Read it through once

Assuming the blubber to be the skin of the whale; then, when this skin, as in the case of a very large Sperm Whale, will yield the bulk of one hundred barrels of oil; and, when it is considered that, in quantity, or rather weight, that oil, in its expressed state, is only three fourths, and not the entire substance of the coat; some idea may hence be had of the enormousness of that animated mass, a mere part of whose mere integument yields such a lake of liquid as that. Reckoning ten barrels to the ton, you have ten tons for the net weight of only three quarters of the stuff of the whale’s skin.