SAFETY LAMP TESTING GALLERY]

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,