possible, in order to have all its fibres in the zone of the highest temperature. Inverted mantles for high pressure units are applied to the burners ir a soft state, so that in burning off and hardening they assume the exact form of the flame on which they are used. This factor is one of the important elements in the luminous efficiency of high pressure units. For low pressure lighting mantles are furnished which have been shaped and hardened in a pressure Bunsen furnace to a length approximating the size of a low pres sure gas flame. It is impossible with gas at low or ordinary distribution pressure to com pletely burn out and properly shape the mantle fabric.
The increase in efficiency of gas lighting by the use of high pressure gas can be seen from the following comparisons: The candle-power values of the limits given above are horizontal or maximum candle power intensities. In the utilization of the heat energy in gas for the production of light, which is really the proper measure of efficiency and energy transferred, we have the following: Flat flame burner, coal gas: 200 British thermal units per candle power. Flat flame burner, water gas: 150 British thermal units per candle power. Low pressure incandescent Welsbach burners: 35 to 30 British thermal units per candle power.
High pressure gas units: 15 to 10 British thermal units per candle power.
From this it is seen that with high pressure gas the ratio of energy input in the form of heat to light output measured as candle power is 20 times that of flat flame gas lighting and three times more efficient than Welsbach burn ers using gas at low pressures.