Excerpt from Analyses of Coals Purchased by the Government During the Fiscal Years 1908-1915
The analyses given herein are of samples taken from commercial deliveries. In making a comparison of analyses of commercial ship ments with analyses of samples collected from the face of the bed in the mine, due allowance must be made for the larger proportion of impurities that may be included in the commercial operation of the mine. It is difficult to take a mine sample in which the impurities are rejected in exactly the same manner as is done by the miner. The practice of different miners will vary, especially if rigid inspec tion at the tipple is not enforced. In some mines, for instance, where the coal bed has friable partings or has a soft, ﬂaky roof or ﬂoor, the inclusion of some foreign matter is unavoidable. Hence, the analysis of the mine sample usually indicates a better grade of coal, as regards ash content and heating value, than the actual commercial shipments, and for this reason the mine sample should be considered as representing the coal that can be produced under only the most favorable conditions of mining and preparation.
In commercial shipments that are sampled at their destination the moisture content may be either more or less than that in the mine samples, the relative proportions depending on the amount of bed moisture, the size of the coal, and the weather conditions during transit.
Analyses representing many shipments and a large tonnage more truly indicate the general quality of a particular coal than does a single analysis from a. Specially prepared shipment, or analyses of carefully selected mine samples.
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