PERMISSIBLE EXPLOSIVES TESTED PRIOR TO JANUARY 1, 1911, AND PRECAUTIONS TO BE TAKEN IN THEIR USE.

GENERAL STATEMENT.

This circular contains the names of permissible explosives that have been tested by the Bureau of Mines at Pittsburg, Pa., and precautions to be observed when these explosives are used in coal mines. Permissible explosives give a short and relatively cool flame that is less likely to ignite inflammable gas or coal dust than is the longer and hotter flame of dynamite or the longer and much more lasting flame of black powder, and are intended for use in those coal mines where the presence of such gas or dust may render a mine explosion possible. Because they can be used with greater safety, permissible explosives have taken the place of other explosives in many coal mines in the United States during the last two years, and their use is increasing rapidly.

Whether or not an explosive has the good qualities of those explosives classed as "permissible" is something that can be found out only suitable equipment in a mining experiment station at Pittsburg, Pa. by careful tests. To carry on such tests the Government has placed The station is under the charge of the Bureau of Mines, which is directed by law to search for means by which the work of the miner

can be made safer.

This circular states the conditions under which explosives are accepted for testing, the tests the explosives now have to pass, the names of the explosives that have passed the tests, and some of the dangers that should be avoided in storing and using explosives. The United States Geological Survey, which formerly had charge of the station at Pittsburg, Pa., has published in three circulars the names of those explosives, and all permissible explosives tested subsequent to of the explosives that passed similar tests prior to May 16, 1910. All May 16, 1910, and prior to January 1, 1911, except such as have been withdrawn by the makers or have not satisfied later tests, are named

in this circular.

74844-11

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