Fig. 113. A Bunsen Burner..
Fig. 114. Gas Burner for Brazing..
Fig. 115. Single Gas-Cock With Stop-Pin..
Fig. 116. Double Gas-Cock with Stop-Pins..
Fig. 117. Elbow Gas-Cock with Stop-Pin..
Fig. 118. Common Form of- Gas-Bracket..
Fig. 119. Two-Swing Extension Gas-Bracket.
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 proportions of gas and air being regulated 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.
Fixtures. It is important that gas keys on fixtures should be perfectly 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, stopcocks, 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.
Fig. 120. Plain Type of Two-Burner Gasolier..
Fixtures having too many scrolls or spirals may, in the case of imperfectly purified gas, accumulate a large amount of a tarry deposit, which, in time, hardens and obstruct the passages. Another fault is the use of very small tubing for the fixtures. Common forms of brackets are shown in Figs. 118 and 119, the latter being a two-swing extension bracket.
Fig. 121. Ornamental Type of Two-Burner Gasoller..
Fig. 122. Gasolfer for Hall or Corridor..
There are an endless variety of gasoliers used, depending upon the kind of building, the finish of the room, and the number of lights required. Figs. 120,121, and 122 show common forms for dwelling houses the type shown in Fig. 122 being used for halls and corridors. The keys should be at the lowest point, as in Figs. 121 and 122, to facilitate removing any condensation that may take place and find its way to the fixture.
Fig. 123. Simple Form of Gas Plate with Three.
Next to the burner, the shape of the globe or shade surrounding the flame affects the illuminating power of the light. In order to obtain the best results, the flow of air to the flame must be steady and uniform. Where the air supply is insufficient, the flame is likely to smoke; on the other hand, too strong a current of air causes the light to flicker and become dim through cooling.
Globes with openings too small at the bottom, should not be used. Four inches at the bottom should be the smallest opening used for an ordinary size burner. All glass globes absorb more or less light, the loss varying from 10 per cent for clear glass, to 70 per cent or more for opal, ground, colored, or painted globes. Clear glass is therefore much more economical, although, where softness of light is especially desired, the use of opal or ground globes is made necessary.
Illumination. Illumination is a subject so broad and complex that a fairly thorough consideration of light distribution for different purposes would alone require a volume. A few pertinent remarks tending to aid in approximating the location and power of lamps so as to get reasonably accurate results in ordinary work will not, however, be out of place here.
The unit of illumination is the candle-foot - the power of one standard candle at a distance of one foot from its flame. The intensity of illumination varies inversely as the square of the distance from the source. Therefore we see that one candle-power at one foot from the source gives only one-fourth of a candle-power over an equal amount of surface placed two feet from the source.
The candle-foot illumination of any point, for any bare light nominated can be approximated by squaring the distance from burner to the point selected, using the square as a denominator and 1 as the numerator of a common fraction (reduced to a decimal if preferred) multiplying by the candle-power of the burner to be used and then adding the illumination due to reflection. The result will be near the candle-feet illumination at the selected point.