The gas-tight gallery used for testing the lamps, consists of a rectangular conduit (Fig. 2, [Plate X]), having sheet-steel sides, 6 mm. thick and 433 mm. wide, the top and bottom being of channel iron. The gallery rests on two steel trestles, and to one end is attached a No. 5 Koerting exhauster, capable of aspirating 50 cu. m. per min., under a pressure of 500 mm. of water, with the necessary valve, steam separator, etc. The mouth of the exhauster passes through the wall of the building and discharges into the open air.
Besides the main horizontal conduit, there are two secondary conduits connected by a short horizontal length, and the whole is put together so that the safety lamp under test may be placed in a current of air, or of air and gas, which strikes it horizontally, vertically upward or downward, or at an angle of 45° ([Fig. 3]). The path of the current is determined by detachable sheet-steel doors.
There are five double observing windows of plate glass, which open on hinges. The size of each window is 7½ by 3 in.; the inner glass is ¼ in. thick and the outer one, ½ in. thick. These glasses are separated by a space of ¼ in. The upper conduit has four safety doors along the top, each of the inclined conduits has one safety door, and the walls and windows are provided with rubber gaskets or asbestos packing, to make them gas-tight. The cross-sectional area of the conduit is 434 sq. cm.
The air inlet consists of 36 perforations, 22 mm. in diameter, in a bronze plate or diaphragm. The object of this diaphragm is to produce pressure in the conduit before the mixing boxes, and permit the measuring of the velocity of the current. The air-current, after
passing through the holes, enters the mixer, a cast-steel box traversed by 36 copper tubes, each perforated by 12 openings, 3 mm. in diameter, arranged in a spiral along its length and equally spaced. The total cross-sectional area of the tubes is 137 sq. cm.
The explosive gas enters the interior of the box around the tubes through large pipes, each 90 mm. in diameter, passes thence through the 432 openings in the copper tubes, and mixes thoroughly with the air flowing through these tubes. The current through the apparatus is induced by the exhauster, and its course is determined by the position of the doors.
The gallery can be controlled so as to provide rapidly and easily a current of known velocity and known percentage of methane. In the explosive current of gas and air, safety lamps of any size or design can be tested under conditions simulating those found occasionally in mines, air-currents containing methane in dangerous proportions striking the lamps at different angles, and the relative safety of the various types of lamps under such conditions can be determined. In this gallery it is also possible to test lighting devices either in a quiet atmosphere or in a moving current, and, by subjecting the lamps to air containing known percentages of methane, it is possible to acquaint the user with the appearance of the flame caps.