The latter method is what is generally known as i the incandescent gas lighting system. The original developments in gas lighting were made on the first of these principles. The bat swing or fishtail flame was produced by re leasing the gas through a narrow slit, and its illumination was produced by the incandescence of the solid particles of carbon derived from the decomposing gas in the flame. The Argand gas burner is a modification of the old Argand oil burner, and consists of a ring of small open ings arranged near enough together so that the gas flame is in the form of a continuous cylinder, admitting air to the inside and out side of the cylinder. The Siemens-Lungren system, known as the Regenerative system, con sisted in applying to the burner gas and air which has been preheated. Professor Bunsen, professor of chemistry in Heidelberg, designed a burner to produce a non-luminous flame with complete combustion and to give the maximum heating effect of the gas. This was accom plished by so constructing a burner that it will carry in and mix with the gas a limited amount of air before it reaches the point of combustion. The additional air necessary to produce com plete combustion is drawn from the atmosphere surrounding the flame. This type is known as the Bunsen burner.
The experiments of Henry Drummond in 1826, in which he placed a solid stick of lime in the oxy-hydrogen flame, was the first sys tematic attempt at the development of what is now known as the incandescent gas lighting system. The Drummond, or lime-light, was until recently in general use for the production of very high power lights, especially in theatres and for stereopticon practice, etc. This system, however, was not applicable to the ordinary con ditions of gas lighting. A modification of the Drummond light was made by Tessie du Motay, in which he substituted coal gas for the hydro gen in the ordinary Drummond oxy-hydrogen flame. A burner exhibited at the Crystal Palace Electric and Gas Exposition in 1883, by Lewis, was constructed with a platinum mantle sus pended over the flame, and designed to pro duce a high incandescence. This mantle, how ever, was unsuccessful, owing to the fact that it rapidly deteriorated by the reducing action of the gas. This burner was designed to operate with compressed air. Clamond about the same time introduced a burner similar to the Bunsen type, in which he placed a mantle made of threads of magnesia. He also introduced an in verted pattern or burner in which a basket or mantle was made of magnesia threads held in a platinum basket. This burner, like the Lewis burner, was operated by compressed air, and was claimed to produce 4% candles per foot of gas consumed, with a life of from 50 to 60 hours. Mantles in modification of the Clamond type were produced by C. B. Harris, in which he molded a refractory material into sheets, pressed into the proper shape and perforated in any desired pattern. Attempts have also been made to make a mantle of asbestos or similar non-combustible material, and saturate this with a substance gilYing high incandescence.
The first commercially successful results ac complished in the field of incandescent gas lighting were made by Dr. Carl Auer von Wels bach of Vienna. Welsbach's work in this field began in 1880, in Bunsen's laboratory in Heidel berg, where he was studying the tare earths from a standpoint of pure chemistry. His at tention was centred on the oxide of erbium. To produce a continuous light for spectro scopic study he satuated a cotton fabric with a solution of erbium, and after burning out the cotton suspended the residual ash in the flame. This produced an intense green light. The idea occurred to Welsbach to utilize this particular method for producing an ash fabric of incan descing material in the ordinary Bunsen gas flame. When this plan was communicated to Bunsen he replied: "It appears most improbable that the oxides could be• made to adhere." Welsbach, however, continued his experiments, choosing not erbium oxide, but oxides which would give a high white incandescence when heated. His researches led him through the
entire field of the elements having stable oxides, and certain oxides of the so-called rare earths were found to give the most promising results. The oxide of lanthanum made a perfect mantle in appearance and produced an intense glow in the colorless flame of a Bunsen burner, but the mantle was found to crumble to a powder within a short time. Welsbach then began ex periments with a view of mixing something with a lanthanum which would produce a non slaking body. In 1886 what is known as the lanthanum-zirconium mantle was introduced. This mantle was made by saturating a closely knit cotton fabric with the proper mixture of zirconium and lanthanum nitrates, burning out the cotton and leaving a network of ash com posed of the oxides of zirconium and lanthanum. These mantles gave 12 candle power per cubic foot of gas consumed, and lasted several hun dred hours. To quote Welsbach : "The sum of all these results appeared encouraging, and I was audacious enough to pronounce the endeavors of the gas engineers to increase the illuminating power of the open flame, as useless and vain ; for it was evident that it was much more eco nomical to renounce the lighting power of the open flame and to transform it into a Bunsen flame, and to get those substances to incandesce in the very hot part of that Bunsen flame, by which method two or three times the amount of light of an open flame could be attained." The invention was now called to the atten tion of the public, and Welsbach delivered numerous lectures before the press representa tives. The invention was named the Incan descent Gas Light by Mr. Sceps, editor of the Neue Wiener riigeblatier. The announcement of the Welsbach mantle was received with vari ous comment, and many prominent engineers re fused to take the matter seriously. Welsbach's confidence, however, was not shaken, and com panies were formed for the development of the industry and the manufacture of the lighting fluid from the rare earths. The services of Dr. Ludwig Haitinger. an able chemical engi neer, were added to those of Dr. Auer in the development of this work. The increased effi ciency of this method of lighting, however, was not what had been expected, and the public re fused to take it up. The mantle rapidly de teriorated and required to be rejuvenated. At that time it must also be understood that these mantles were very fragile and in the early stages of the work they were delivered in the city of Vienna by a boy carrying one in each hand, as they would not bear the ordinary han dling in transportation. The usual skepticism of the public in regard to new inventions pre vailed, and the commercial failure of this enter prise seemed imminent. The Vienna factory was closed and the plant and laboratory sold. The American factory, under the direction of Waldron Shapleigh, was still producing with some success the lanthanum-zirconium mantle. Welsbach, however, was not discouraged by these drawbacks, and devoted his entire atten tion to the development and improvement of the mantle. In the early nineties he went before the public with an entirely new mantle, which was composed of 99 per cent thorium oxide and 1 per cent cerium oxide. This mantle gave 24 candles per cubic foot of gas consumed. The present system of manufacture of mantles is entirely in accordance with this last invention of Welsbach's, which consists in saturating cot ton fabric with the proper mixture of the ni trates of thorium and cerium, burning out the cotton fabric and tempering the mantle. It is then coated with collodion and packed for the market. Various improvements have been made in the Bunsen burner and a large number of designs are now on the market ; but the general Bunsen principle is strictly adhered to and the present incandescent gas light is pro duced by applying the incandescing material to the colorless Bunsen burner flame.