The first incandescent gas mantles were of approximately conical form, suspended above the upwardly directed flame from an upright burner by means of a loop in the apex of the mantle. On account of the expansion of the mantle under heat it was impracticable to secure the bottom or "skirt° of the mantle to the burner-head, and the swaying of the skirt against the burner-head with every vibration of the lamp resulted in disintegration of the lower portion of the mantle. In 1907 the inverted mantle and burner were introduced. In this type a mantle of roughly hemispherical form was suspended below the downwardly directed flame of an inverted burner. The open end of the mantle was affixed to the burner-head and thus rigidly supported. Although the inverted mantle greatly exceeded the upright in durabil ity, the arrangement of the burner parts was unsatisfactory in that the burner being below the supporting fixture discolored the latter by the strongly heated combustion products. In 1915 an upright burner bearing inverted mantles was introduced. In this lamp was combined the strength of the inverted mantle and the structural advantages of the upwardly project ing lamp body—particularly desirable for at taching to fixtures designed for the upright open flame tips. Up to this time the develop ment of the gas lighting industry had been much restricted by the above mentioned lim itations and the lack of flexibility in the adapta tion of gas lamps resulting from these limita tions.
Almost coincidentally with the development of the upright inverted mantle lamp it was dis covered that by conserving the kinetic energy of the gas through proper design it was possible to control the gas and air mixture so com pletely that practically any structural combina tion imposed by the requirements of fixture de sign or illumination requirements may be real ized and the light yield much increased. Al though the mantles are best suspended in an inverted position, the burner may be vertically upright or inverted, horizontal or angular. By the application of these principles, incandescent gas lamps ranging from 25 to 2,500 candle power have been successfully operated, and all of the various systems of illumination — direct, indi rect and semi-indirect — successfully applied. In connection with other development, refine ments in ignition and control have been so elaborated that any desired condition of opera tion may be met.
Gas for lighting is usually distributed at a pressure of from two to three inches of water column. At these pressures the most recent incandescent gas lamps give from 28 to 30 candle power per cubic foot of gas consumed. For street and factory lighting, higher pressures are coming into use, and at a pressure of three pounds per square inch a yield of from 50 to 60 candle power per cubic foot is obtained.
The wonderful ability of Auer von Wels bach as a chemist and inventor should also be noted, from the fact that the chemicals used in the production of the mantles were very rare and almost unknown, and that he was called upon to find the raw material for the produc tion of these chemicals, and to invent proc esses for their extraction in a sufficiently pure state for use. All of this work was accom plished successfully after years of patient, pains taking endeavor. Within the past decade the decorative side of gas lighting has been all appealing. The primary idea of gas lighting was illumination, but with a desire for greater comforts and more luxuries in everyday life has come the desire for decorative effects. Globes, shades and domes are now made in many varieties. Color schemes of beauty are evolved, and artist and artisan combine to lend decorative worth to shape, color and treatment of the globe or shade, which is destined to add to the bare illumination of the gas jet or the incandescent mantle.
In 1917 the entrance of the United States into the Great War imposed radical changes upon the gas practice of the country. The entire production of benzol and toluol (the basis of the most efficient high explosives) from the by-product coke oven plants — the principal source — was under contract to the Entente Allies, and the United States government had recourse to the plants furnishing illuminating gas to obtain its own supply of these needed chemicals. Benzol and toluol are largely re sponsible for the luminosity of the open-flame gas burner, and the necessity for removing these substances from illuminating gas made the incandescent mantle almost an universal necessity wherever gas was employed for light ing. The mantle burners in use before this time were relatively expensive (when of good quality) and had been restricted to the more important uses, the open-flame burner being used for occasional and intermittent service. In many cities more than one-half of the gas used for lighting was burned in open flame tips.
In order to make the needed conversion of these less-frequently-used burners to mantle lamps without imposing undue burden upon the consumer, a small, relatively inexpensive mantle burner, of substantially the same light-giving power as the previous open-flame burner was developed. This effects a saving of about two thirds in gas consumption and permits all the toluol and benzol to be removed, from the gas without impairing its light-giving power.
Table showing efficiency of various systems of gas lighting in use at the present time: