Fig. 1.--Explosion from Coal Dust in Gas and Dust Gallery No. 1.

Fig. 2.--Mine Gallery No. 1.

Fig. 3.--Ballistic Pendulum.]

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.
“DEPARTMENT OF THE INTERIOR.
“United States Geological Survey.