“May 15, 1909.

“LIST OF PERMISSIBLE EXPLOSIVES.
“Tested prior to May 15, 1909.

“As a part of the investigation of mine explosions authorized by
Congress in May, 1908, it was decided by the Secretary of the Interior
that a careful examination should be made of the various explosives
used in mining operations, with a view to determining the extent to
which the use of such explosives might be responsible for the
occurrence of these disasters.

“The preliminary investigation showed the necessity of subjecting to
rigid tests all explosives intended for use in mines where either gas
or dry inflammable dust is present in quantity or under conditions
which are indicative of danger.

“With this in view, a letter was sent by the Director of the United
States Geological Survey on January 9, 1909, to the manufacturers of
explosives in the United States, setting forth the conditions under
which these explosives would be examined and the nature of the tests
to which they would be subjected.

“Inasmuch as the conditions and tests described in this letter were
subsequently followed in testing the explosives given in the list
below, they are here reproduced, as follows:

“(1) The manufacturer is to furnish 100 pounds of each explosive which
he desires to have tested; he is to be responsible for the care,
handling, and delivery of this material at the testing station on the