The bat's-wing or slit burner, Fig. 106, has a hemispherical tip with a narrow vertical slit from which the gas spreads out in a thin, flat sheet, giving a wide and rather low flame resembling in shape the wing of a bat, from which it is named.
The union-jet or fish-tail burner, Fig. 107, consists of a flat tip slightly depressed or concaved in the center, with two small holes drilled, as shown in Fig. 108. Two jets of equal size issue from these holes, and, by impinging upon each other, produce, at right angles to the alignment of the holes, a flat flame longer and narrower in shape than the bat's-wing, and not unlike the tail of a fish. Neither of these burners requires a chimney, but the flames are usually encased with glass globes. They are not well suited for use with globes, however, since when one of the jets becomes choked, as it frequently does, the other is likely to crack the glass.
The Argand burner, Fig. 109, consists of a hollow ring of metal or lava, connected with the gas tube, and perforated on its upper Furface with a series of fine holes, from which the gas is sues, forming a round flame. This burner re quires a glass or mica chimney. As an intense heat of combustion tends to increase the brilliancy of the flame, it is desirable that the burner tips shall be of a material that will cool the flame as little as kossible. On this account, metal tips are inferior to those made of some non-conduct ing material, such as lava, adamant, enamel, etc. Metal tips are also objectionable because they cor rode rapidly, and thus obstruct the passage of the gas. Fig. 110 shows a lava tip for a bat's-wing burner. Burner tips should be cleaned occasionally, but care should be taken not to enlarge the holes.
By introducing the Bunsen principle, incandescent burners give good service with coal gas. In the incandescent burner, the heat of the flame is applied in raising to incandescence some foreign mater ial, such as a basket of magnesium or platinum wires, or a funnel shaped asbestos wick, or a mantle treated with sulphate of zir conium and other chemical compounds. A burner of this kind is shown in Fig. 111, in which the mantle can be seen supported over the gas flame by a wire at the side. Fig. 112 shows another form
of this burner, in which a chimney and shade are used in place of a globe. Burners of this kind give a very brilliant white light when used with natural or water gas. Natural gases and the so-called water gas are deficient in carbon; and, when they are used for lighting purposes, the light is produced by a burner with a mantle brought to a state of incandescence by the heat of the flame. The mantle, however, is very fragile, and is likely to lose its property of incan descence when exposed to an atmosphere containing much dust.
The Bunsen burner, shown in Fig. 113, is a form much used for laboratory work. It burns with a bluish flame, and gives an intense heat without smoke or soot. The gas, before ignition, is mixed with a certain quantity of air, the pro portions of gas and air being regu lated by the thumb-screw at the bottom, and by screwing the outer tube up or down, thus admitting a greater or less quantity of air at the openings indicated by the arrows.
This same principle is utilized in a burner for brazing, the general form of which is shown in Fig. 114. A flame of this kind will easily melt brass in the open air.
It is of great importance that gas keys on fixtures should be per fectly tight. It is rare to find a house piped for gas where the pressure test could be successfully applied without first removing the fixtures, as the joints of folding brackets, extension pendants, stop cocks, etc., are usually found to leak more than the piping. The old fashioned all-around cock without check-pin should never be allowed under any conditions; only those provided with stop-pins are safe. Various forms of cocks with stop-pins are shown in Figs. 115, 116, and 117. All key joints should be examined and tightened up occasionally to prevent them becoming seriously loose and leaky. Poor illumination is frequently caused by ill-designed or poorly constructed brackets or gasoliers. Gas fixtures, almost without exception, are designed solely from an artistic standpoint, without due regard to the proper conditions for obtaining the best illumination.