Aside from the usual analysis of explosives for the Isthmian Canal Commission, special tests are made to determine the liability of the explosive to exude nitro-glycerine, and to deteriorate in unfavorable 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. Hydrogen gases 0 Carbon dioxide 0.1 Oxygen 0 Heavy hydrocarbons 0 Carbon monoxide 0 Methane 81.8 Ethane 16.8 Nitrogen 1.3 The volume of gas used is measured by an accurate test meter reading to one-twentieth of a cubic foot. The required amount is admitted near the bottom, to one or more of the 20-ft. divisions of the gallery, from a 2-in. pipe, 14 ft. long. The pipe has perforations arranged so that an equal flow of gas is maintained from each unit length. Each 20-ft. division of the gallery is further equipped with an exterior circulating system, as shown by Fig. 1, thus providing an efficient method of mixing the gas with the air. For the first division this circulating system is stationary, a portion of the piping being equipped with heating coils for maintaining a constant temperature. The other divisions have a common circulating system mounted on a truck which may be used on any of these divisions. Valves are provided for isolating the fan so that a possible explosion will not injure it.