A method using the gas-comparison pycnometer with helium gas as the penetrating medium measures precisely the true volume of a pulverized coal sample. The true density of a solid is calculated as the true unit volume of the solid exclusive of its pore space which is divided into the weight of the sample.
The method is similar to that used to determine the density of refractory materials but the procedure is modified to yield precise density determinations of coal samples. These modifications diminish effects of trapped moisture and gases on the volume measurement.
The helium gas-comparison pycnometer method is rapid, reliable, precise, and requires minimal analytical equipment and sample preparation, and also is non-destructive to the coal sample. Using this method, densities can be determined on coal samples of subbituminous to low-volatile bituminous rank and perhaps also on samples of lignite. The density of anthracite samples has not been determined by this method.
Additional publication details
USGS Numbered Series
Determination of the true density of pulverized coal samples