Ishmael briefly describes the “case” or “tun” in which the sperm whale’s spermaceti, or oil, is stored. This case is in the upper part of the head, and nearly runs for a third of the whale’s body. A large whale can yield 500 gallons of spermaceti, and much if not all of this is caught and bucketed by the sailors on the ship—if they are careful, and do not spill the oil into the sea or on the decks.
Sperm oil is, of course, the ultimate goal of any whaling voyage. Ishmael describes the two ways this oil can be harvested from a dead whale. The first is from melting down the whale’s blubber, which has been collected by skinning the whale. And the second is by collecting the whale’s excess oil, located in a large “hold” in the whale’s skull.