In each end of the box is an opening 1 ft. square, over which may be
placed a paper diaphragm held by skeleton doors, the purpose of which
is to confine the gas in such a manner that, should an explosion occur,
no damage would be done. In the front of the box are two plate-glass
observing windows, 2⅝ by 5½ in. In the side of the box, between the
two windows, is a ⅜-in. hole, which can be closed by a tap-screw,
through which samples for chemical analysis are drawn.

The gasometer consists of two iron cans, the lower one being open at
the top and filled with water and the upper one open at the bottom and
suspended by a counterweight. The latter has attached to its upper
surface a scale which moves with it, thereby measuring the amount of
gas in the holder. A two-way cock permits the admission of gas into the
gasometer and thence into the testing box.

_Gas-and-Dust Gallery No. 2._--This gallery is constructed of sheet
steel and is similar to Gallery No. 1, the length, however, being only
30 ft. and the diameter 10 ft. It rests on a concrete foundation (Fig.
3, Plate X). Diaphragms can be placed across either extremity, or at
various sections, to confine the mixtures of gas and air in which the
tests are made. The admission of gas is controlled by pipes and valves,
and the gas and air can be stirred or mixed by a fan, as described for
Gallery No. 1, and as shown by Fig. 1.

Gallery No. 2 is used for investigating the effect of flames of various
lamps, of electric currents, motors, and coal-cutting machines, in the
presence of known mixtures of explosive gas and air. It is also used for
testing the length of flame of safety lamps in still air carrying
various proportions of methane, and, for this purpose, is more