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Litharge
Litharge is one of the natural mineral forms of lead(II) oxide, PbO. Litharge is a secondary mineral which forms from the oxidation of galena ores. It forms as coatings and encrustations with internal tetragonal crystal structure. It is dimorphous with the orthorhombic form massicot. It forms soft (Mohs hardness of 2), red, greasy-appearing crusts with a very high specific gravity of 9.14–9.35. PbO may be prepared by heating lead metal in air at approx. 600°C (lead melts at only 300°C). At this temperature it is also the end product of oxidation of other lead oxides in air. 〔N.N. Greenwood, A. Earnshaw, "Chemistry of Elements", 2nd edition, Butterworth-Heinemann, 1997.〕 This is often done with a set of bellows pumping air over molten lead and causing the oxidized product to slip/ fall off the top into a receptacle where it quickly solidifies in minute scales.〔http://chestofbooks.com/health/materia-medica-drugs/Treatise-Therapeutics-Pharmacology-Materia-Medica-Vol1/VI-Semivitrified-Oxide-Of-Lead-Oxide-Of-Lead-Plumbi-Ox.html#.UYdA2crhfU4〕
:PbO2 –(293 °C)→ Pb12O19 –(351 °C)→ Pb12O17 –(375 °C)→ Pb3O4 –(605 °C)→ PbO
==Historical terminology==
Historically, the term "litharge" has been combined to refer to other similar substances. For example, ''litharge of gold'' is litharge mixed with red lead, giving it a red color; ''litharge of silver'' is litharge that comes as a by-product of separating silver from lead; ''litharge of bismuth'' is a similar result of the oxidation of bismuth. The term has also been used as a synonym for white lead or red lead.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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