Caput mortuum
Caput mortuum is a Latin term whose literal meaning is "dead head" or "worthless remains", used in alchemy.
Caput mortuum signified a useless substance left over from a chemical operation such as sublimation and the epitome of decline and decay; alchemists represented this residue with a stylized human skull, a literal death's head.
The symbol shown on this page was also used in 18th-century chemistry to mean residue, remainder or residuum. Caput mortuum was also sometimes used to mean crocus metallorum, i.e. brownish-red metallic compounds such as crocus martis, and crocus veneris.
