am-ber-gris n. A waxy, grayish substance formed in the intestines of sperm whales and found floating at sea or washed ashore. It is added to perfumes to slow down the rate of evaporation. [American Heritage Dictionary 3rd Edition]
The lexicographer who wrote this definition did not read Chapters 91 and 92.
Fun was poked at German whalers in Chapter 81 when the Pequod met the Jungfrau. Here fun is poked at French whalers. The premise is that the "Bouton de Rose" [Rose Bud], a French whaleship, is encoutered by the Pequod in the act of cutting in a "blasted" -- long dead and putrefying -- whale, one that smelled to high heaven. Stubb sees that the French ship has also picked up a potential gold mine of a whale. Lashed to the other side of the Rose Bud is a Sperm Whale that obviously died a slow death, drying up of a sickness that is associated with the production of a mass within it known as ambergris -- worth more than its weight in gold to the perfume industry.
Wily Stubb concocts a plan to hoodwink the "Crappoes" [French crapaud: toad] out of their ambergris-bearing whale. He convinces the gullible, inexperienced French captain that a blasted whale causes death by fever, and that the dried-up whale is more dangerous than that. The frightened captain thanks Stubb for hauling the dried-up whale away, and then he takes off, leaving the blasted whale in his wake as well.
Stubb and his boat crew greedily dig into the smelly, shrivelled carcass and are rewarded with handfuls of ambergris -- just as impatient Ahab commands them back to the Pequod.
This is one of the very few chapters in which we find absolutely no profound pronouncements on the vicissitudes and vagaries of life and the human condition. It is informative, introducing the reader to an interesting, arcane subject -- but one not especially critical to the development of Melville's story.