''Caput mortuum'' (plural ''capita mortua'') is a

Latin term __NOTOC__ This is a list of Wikipedia articles of Latin phrases and their translation into English. ''To view all phrases on a single, lengthy document, see: List of Latin phrases (full)'' The list also is divided alphabetically into twenty page ...

whose literal meaning is "dead head" or "worthless remains", used in

alchemy Alchemy (from Arabic: ''al-kīmiyā''; from Ancient Greek: χυμεία, ''khumeía'') is an ancient branch of natural philosophy, a philosophical and protoscientific tradition that was historically practiced in China, India, the Muslim world, ...

. ''Caput mortuum'' (alternately called ''

nigredo In alchemy, nigredo, or blackness, means putrefaction or decomposition. Many alchemists believed that as a first step in the pathway to the philosopher's stone, all alchemical ingredients had to be cleansed and cooked extensively to a uniform blac ...

'') 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'' (

ferrous sulfate Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula Fe SO4·''x''H2O. These compounds exist most commonly as the hepta hydrate (''x'' = 7) but several values for x are kno ...

), and ''crocus veneris'' ( copper oxidule).

References

{{reflist Alchemical substances Latin words and phrases