weather conditions. These tests are necessary, because of the warm and
moist climate of the Isthmus of Panama.

_Gas and Dust Gallery No. 1._--Gallery No. 1 is cylindrical in form,
100 ft. long, and has a minimum internal diameter of 6⅓ ft. It consists
of fifteen similar sections, each 6⅔ ft. long and built up in in-and-out
courses. The first three sections, those nearest the concrete head, are
of ½-in. boiler-plate steel, the remaining twelve sections are of ⅜-in.
boiler-plate steel, and have a tensile strength of, at least, 55,000 lb.
per sq. in. Each section has one release pressure door, centrally placed
on top, equipped with a rubber bumper to prevent its destruction when
opened quickly. In use, this door may be either closed and unfastened,
closed and fastened by stud-bolts, or left open. Each section is also
equipped with one ¾-in. plate-glass window, 6 by 6 in., centrally placed
in the side of the gallery (Fig. 1, and Figs. 1 and 2, Plate VI). The
sections are held together by a lap-joint. At each lap-joint there is,
on the interior of the gallery, a 2½-in. circular, angle iron, on the
face of which a paper diaphragm may be placed and held in position by
semicircular washers, studs, and wedges. These paper diaphragms are used
to assist in confining a gas-and-air mixture.

[Illustration: Fig. 1.

EXPLOSIVES TESTING GALLERY No. 1]

Natural gas from the mains of the City of Pittsburg is used to represent
that found in the mines by actual analysis. A typical analysis of this
gas is as follows:

Volumetric Analysis of Typical Natural Gas.