292 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 1910. 



control. Beginning some 30 years ago, many kinds of chambers have 

 been employed, from one made of boiler iron mounted on wheels used 

 at Zwickau, Germany; an abandoned mine tunnel used at Eossitz, 

 Austria; a wooden gallery used at Frameries, Belgium; a concrete 

 gallery used at Lievin, France; to metal galleries as used at Wool- 

 wich, England, and Pittsburg, United States. This last is one of the 

 most modern of these testing galleries, it having been erected on the 

 arsenal grounds by the technologic branch of the United States Geo- 

 logical Survey in 1908, and as it was designed after careful study of 

 the characteristics of different galleries abroad it may be regarded as 

 representing the latest type of testing chamber. 



This chamber, which is styled gas and dust gallery No. 1, is shown 

 in plate 1. It consists of a cylinder 100 feet in length and 6£ feet in 

 diameter, which is built of boiler-plate steel, in five divisions, each 

 consisting of three sections 6§ feet long. The gallery is closed at one 

 end by a concrete head. The different sections of the gallery are for 

 convenience in operation numbered consecutively from 1 to 15, be- 

 ginning with the section nearest the concrete head. Sections Nos. 

 1, 2, and 3 are made of one-half inch plates, the remaining sections of 

 three-eighths inch plates, and all of steel having a tensile strength 

 of not less than 55,000 pounds to the square inch. The sections are 

 held together by lap joints, at each of which there is on the interior 

 of the gallery a ring, formed of 2^-inch angle iron, upon the face of 

 which paper diaphragms may be so secured as to partition off any 

 desired portion of the gallery at will, and thus provide a closed space 

 of any desired volume, within the capacity of the gallery, in which 

 to inclose the gas-air, coal-dust-air, or gas-coal-dust-air mixture to be 

 used in the test. 



Each section is provided with a pressure-release door placed cen- 

 trally on top, which not only provides a vent by which the gases may 

 immediately escape after the explosion, and thus acts as a safety valve 

 to prevent the destruction of the gallery, but also affords an ap- 

 proximate means of estimating the pressures developed. Each door 

 closes on a rubber gasket and is provided with a rubber bumper on its 

 back to prevent injury when thrown open violently. In use each door 

 may be left open, or closed but not fastened, or closed and fastened, as 

 seems best under the experimental conditions which obtain. 



Each section is provided with a stout plate-glass window placed 

 in the center of the section on the operating side of the gallery 

 through which the progress of any flame produced in the gallery 

 may be viewed and noted, while an indicator cock, tapped into the 

 central section, provides a means by which samples of the mixtures 

 in the gallery may be taken for analysis. 



The gallery is so connected with the natural-gas supply used in 

 Pittsburg that it may be filled with gas at will, and the quantity 



