athanor

from WordNet (r) 3.0 (2006)

athanor
    n 1: a furnace that feeds itself so as to maintain a uniform
         temperature; used by alchemists

from The Collaborative International Dictionary of English v.0.48

Athanor \Ath"a*nor\, n. [F., fr. Ar. at-tann[=u]r, fr. Heb.
   tann[=u]r an oven or furnace.]
   A digesting furnace, formerly used by alchemists. It was so
   constructed as to maintain uniform and durable heat.
   --Chambers.
   [1913 Webster]