F. Isherwood, Chief Engineer, U. S. N., it appears that the Collin's steamers use anthracite on the voyage to Liverpool, and Welsh coal, also an anthracite, on the return voyage. The Welsh coal ...

These originally formed the bitumen of the coal, which does not exist in anthracite; this latter being ... quantity of bituminous coal, a& from the raw coal itself. Thus, for example if we suppose ...