It is essential that the apertures for the emission of the gas of the argand gas lamp, be perfectly round and of an uniform size, without this condition the flame of the lamp is ragged, and not well defined.
Fig. 15, [plate III.], exhibits a swing bracket, furnished with a cockspur burner. The burner consists of a hollow flattened globe, about half an inch in diameter, pierced laterally with three or more holes, of about 1⁄30 of an inch in diameter; out of these holes the gas flame issues in streams as shown in the sketch. With this burner the combustion of the gas is imperfect, and it is a wasteful mode of burning coal gas. The surrounding holes of the cockspur burner, was it not for the upward current of air, would give flames radiating in straight lines from the centre of the burner, but the ascending current of heated air, causes them to curve upwards like the spur of a game cock, and hence the name cockspur burner.
If the gas be made to burn from a series of holes made in the lateral circumference of a hollow flat cylinder, it will produce a circular horizontal series of flames curving upwards.
Fig. 12. [plate V.], is called a bat’s wing burner; it consists of a small pear-shaped steel burner, about 1⁄16 of an inch in diameter, having a perpendicular slit at its upper extremity, about 1⁄40 of an inch in diameter. This burner exhibits a tulip-shaped flame, as shown fig. 13, [plate V.], it is well adapted for street gas lamps.
The stop-cock for admitting gas into gas burners should always be placed at least six inches from the burner. The stop-cock in the brackets, fig. 8, or 9, [plate V.], is placed at a. Pendant gas lamps, into which the gas is conveyed from a pipe above, through the ceiling, should be provided with a mercurial joint, or ball and socket joint. The former contrivance is preferable, because it can never leak;[51] but the latter requires occasional repairs. Fig. 14, [plate III.], shews the mercurial joint. a, is the pipe which brings the gas; it terminates in a sheet iron cup open at bottom, but closed air tight at the top; this cup is inverted into a small iron bason, containing mercury. D the iron tube which communicates with the gas lamp or burner, and the upper extremity of which projects above the surface of the mercury in the iron bason, whilst the other extremity proceeds to the burners or lamps.
[51] This contrivance has been adopted throughout the fitting up of the gas lights at the Royal Mint.
Swing bracket burners, fig. 13, [plate III.], should have the axis of motion at the joints A, A, A, perforated at right angles to each other, so as to admit the moveable joints at A, to be left open, without obstructing the passage of the gas when the bracket assumes different angular positions. All swing brackets ought to have a double, and not a single joint, because the latter soon wears oval in the two opposite edges; this is prevented by the double joint having an uniform bearing at top and bottom, it therefore can never leak.
Fig. 11, [plate VI.], exhibits the arrangement usually adopted for a pendant perpendicular sliding lamp, or chandelier, which requires to be raised or depressed. This contrivance is convenient for lighting theatres, or public buildings, by means of a large central gas light chandelier, that may be raised or depressed at pleasure.
The gas enters into the tube D, which is firmly fixed in the ceiling, as shown in the sketch; it passes through a hole near E, into a smaller tube j, which slides perpendicularly within the tube D. This sliding tube is made air tight by means of two stuffing boxes filled with oil, placed near B, and C. The sliding tube j, together with the chandelier suspended to it, is counter-balanced by a weight concealed in a box W, connected with pullies in the usual manner, as shown in the sketch, so that the chandelier may be raised or lowered at pleasure.