An earlier bulletin setting forth the literature and certain mine investigations of explosive gases and dust,[4] has already been issued. After treating of methods of collecting and analyzing the gases found in mines, of investigations as to the rate of liberation of gas from coal, and of studies on coal dust, this bulletin discusses such factors as the restraining influence of shale dust and dampness on coal-dust explosions. It then takes up practical considerations as to the danger of explosions, including the relative inflammability of old and fresh coal dust. The problems involved are undergoing further investigation and elaboration, in the light of information already gathered.
Permissible Explosives.—The most important progress in these tests and investigations has been made in those relating to the various explosives used in getting coal from mines. Immediately upon the enactment of the first legislation, in the spring of 1908, arrangements
were perfected whereby the lower portion of the old Arsenal grounds belonging to the War Department and adjacent to the Pennsylvania Railroad, on the Alleghany River, at 40th and Butler Streets, Pittsburg, Pa., were transferred to the Interior Department for use in these investigations. Meantime, in anticipation of the appropriation, Mr. Clarence Hall, an engineer experienced in the manufacture and use of explosives, was sent to Europe to study the methods of testing explosives practiced at the Government stations in Great Britain, Germany, Belgium, and France. Mr. Joseph A. Holmes also visited Europe for the purpose of studying methods of ameliorating conditions in the mines. Three foreign mining experts, the chiefs of investigating bureaus in Belgium, Germany, and England, spent three months studying conditions in the United States at the invitation of the Secretary of the Interior, to whom they submitted a valuable report.[5]
Under the supervision of the writer, Chief Engineer of these investigations, detailed plans and specifications had been prepared in advance for the necessary apparatus and the transformation of the buildings at Pittsburg to the purposes of this work. It was possible, therefore, to undertake immediately the changes in existing buildings, the erection of new buildings, the installation of railway tracks, laboratories, and the plumbing, heating, and lighting plant, etc. This work was carried on with unusual expedition, under the direction of the Assistant Chief Engineer, Mr. James C. Roberts, and was completed within a few months, by which time most of the apparatus was delivered and installed.
One building (No. 17) is devoted to the smaller physical tests of explosives. It was rendered fire resistant by heavily covering the floors, ceiling, and walls with cement on metal lath, and otherwise protecting the openings. In it are installed apparatus for determining calorific value of explosives, pressure produced on ignition, susceptibility to ignition when dropped, rate of detonation, length and duration of flame, and kindred factors. Elsewhere on the grounds is a gallery of boiler-steel plate, 100 ft. long and more than 6 ft. in diameter, solidly attached to a mass of concrete at one end, in which is embedded a cannon from which to discharge the explosive under test, and open at the other end, and otherwise so constructed as to
simulate a small section of a mine gallery (Fig. 2, [Plate VI]). The heavy mortar pendulum, for the pendulum test for determining the force produced by an explosive, is near by, as is also an armored pit in which large quantities of explosive may be detonated, with a view to studying the effects of magazine explosions, and for testing as to the rate at which ignition of an explosive travels from one end to the other of a cartridge, and the sensitiveness of one cartridge to explosion by discharge of another near by.
In another building (No. 21), is a well-equipped chemical laboratory for chemical analyses and investigations of explosives, structural materials, and fuels.
Several months were required to calibrate the various apparatus, and to make analyses of the available natural gas to determine the correct method of proportioning it with air, so as to produce exact mixtures of 2, 4, 6, or 8% of methane with air. Tests of existing explosives were made in air and in inflammable mixtures of air and gas, with a view to fixing on some standard explosive as a basis of comparison. Ultimately, 40% nitro-glycerine dynamite was adopted as the standard. Investigative tests having been made, and the various factors concerning all the explosives on the market having been determined, a circular was sent to all manufacturers of explosives in the United States, on January 9th, 1909, and was also published in the various technical journals, through the associated press, and otherwise.
On May 15th, 1909, all the explosives which had been offered for test, as permissible, having been tested, the first list of permissible explosives was issued, as given in the following circular:
“EXPLOSIVES CIRCULAR NO. 1.