What is "alembroth"

Alembroth \A*lem"broth\ (-br[o^]th), n. [Origin uncertain.] The salt of wisdom of the alchemists, a double salt composed of the chlorides of ammonium and mercury. It was formerly used as a stimulant.
--Brande & C.

n. (context archaic English) The "salt of wisdom" of the alchemists, a double salt composed of the chlorides of ammonium and mercury, formerly used as a stimulant.