Rock Dusting - This machine, called a trickle duster, emits a cloud of finely-powdered limestone into the passageway which carries air currents away from from the working face of a coal mine in the United States. The limestone mixes with fine coal dust carried way by ventilating currents; a proper portion of the incombustible limestone averts the danger of an explosion from the combustible coal dust.
Photo measures 10.25 x 8 inches.
Photo is dated --0000.
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