REGULUS, in Chemistry, the metallic matter that falls to the bottom of the crucible, in the melting of ores or impure metallic substances. It is the finest or purest part of the metal; and, according to the alchemists, is denominated regulus, or little king, as being the first-born of the royal metallic blood. According to them, it is really a son, but not a perfect man; i. e. not yet a
perfect metal, for want of time and proper nourishment. To procure the regulus of metals, &c. flux powders are commonly used; as nitre, tartar, &c. which purge the sulphureous part adhering to the metal, by attracting and absorbing it to themselves.