Potassium alum
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IUPAC name
Potassium alum[2]
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Other names
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Identifiers | |
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3D model (
JSmol ) |
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ChEBI | |
ECHA InfoCard
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100.112.464 |
E number | E522 (acidity regulators, ...) |
PubChem CID
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UNII |
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Properties | |
KAl(SO4)2·12H2O | |
Molar mass | 258.192 g/mol (anhydrous) 474.37 g/mol (dodecahydrate) |
Appearance | White crystals |
Odor | Watery metallic |
Density | 1.725 g/cm3 |
Melting point | 92 to 95 °C (198 to 203 °F; 365 to 368 K) |
Boiling point | Decomposes at 200[3] °C (392 °F; 473 K) |
14.00 g/100 mL (20,5°C) 36.80 g/100 mL (50 °C) | |
Solubility in other solvents | Insoluble in acetone |
Refractive index (nD)
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1.4564 |
Hazards | |
NFPA 704 (fire diamond) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound: the double sulfate of potassium and aluminium, with chemical formula KAl(SO4)2. It is commonly encountered as the dodecahydrate, KAl(SO4)2·12H2O. It crystallizes in an octahedral structure in neutral solution and cubic structure in an alkali solution with space group P a −3 and lattice parameter of 12.18 Å.[4] The compound is the most important member of the generic class of compounds called alums, and is often called simply alum.[5]
Potassium alum is commonly used in water purification, leather tanning, dyeing,[6] fireproof textiles, and baking powder as E number E522. It also has cosmetic uses as a deodorant, as an aftershave treatment and as a styptic for minor bleeding from shaving.[7][8]
History
Historically, potassium alum was used extensively in the wool industry
Antiquity
Egypt
Potassium alum was also known to the Ancient Egyptians, who obtained it from evaporites in the Western desert and reportedly used it as early as 1500 BCE to reduce the visible cloudiness (turbidity) in the water.[citation needed]
Mesopotamia
According to the expert on Middle Eastern history of chemistry Martin Levey, potassium alum is one of the few compounds known to the ancients that can be found relatively pure in nature, as well as one of only a few chemicals used in Mesopotamian chemical technology that can be identified with certainty.[10] Both native and imported potassium alum was used.[10] Together with other agents, potassium alum was used in glass-making, tanning, and in the dyeing of cloth, wood, and possibly hair.[10] A tanning process using potassium alum is described in tablets from the first millennium BCE.[10] When Levey wrote his article in 1958, no description of the dyeing process had been found, so it is not known how potassium alum was used in it. In Mesopotamian medicine potassium alum was used extensively, for example against itch, jaundice, some eye condition, and unidentified ailments.[10]
According to Levey, potassium alum was used in "classical times" as a flux when soldering copper, in the fireproofing of wood, and in the separation of silver and gold, but that there is no evidence that these uses existed in Mesopotamia.[10]
Greece
The production of potassium alum from alunite is archaeologically attested on the island Lesbos.[11] This site was abandoned in the 7th century but dates back at least to the 2nd century CE.
Rome
Potassium alum was described under the name alumen or salsugoterrae by
India and China
Potassium alum is mentioned in some[
Middle Ages
In the 13th and 14th centuries, alum (from alunite) was a major import from
Modern era
England
Potassium alum was imported into England mainly from the
With state financing, attempts were made throughout the 16th century, but without success until the early 17th century. An industry was founded in
Identification of the formula
In the early 1700s, Georg Ernst Stahl claimed that reacting sulfuric acid with limestone produced a sort of alum.
Marggraf also showed that perfect crystals with properties of alum can be obtained by dissolving alumina in sulfuric acid and adding potash or ammonia to the concentrated solution.[23][24] In 1767, Torbern Bergman observed the need for potassium or ammonium sulfates to convert aluminium sulfate into alum, while sodium or calcium would not work.[23][25]
At the time, potassium ("potash") was believed to be exclusively found on plants. However, in 1797, Martin Klaproth discovered the presence of potassium in the minerals leucite and lepidolite.[26][27]
Louis Vauquelin then conjectured that potassium was likewise an ingredient in many other minerals. Given Marggraf and Bergman's experiments, he suspected that this alkali constituted an essential ingredient of natural alum. In 1797 he published a dissertation demonstrating that alum is a double salt, composed of sulfuric acid, alumina, and potash.[28] In the same journal volume, Jean-Antoine Chaptal published the analysis of four different kinds of alum, namely, Roman alum, Levant alum, British alum and alum manufactured by himself,[29] confirming Vauquelin's results.[23]
Characteristics
Potassium alum crystallizes in regular
3.[citation needed
When heated to nearly a red heat, it gives a porous, friable mass, which is known as "burnt alum". It fuses at 92 °C (198 °F) in its own water of crystallization.[citation needed]
Natural occurrence
Potassium alum dodecahydrate occurs in nature as a
In the past, potassium alum has been obtained from
In order to obtain alum from
The undecahydrate also occurs as the fibrous mineral kalinite (KAl(SO
4)
2·11H
2O).[32]
Industrial production
Potassium alum historically was mainly extracted from alunite.
Potassium alum is now produced industrially by adding potassium sulfate to a concentrated solution of aluminium sulfate.[33] The aluminium sulfate is usually obtained by treating minerals like alum schist, bauxite and cryolite with sulfuric acid.[34] If much iron should be present in the sulfate then it is preferable to use potassium chloride in place of potassium sulfate.[34]
Uses
Medicine and cosmetics
Potassium alum is used in medicine mainly as an
Potassium alum is also used topically to remove
It is used in dentistry (especially in gingival retraction cords) because of its
Potassium and
Potassium alum was the major immunologic adjuvant used to increase the efficacy of vaccines, and has been used since the 1920s.[43] But it has been almost completely replaced by aluminium hydroxide and aluminium phosphate in commercial vaccines.[44]
Alum may be used in depilatory waxes used for the removal of body hair or applied to freshly waxed skin as a soothing agent.
In the 1950s, men sporting crewcut or flattop hairstyles sometimes applied alum to their hair, as an alternative to pomade, to keep the hair standing up.[citation needed]
Culinary
Potassium alum may be an acidic ingredient of
Alum was used by bakers in England during the 1800s to make bread whiter. This was theorized by some, including
Potassium alum, under the name "alum powder", is found in the spice section of many grocery stores in the US. Its chief culinary use is in pickling recipes, to preserve and add crispness to fruit and vegetables.[49]
Flame retardant
Potassium alum is used as a fire retardant to render cloth, wood, and paper materials less flammable.[33]
Tanning
Potassium alum is used in leather tanning,[50] in order to remove moisture from the hide and prevent rotting.[citation needed] Unlike tannic acid, alum doesn't bind to the hide and can be washed out of it.[citation needed]
Dyeing
Alum has been used since antiquity as mordant to form a permanent bond between dye and natural textile fibers like wool.[51] It is also used for this purpose in paper marbling.[52]
Chemical flocculant
Potassium alum has been used since remote antiquity for purification of turbid liquids.[53] It is still widely used in the purification of water for drinking and industrial processes water, treatment of effluents and post-storm treatment of lakes to precipitate contaminants.[54]
Between 30 and 40
The same principle is exploited when using alum to increase the viscosity of a ceramic glaze suspension; this makes the glaze more readily adherent and slows its rate of sedimentation.[citation needed]
Lake pigments
Aluminum hydroxide from potassium alum serves as a base for the majority of lake pigments.[57]
Dissolving iron and steel
Alum solution has the property of dissolving steels while not affecting aluminium or
Other
In traditional Japanese art, alum and animal glue were dissolved in water, forming a liquid known as dousa (ja:礬水), and used as an undercoat for paper sizing.[citation needed]
Alum is an ingredient in some recipes for homemade modeling compounds, often called "play clay" or "play dough", intended for use by children.[citation needed]
Potassium alum was formerly used as a hardener for photographic emulsions (films and papers), usually as part of the fixer. It has now been replaced in that use by other chemicals.
Toxicology and safety
Potassium alum may be a weak irritant to the skin.[60]
See also
- Ammonium aluminium sulfate
- Alum
References
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Works cited
- public domain: Chisholm, Hugh, ed. (1911). "Alum". Encyclopædia Britannica. Vol. 1 (11th ed.). Cambridge University Press. pp. 766–767. This article incorporates text from a publication now in the