or Alcahest, in chemistry, an universal menstruum capable of resolving all bodies in- to their first principles. Van Helmont pretended he was possessed of such a menstruum; but, however cre- dulous people might be imposed on in his days, the no- tion is now become as ridiculous as the philosopher's stone, the perpetuum mobile, &c.—It is likewise used by some authors for all fixed salts volatilized.