Anthracite, burning sizes

The rate of combustion is the weight of coal burned per square foot of grate per hour. It may be expressed by Rc == m /d, where d = draft between ashpit and furnace, in inches of water, and m = 17 to 32 for anthracite (increasing with the size), 80 and 60 for bituminous run-of-rniiie and slack, and 50 for run-of-mine semi-bituminous coal. 

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