extended tests have been made as to the explosibility of various
mixtures of gas and air; as to the explosibility of dust from various
typical coals; as to the chemical composition and physical
characteristics of this dust; the degree of fineness necessary to the
most explosive conditions; and the methods of dampening the dust by
water, by humidifying, by steam, or of deadening its explosibility by
the addition of calcium chloride, stone dust, etc. A bulletin outlining
the results thus far obtained in the study of the coal-dust problem is
now in course of publication.[3]

After reviewing the history of observations and experiments with coal
dust carried on in Europe, and later, the experiments at the French,
German, Belgian, and English explosives-testing stations, this bulletin
takes up the coal-dust question in the United States. Further chapters
concern the tests as to the explosibility of coal dust, made by the
Geological Survey, at Pittsburg; investigations, both at the Pittsburg
laboratory and in mines, as to the humidity of mine air. There is also a
chapter on the chemical investigations into the ignition of coal dust by
Dr. J. C. W. Frazer, of the Geological Survey. The application of some
of these data to actual mine conditions in Europe, in the last year, is
treated by Mr. Axel Larsen; the use of exhaust steam in a mine of the
Consolidation Coal Company, in West Virginia, is discussed by Mr. Frank
Haas, Consulting Engineer; and the use of sprays in Oklahoma coal mines
is the subject of a chapter by Mr. Carl Scholz, Vice-President of the
Rock Island Coal Mining Company.

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,