![Caput mortuum](https://upload.wikimedia.org/wikipedia/commons/7/7e/Caput_mortuum.svg)
''Caput mortuum'' (plural ''capita mortua'') is a
Latin term
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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)''
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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