Ambergris (ambergrease or grey amber) is a waxy, inflammable solid with a dull grey colour formed as a biliary secretion in the gut of sperm whales. It is thought to act as a protective lubricant so that squid beaks and other hard, sharp ojects the whale may swallow don’t pierce its intestine.
Its main use was as a fixative in perfumes. Alluded to in the Rush song Panacea from their 1975 album Caress of Steel in the line:
I catch the scent of ambergris and turn my head, surprised
Fresh ambergris actually has an oceanic, fecal odour when first expelled by the whale, but happily acquires a sweet, earthy scent commonly not dissimilar to the smell of rubbing alcohol but without the “chemical” astringency, which presumably was what turned Geddy’s head, not the smell of whale poo.
According to its Wikipedia entry, ambergris is relatively non-reactive to acid. White crystals of ambrein can be separated from ambergris by heating raw ambergris in alcohol, then allowing the resulting solution to cool. Ambrein is fairly odourless but breaks down to ambrox and ambrinol, which give it its characteristic sweet scent.
Today, ambergris has been replaced by synthetic agents, such as ambroxan. However, 83 kg of ambergris in the intestine of a recently stranded whale is estimated to be worth €500,000.