View source for Potassium alum

{{Use dmy dates|cs1-dates=ll|date=August 2024}}
{{chembox
| Verifiedfields = changed
| Watchedfields  = changed
| verifiedrevid  = 450596278
| Name           = Potassium alum
| ImageFile      = Potassium alum.jpg
| ImageFile1     = Potassium-alum-3D-vdW.png
| ImageSize      = 250px
| IUPACName      = Potassium alum<ref>{{RedBook2005}}</ref>
| OtherNames     = {{Unbulleted list|Potassium alum sulfate|Potash alum|Alum-(K)<ref name="WebMineral" />}}
| SystematicName =
| Section1       = {{Chembox Identifiers
| CASNo = 10043-67-1
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo2_Ref = {{cascite|correct|CAS}}
| CASNo2 = 7784-24-9
| CASNo2_Comment = (dodecahydrate)<!-- Aldrich-validated -->
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 09OXB01F3O
| UNII2_Ref = {{fdacite|correct|FDA}}
| UNII2 = 1L24V9R23S
| UNII2_Comment = (dodecahydrate)
| PubChem = 24856
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 86463
| SMILES = [O-]S(=O)(=O)[O-].[O-]S(=O)(=O)[O-].[Al+3].[K+]
| InChI = 1S/Al.K.2H2O4S/c;;2*1-5(2,3)4/h;;2*(H2,1,2,3,4)/q+3;+1;;/p-4
}}
| Section2       = {{Chembox Properties
| Formula = KAl(SO<sub>4</sub>)<sub>2</sub>·12H<sub>2</sub>O
| MolarMass = 258.192 g/mol (anhydrous)<br />474.37 g/mol (dodecahydrate)
| Appearance = White crystals
| Odor = Watery metallic
| Density = 1.725 g/cm<sup>3</sup>
| Solubility = 14.00 g/100 mL (20,5°C) <br /> 36.80 g/100 mL (50 °C)
| SolubleOther = Insoluble in acetone
| Solvent = other solvents
| MeltingPtC = 92 to 95
| MeltingPt_notes =
| BoilingPt = Decomposes at
| BoilingPtC = 200<ref>{{Cite web |url= https://fscimage.fishersci.com/msds/19200.htm |title=Material Safety Data Sheet - Aluminum potassium sulfate dodecahydrate |access-date=26 July 2020 |archive-date=25 October 2020 |archive-url= https://web.archive.org/web/20201025130732/https://fscimage.fishersci.com/msds/19200.htm |url-status=live}}</ref>
| RefractIndex = 1.4564
}}
| Section3       = {{Chembox Hazards
| NFPA-H = 2
| NFPA-F = 0
| NFPA-R = 0
}}
| Section4       =
| Section5       =
| Section6       =
}}
'''Potassium alum''', '''potash alum''', or '''potassium aluminium sulfate''' is a [[chemical compound]] first mentioned under various [[Sanskrit]] names in Ayurvedic medicinal texts such as {{lang|sa-Latn|charak samhita}}, {{lang|sa-Latn|sushrut samhita}}, and {{lang|sa-Latn|ashtang hridaya}}; is chemically defined as the double [[sulfate]] of [[potassium]] and [[aluminium]], with chemical formula KAl(SO<sub>4</sub>)<sub>2</sub>.  It is commonly encountered as the [[hydrate|dodecahydrate]], KAl(SO<sub>4</sub>)<sub>2</sub>·12H<sub>2</sub>O. It crystallizes in an octahedral structure in neutral solution and cubic structure in an alkali solution with space group Pa{{overline|3}} and lattice parameter of 12.18 Å.<ref>{{cite web |url= http://crystallography.net/cod/1011177.html |website=Crystallography Open Database |title=Crystal structure of the alums |date=1934 |access-date=15 April 2018 |archive-date=15 April 2018 |archive-url= https://web.archive.org/web/20180415125042/http://crystallography.net/cod/1011177.html |url-status=live}}</ref> The compound is the most important member of the generic class of compounds called [[alum]]s, and is often called simply '''alum'''.<ref>{{Cite book |last1=Bottomley |first1=L. |last2=Bottomley |first2=L. A. |title=Chemistry 1310: Laboratory Manual |publisher=School of Chemistry & Biochemistry, Georgia Institute of Technology / Hayden-McNeil Publishing |location=Plymouth, Michigan |date=2010 |isbn=978-0-7380-3819-3}}</ref>

Potassium alum is commonly used in [[water purification]], [[leather]] tanning, [[dyeing]],<ref>{{cite encyclopedia |url= http://www.britannica.com/EBchecked/topic/17885/alum |title=alum &#124; chemical compound |encyclopedia=Britannica.com |access-date=18 January 2016 |archive-date=26 May 2015 |archive-url= https://web.archive.org/web/20150526003249/http://www.britannica.com/EBchecked/topic/17885/alum |url-status=live}}</ref> fireproof [[textile]]s, and [[baking powder]] as [[E number]] '''E522'''. It also has cosmetic uses as a deodorant, as an aftershave treatment and as a [[Antihemorrhagic|styptic]] for minor bleeding from shaving.<ref name="AlumAbout.com">{{cite web |url= http://chemistry.about.com/od/moleculescompounds/f/What-Is-Alum.htm |title=What is Alum? |publisher=About.com |access-date=19 April 2013 |last=Helmenstine |first=Anne Marie |archive-date=14 April 2013 |archive-url= https://web.archive.org/web/20130414205755/http://chemistry.about.com/od/moleculescompounds/f/What-Is-Alum.htm |url-status=live}}</ref><ref name="Blake n Blade">{{cite web |url= https://blakenblade.com/alum-block-for-shaving-how-to-guide |title=Alum Block for Shaving – When and How to Use One |archive-url= https://web.archive.org/web/20200115180407/https://blakenblade.com/alum-block-for-shaving-how-to-guide |archive-date=15 January 2020 |work=BlakenBlade.com |publisher=Blake'n Blade Shave Shop |access-date=15 January 2020}}</ref>

==History==
Historically, potassium alum was used extensively in the wool industry<ref>See [[Henry VII of England]] trade section. Henry broke the Pope's monopoly by financing shipping bootstrapping a trading system with the Ottoman Empires mines</ref> from [[Classical antiquity]], during the [[Middle Ages]], and well into 19th century as a [[dye fixative|mordant or dye fixative]] in the process of turning wool into [[dye]]d [[bolt (fabric)|bolts of cloth]].{{citation needed|date = September 2016}}

=== Antiquity ===

==== Egypt ====
Potassium alum was also known to the [[Ancient Egypt]]ians, who obtained it from [[evaporite]]s in the Western desert and reportedly used it as early as 1500 BCE to reduce the visible cloudiness ([[turbidity]]) in the water.{{citation needed|date=December 2020}}

==== 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 [[Mesopotamia|Mesopotamian]] chemical technology that can be identified with certainty.<ref name=":0">{{Cite journal |last=Levey |first=Martin |date=1958 |title=Alum in Ancient Mesopotamian Technology |url= https://www.jstor.org/stable/226929 |journal=Isis |volume=49 |issue=2 |pages=166–169 |doi=10.1086/348667 |jstor=226929 |via=JSTOR}}</ref> Both native and imported potassium alum was used.<ref name=":0" /> Together with other agents, potassium alum was used in [[History of glass|glass-making]], [[Tanning (leather)|tanning]], and in the [[Dyeing|dyeing of cloth]], wood, and possibly hair.<ref name=":0" /> A tanning process using potassium alum is described in tablets from the first millennium BCE.<ref name=":0" /> 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 [[Mesopotamia#Medicine|Mesopotamian medicine]] potassium alum was used extensively, for example against itch, [[jaundice]], some eye condition, and unidentified ailments.<ref name=":0" /> 

According to Levey, potassium alum was used in "classical times" as a [[Flux (metallurgy)|flux]] when [[Soldering#Pipe soldering|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.<ref name=":0" />

==== Greece ====
The production of potassium alum from [[alunite]] is archaeologically attested on the island [[Lesbos]].<ref>A. Archontidou 2005, "Un atelier de preparation de l'alun a partir de l'alunite dans l'isle de Lesbos" in ''L'alun de Mediterranée''. ed P. Borgard et al.</ref> 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 [[Pliny the Elder|Pliny]],<ref name="pliny">[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.02.0137%3Abook%3D35%3Achapter%3D52 Alumen, and the Several Varieties of it; Thirty-eight Remedies.] {{Webarchive|url= https://web.archive.org/web/20210422170440/http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.02.0137%3Abook%3D35%3Achapter%3D52|date=22 April 2021}}, [[Pliny the Elder]], ''The Natural History'', book 35, chapter 52; on the Perseus Digital Library at [[Tufts University]]. Last accessed 27 December 2011.</ref> and it is clearly the same as the ''stypteria'' (στυπτηρία) described by [[Dioscorides]].<ref name="dios">Dioscorides, book 5, chapter 123.</ref>  However, the name ''alum'' and other names applied to this substance — like ''misy'', ''sory'', ''chalcanthum'', and ''atramentum sutorium'' — were often applied to other products with vaguely similar properties or uses, such as [[iron(II) sulfate|iron sulfate]] or "green vitriol".{{sfn|Chisholm|1911|pp=766–767}}{{full citation needed|date=November 2021}}

==== India and China ====
Potassium alum is mentioned in  Ayurvedic texts namely Charak Samhita, Sushurta Samhita, and Ashtanga Hridaya with the name such as ''sphaṭika kṣāra'',  ''phitkari'' or ''saurashtri''. It is used in [[traditional Chinese medicine]] with the name ''mingfan'' .

===Middle Ages===
In the 13th and 14th centuries, alum (from alunite) was a major import from [[Phocaea]] ([[Gulf of Smyrna]] in Byzantium) by Genoans and Venetians (and was a cause of war between [[Genoa]] and [[Venice]]) and later by [[Florence]]. After the fall of [[Constantinople]], alunite (the source of alum) was discovered at [[Tolfa]] in the Papal States (1461). The textile dyeing industry in [[Bruges]], and many locations in Italy, and later in England, required alum to stabilize the dyes onto the fabric (make the dyes "fast") and also to brighten the colors.<ref>"Color in Relation to the Political and Economic History of the Western World" by Sidney M Edelstein, Proceedings of the Perkin Centennial, American Association of Textile Chemists and Colorists, September 1956</ref><ref>"Worldly Goods: A New History of the Renaissance", Lisa Jardine, 1996, Norton&Co, pages 114–116 {{ISBN|978-0393318661}}</ref>

=== Modern era ===

==== England ====
Potassium alum was imported into England mainly from the [[Middle East]], and, from the late 15th century onwards, the [[Papal States]] for hundreds of years. Its use there was as a [[dye]]-fixer ([[mordant]]) for [[wool]] (which was one of England's primary industries, the value of which increased significantly if dyed).{{cn|date=September 2023}} These sources were unreliable, however, and there was a push to develop a source in England especially as imports from the Papal States ceased following the [[excommunication]] of [[Henry VIII of England|Henry VIII]].<ref>{{cite web |title=How alum shaped the Yorkshire coast |url= https://www.nationaltrust.org.uk/yorkshire-coast/features/how-alum-shaped-the-yorkshire-coast |url-status=live |archive-url= https://web.archive.org/web/20171203180500/https://www.nationaltrust.org.uk/yorkshire-coast/features/how-alum-shaped-the-yorkshire-coast |archive-date=3 December 2017 |access-date=5 February 2018 |publisher=National Trust, UK}}</ref>

With state financing, attempts were made throughout the 16th century, but without success until the early 17th century. An industry was founded in [[Yorkshire]] to process the [[shale]], which contained the key ingredient, [[aluminium sulfate]], and made an important contribution to the [[Industrial Revolution]]. One of the oldest historic sites for the production of alum from shale and [[human urine]] are the Peak alum works in [[Ravenscar, North Yorkshire|Ravenscar]], North Yorkshire. By the 18th century, the landscape of northeast Yorkshire had been devastated by this process, which involved constructing {{convert|100|ft|adj=on}} stacks of burning shale and fuelling them with firewood continuously for months. The rest of the production process consisted of quarrying, extraction, steeping of shale ash with seaweed in urine, boiling, evaporating, crystallisation, milling and loading into sacks for export. Quarrying ate into the cliffs of the area, the forests were felled for charcoal and the land polluted by sulfuric acid and ash.<ref>{{cite news |first=Stephen |last=Chance |url= https://www.theguardian.com/uk-news/the-northerner/2013/nov/20/alum-makers-secret-north-east-manufacturing |title=Was alum the first example of the north-east's 'dirty' industries? &#124; UK news |newspaper=The Guardian |date=20 November 2013 |access-date=25 March 2017 |archive-date=17 May 2017 |archive-url= https://web.archive.org/web/20170517075429/https://www.theguardian.com/uk-news/the-northerner/2013/nov/20/alum-makers-secret-north-east-manufacturing |url-status=live}}</ref>

==== Identification of the formula ====
In the early 1700s, Georg Ernst Stahl claimed that reacting sulfuric acid with limestone produced a sort of alum.<ref name="stahl1">George Ernst Stahl (1703), [http://www.e-rara.ch/zut/content/pageview/4572022 ''Specimen Beccherianum''] {{Webarchive|url= https://web.archive.org/web/20180205130124/http://www.e-rara.ch/zut/content/pageview/4572022 |date=5 February 2018 }}. Johann Ludwig Gleditsch, [[Leipzig]].</ref><ref name="stahl2">George Ernst Stahl (1723), [https://books.google.com/books?id=nvVlAAAAcAAJ&pg=PA305 ''Ausführliche Betrachtung und zulänglicher Beweiss von den Saltzen, daß diesselbe aus einer zarten Erde, mit Wasser innig verbunden, bestehen''] {{Webarchive|url= https://web.archive.org/web/20161222083433/https://books.google.com/books?id=nvVlAAAAcAAJ&pg=PA305 |date=22 December 2016 }} (Detailed treatment and adequate proof of salts, that they consist of a subtile earth intimately bound with water) Wäysenhaus, [[Halle (region)|Halle]].</ref>  The error was soon corrected by [[Johann Heinrich Pott|Johann Pott]] and [[Andreas Sigismund Marggraf|Andreas Marggraf]], who showed that the [[precipitation (chemistry)|precipitate]] obtained when an alkali is poured into a [[Solution (chemistry)|solution]] of alum, namely [[alumina]], is quite different from [[lime (mineral)|lime]] and [[chalk]], and is one of the ingredients in common [[clay]].<ref>Johann Heinrich Pott (1746), [https://books.google.com/books?id=uxZAAAAAcAAJ&pg=PA32 ''Chymische Untersuchungen, welche fürnehmlich von der Lithogeognosia oder Erkäntniß und Bearbeitung der gemeinen einfacheren Steine und Erden ingleichen von Feuer und Licht handeln''] {{Webarchive|url= https://web.archive.org/web/20161222073831/https://books.google.com/books?id=uxZAAAAAcAAJ&pg=PA32 |date=22 December 2016 }}, volume 1, p. 32.</ref><ref>Andreas Sigismund Marggraf (1754), [http://babel.hathitrust.org/cgi/pt?id=nyp.33433009864186;view=1up;seq=51 "Expériences faites sur la terre d'alun"] {{Webarchive|url= https://web.archive.org/web/20181106195425/https://babel.hathitrust.org/cgi/pt?id=nyp.33433009864186;view=1up;seq=51 |date=6 November 2018 }} (Experiments made on the earth of alum), ''Mémoires de l'Académie des sciences et belles-lettres de Berlin'', pp. 41–66.</ref>

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.{{sfn|Chisholm|1911|p=766}}<ref>Marggraf (1754) [http://babel.hathitrust.org/cgi/pt?id=nyp.33433009864186;view=1up;seq=41 "Expériences qui concernent la régénération de l'alun de sa propre terre, l'après avoir séparé par l'acide vitriolique ; avec quelques compositions artificielles de l'alun par moyen d'autres terres, et dudit acide"] {{Webarchive|url= https://web.archive.org/web/20181106201749/https://babel.hathitrust.org/cgi/pt?id=nyp.33433009864186;view=1up;seq=41 |date=6 November 2018 }}. ''Mémoires de l'Académie des sciences et belles-lettres de Berlin'', pp. 31–40.</ref>  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.{{sfn|Chisholm|1911|p=766}}<ref>Torbern Bergman (1767),  [https://books.google.com/books?id=HcuNbkfxYQMC&pg=PA307 ''"IX. De confectione Aluminis"''] {{Webarchive|url= https://web.archive.org/web/20210423013549/https://books.google.com/books?id=HcuNbkfxYQMC&pg=PA307 |date=23 April 2021 }}. In ''Opuscula physica et chemica'', I. G. Müller, Leipzig, 1788), volume 1, pp. 306–307.</ref>

At the time, potassium ("potash") was believed to be exclusively found on plants. However, in 1797, [[Martin Heinrich Klaproth|Martin Klaproth]] discovered the presence of potassium in the minerals [[leucite]] and [[lepidolite]].<ref>Martin Heinrich Klaproth (1797), [https://babel.hathitrust.org/cgi/pt?id=nyp.33433066422746;view=1up;seq=65 ''Beiträge zur Chemischen Kenntniss Der Mineralkörper''] {{Webarchive|url= https://web.archive.org/web/20181106200122/https://babel.hathitrust.org/cgi/pt?id=nyp.33433066422746;view=1up;seq=65 |date=6 November 2018 }} (Contributions to [our] chemical knowledge of mineral substances).  Decker and Co., Posen, and Heinrich August Rottmann, Berlin; pp. 45–46 and https://babel.hathitrust.org/cgi/pt?id=nyp.33433066422746;view=1up;seq=213 {{Webarchive|url= https://web.archive.org/web/20181106201757/https://babel.hathitrust.org/cgi/pt?id=nyp.33433066422746;view=1up;seq=213 |date=6 November 2018 }} p. 193.</ref><ref>Martin Heinrich Klaproth (1801), ''Analytical Essays Towards Promoting the Chemical Knowledge of Mineral Substances''. T. Cadell, Jr. & W. Davies, London.  His finding of potassium in leucite appears on [https://archive.org/stream/analyticalessay01klapgoog#page/n374/mode/2up pp. 353–354.]: "On the contrary, I was surprised in an unexpected manner, by discovering in it another constituent part, consisting of a substance, the existence of which, certainly, no one person would have conjectured within the limits of the mineral kingdom&nbsp;.... This constituent part of leucite&nbsp;... is no other than ''pot-ash'', which, hitherto, has been thought {{em|exclusively}} to belong to the {{em|vegetable kingdom}}, and has, on this account, been called {{em|vegetable alkali}}.&nbsp;... This discovery, which I think of great importance, cannot fail to occasion considerable changes in the systems of natural history&nbsp;...".  The discovery of potassium in lepidolite is mentioned on [https://archive.org/stream/analyticalessay01klapgoog#page/n494/mode/2up p. 472.]</ref>

[[Louis Nicolas Vauquelin|Louis Vauquelin]] then conjectured that potassium was likewise an ingredient in many other [[mineral]]s.  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.<ref>Vauquelin (1797), [http://babel.hathitrust.org/cgi/pt?id=mdp.39015065209101;view=1up;seq=266 "Sur la nature de l'Alun du commerce, sur l'existence de la potasse dans ce sel, et sur diverses combinaisons simples ou triples de l'alumine avec l'acide sulfurique"] {{Webarchive|url= https://web.archive.org/web/20181106194826/https://babel.hathitrust.org/cgi/pt?id=mdp.39015065209101;view=1up;seq=266 |date=6 November 2018 }} (On the nature of commercial alum, on the existence of potash in this salt, and on various simple or triple compounds of alumina with sulfuric acid). In ''Annales de Chimie et de Physique'', 1st series, volume 22, pages 258–279.</ref> 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,<ref>Jean-Antoine Chaptal (1797), [http://babel.hathitrust.org/cgi/pt?id=mdp.39015065209101;view=1up;seq=288 "Comparée des quatre principales sortes d'Alun connues dans le commerce; et Observations sur leur nature et leur usage"] {{Webarchive|url= https://web.archive.org/web/20181106201816/https://babel.hathitrust.org/cgi/pt?id=mdp.39015065209101;view=1up;seq=288 |date=6 November 2018 }} (Comparison of the four main types of commercial alum; and observations on their nature and use). In ''Annales de Chimie et de Physique'', 1st series, volume 22, pages 280–296.</ref> confirming Vauquelin's results.{{sfn|Chisholm|1911|p=766}}

==Characteristics==
[[File:Potassium alum octahedral like crystal.jpg|thumb|[[Octahedral]] potassium alum crystal with unequal distribution of the face area]]
Potassium alum crystallizes in regular [[octahedra]] with flattened corners and is very soluble in water. The solution is slightly acidic and is [[astringent]] to the taste.  Neutralizing a solution of alum with [[potassium hydroxide]] will begin to cause the separation of alumina {{chem|Al(|OH|)|3}}.{{cn|date=September 2023}}

When heated to nearly a red heat, it gives a porous, friable mass, which is known as "burnt alum". It fuses at {{convert|92|°C|°F}} in its own [[water of crystallization]].{{cn|date=September 2023}}

==Natural occurrence==
Potassium alum dodecahydrate occurs in nature as a [[sulfate mineral]] called [[alum-(K)]], typically as encrustations on rocks in areas of [[weathering]] and [[oxidation]] of [[sulfide mineral]]s and potassium-bearing minerals.{{cn|date=September 2023}}

In the past, potassium alum has been obtained from [[alunite]] ({{chem|KAl(SO|4|)|2|·2Al(OH)|3}}), mined from sulfur-containing volcanic sediments.<ref>Bottomley (2010) p. 35.</ref> Alunite is an associate and likely potassium and aluminium source.<ref name="WebMineral">{{cite web |url= http://webmineral.com/data/Alum-%28K%29.shtml |title=Alum-(K) Mineral Data |publisher=Mineralogy Database |access-date=19 April 2013 |archive-date=24 April 2013 |archive-url= https://web.archive.org/web/20130424121644/http://webmineral.com/data/Alum-(K).shtml |url-status=live}}</ref><ref name="MinDat">{{cite web |url= http://www.mindat.org/show.php?id=3267 |title=Alum-(K) mineral data and information |publisher=MinDat |access-date=19 April 2013 |archive-date=3 July 2013 |archive-url= https://web.archive.org/web/20130703082652/http://www.mindat.org/show.php?id=3267 |url-status=live}}</ref> It has been reported at [[Vesuvius]], [[Italy]]; east of [[Springsure]], [[Queensland]]; in Alum Cave, [[Tennessee]]; Alum Gulch, [[Santa Cruz County, Arizona]] and the [[Philippines|Philippine]] island of [[Cebu]].

In order to obtain alum from [[alunite]], it is [[calcined]] and then exposed to the action of air for a considerable time. During this exposure it is kept continually moistened with water, so that it ultimately falls to a very fine powder. This powder is then lixiviated with hot water, the liquor decanted, and the alum allowed to crystallize.{{cn|date=September 2023}}

The [[Hydrate|undecahydrate]] also occurs as the fibrous mineral [[kalinite]] ({{chem|KAl(SO|4|)|2|·11H|2|O}}).<ref>{{cite web |url= http://webmineral.com/data/Kalinite.shtml |title=Kalinite Mineral Data |publisher=MinDat |access-date=19 April 2013 |archive-date=24 April 2013 |archive-url= https://web.archive.org/web/20130424135717/http://webmineral.com/data/Kalinite.shtml |url-status=live}}</ref>

==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]].<ref name="Ullmann">Otto Helmboldt, L. Keith Hudson, Chanakya Misra, Karl Wefers, Wolfgang Heck, Hans Stark, Max Danner, Norbert Rösch "Aluminium Compounds, Inorganic" in Ullmann's Encyclopedia of Industrial Chemistry 2007, Wiley-VCH, Weinheim.{{doi|10.1002/14356007.a01_527.pub2}}</ref>  The aluminium sulfate is usually obtained by treating minerals like alum [[schist]], [[bauxite]] and [[cryolite]] with sulfuric acid.{{sfn|Chisholm|1911|p=767}}  If much iron should be present in the sulfate then it is preferable to use [[potassium chloride]] in place of potassium sulfate.{{sfn|Chisholm|1911|p=767}}

==Uses==

===Medicine and cosmetics===
[[File:Potassium Alum Block India Shaving Aftershave.jpg|thumb|An ammonium alum block sold as an [[astringent]] in pharmacies in India (where it is widely known as ''Fitkiri (Bengali), Fitkari (Hindi)” <ref name="handa16">{{cite book |last1=Handa |first1=Parvesh |title=Herbal beauty care |date=1982 |publisher=Orient Paperbacks |location=New Delhi |isbn=9788122200249 |page=12 |url= https://books.google.com/books?id=QlXQBtaMU7AC&pg=PA12 |access-date=7 January 2016}}</ref>]]

Potassium alum is used in medicine mainly as an [[astringent]] (or [[styptic]]) and [[antiseptic]].

[[Styptic pencil]]s are rods composed of potassium alum or aluminum sulfate, used topically to reduce bleeding in minor cuts (especially from [[shaving]]) and abrasions, [[epistaxis|nosebleeds]], and [[hemorrhoids]], and to relieve pain from stings and bites.{{citation needed|date=June 2015}}  Potassium alum blocks are rubbed over the wet skin after shaving.<ref name="Blake n Blade" />

Potassium alum is also used topically to remove [[pimple]]s and [[acne]], and to cauterize [[aphthous ulcers]] in the mouth and [[canker sore]]s, as it has a significant drying effect to the area and reduces the irritation felt at the site.<ref name="canker">{{Cite web |title=Canker Sores – Treatment & Prevention |url= https://lagunaparkdentistry.com/blog/canker-sores-treatment-and-prevention |archive-url= https://web.archive.org/web/20230609172514/https://lagunaparkdentistry.com/blog/canker-sores-treatment-and-prevention |archive-date=9 June 2023 |access-date=16 August 2023 |website=lagunaparkdentistry.com}}</ref><ref name="philstar">{{Cite news |last=Ong |first=Willie T. |title=Singaw: Ano ang lunas? |work=[[Philippine Star]] |url= https://www.philstar.com/pilipino-star-ngayon/opinyon/2018/10/18/1860929/singaw-ano-ang-lunas |access-date=16 August 2023 |archive-url= https://web.archive.org/web/20211101051633/https://www.philstar.com/pilipino-star-ngayon/opinyon/2018/10/18/1860929/singaw-ano-ang-lunas |archive-date=1 November 2021}}</ref> It has been used to stop bleeding in cases of [[hemorrhagic cystitis]]<ref>{{Cite journal |title=Use of Alum to Control Intractable Vesical Haemorrhage |first1=C. |last1=Kennedy |first2=M. E. |last2=Snell |first3=R. E. |last3=Witherow |journal=British Journal of Urology |volume=56 |issue=6 |pages=673–675 |date=1984 |doi=10.1111/j.1464-410X.1984.tb06143.x |pmid=6534488}}</ref> and is used in some countries as a cure for [[hyperhidrosis]].{{citation needed|date=February 2018}}

It is used in dentistry (especially in gingival retraction cords) because of its [[astringent]] and [[hemostatic]] properties.{{citation needed|date=June 2015}}

Potassium and [[ammonium alum]] are the active ingredients in some [[antiperspirant]]s and [[deodorant]]s, acting by inhibiting the growth of the [[bacteria]] responsible for [[body odor]].  Alum's antiperspirant and antibacterial properties<ref>{{cite journal |last1=Kanlayavattanakul |first1=M. |last2=Lourith |first2=N. |title=Body malodours and their topical treatment agents |journal=International Journal of Cosmetic Science |date=1 August 2011 |volume=33 |issue=4 |pages=298–311 |doi=10.1111/j.1468-2494.2011.00649.x |pmid=21401651 |s2cid=11235250 |doi-access=free}}</ref><ref>{{cite journal |last1=Aguilar |first1=T. N. |last2=Blaug |first2=S. M. |last3=Zopf |first3=L. C. |title=A study of the antibacterial activity of some complex aluminum salts |journal=Journal of the American Pharmaceutical Association |date=July 1956 |volume=45 |issue=7 |pages=498–500 |pmid=13345689 |doi=10.1002/jps.3030450720}}</ref> contribute to its traditional use as an underarm [[deodorant]].<ref name="pliny" /> It has been used for this purpose in Europe, Mexico, Thailand (where it is called ''sarn-som''), throughout Asia and in the Philippines (where it is called ''tawas''). Today, potassium or ammonium alum is sold commercially for this purpose as a "deodorant crystal".<ref>{{cite patent |country=US |number=5399364 |status=patent |title=Cosmetic assembly defined by encased stick of alum |gdate=1995-05-21 |fdate=1993-06-09 |inventor=Francis Verdan |url= https://www.google.com/patents/US5399364}} [https://patents.google.com/patent/US5399364]</ref><ref>{{Cite book |url= https://books.google.com/books?id=tM_0BgAAQBAJ |title=Introduction to Cosmetic Formulation and Technology |last1=Baki |first1=Gabriella |last2=Alexander |first2=Kenneth S. |date=27 April 2015 |publisher=John Wiley & Sons |isbn=9781118763780 |pages=324 |access-date=5 February 2018 |archive-date=16 February 2017 |archive-url= https://web.archive.org/web/20170216015843/https://books.google.com/books?id=tM_0BgAAQBAJ |url-status=live}}</ref><ref name="AlumAbout.com" />  Beginning in 2005 the US [[Food and Drug Administration]] no longer recognized it as a wetness reducer, but it is still available and used in several other countries, primarily in Asia.{{citation needed|date=February 2018}}

Potassium alum was the major [[immunologic adjuvant]] used to increase the efficacy of [[vaccine]]s, and has been used since the 1920s.<ref>{{Cite journal |title=Alum's adjuvant action: Grease is the word |first1=M. Lamine |last1=Mbow |first2=Ennio |last2=De Gregorio |first3=Jeffrey B. |last3=Ulmer |journal=Nature Medicine |volume=17 |issue=4 |pages=415–416 |date=2011 |doi=10.1038/nm0411-415 |pmid=21475229 |s2cid=6343632}}</ref> But it has been almost completely replaced by [[aluminium hydroxide]] and [[aluminium phosphate]] in commercial vaccines.<ref>{{cite journal |title=Towards an understanding of the adjuvant action of aluminium |journal=Nature Reviews Immunology |first1=Philippa |last1=Marrack |first2=Amy S. |last2=McKee |first3=Michael W. |last3=Munks |date=2009 |issn=1474-1733 |volume=9 |issue=4 |pages=287–293 |doi=10.1038/nri2510 |pmid=19247370 |pmc=3147301}}</ref>

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|date=November 2008}}

===Culinary===
Potassium alum may be an acidic ingredient of [[baking powder]] to provide a second [[leavening]] phase at high temperatures (although [[sodium aluminum sulfate|sodium alum]] is more commonly used for that purpose).{{citation needed|reason=Reference needed to verify this claim.|date=February 2018}} For example, potassium alum is frequently used in leavening of {{lang|zh-Latn|[[youtiao]]}}, a traditional Chinese fried bread, throughout China.<ref>{{cite journal |last1=Li |first1=G. |last2=Zhao |first2=X. |last3=Wu |first3=S. |last4=Hua |first4=H. |last5=Wang |first5=Q. |last6=Zhang |first6=Z. |title=Dietary exposure to aluminium in the popular Chinese fried bread youtiao |journal=Food Additives & Contaminants – Part A: Chemistry, Analysis, Control, Exposure & Risk Assessment |date=June 2017 |volume=34 |issue=6 |pages=972–979 |doi=10.1080/19440049.2017.1306757 |pmid=28332421 |s2cid=24675971}}</ref>

Alum was used by bakers in England during the 1800s to make bread whiter. This was theorized by some, including [[John Snow]], to cause [[rickets]].<ref>{{cite web |url= http://www.ph.ucla.edu/epi/snow/injepidemiology32_336_337_2003.pdf |title=On the adulteration of bread as a cause of rickets |website=ucla.edu |access-date=5 February 2018 |archive-date=19 April 2021 |archive-url= https://web.archive.org/web/20210419001036/http://www.ph.ucla.edu/epi/snow/injepidemiology32_336_337_2003.pdf |url-status=live}}</ref><ref>{{cite magazine |title=Brown Bread |magazine=The Church of England Magazine |volume=22 |date=January–June 1847 |page=355 |url= https://books.google.com/books?id=xRURAAAAIAAJ |publisher=Church Pastoral-aid Society, London}}</ref> The [[Sale of Food and Drugs Act 1875]] ([[38 & 39 Vict.]] c. 63) prevented this and other adulterations.<ref>{{Cite book |last=Hassall |first=Arthur Hill |title=Adulterations detected; or, Plain instructions for the discovery of frauds in food and medicine |date=1857 |publisher=Longman, Brown, Green, Longmans & Roberts |url= https://archive.org/details/adulterationsde00hassgoog |page=[https://archive.org/details/adulterationsde00hassgoog/page/n61 43]}}</ref>

Potassium alum, under the name "alum powder", is found in the spice section of many grocery stores in the [[United States|US]]. Its chief culinary use is in [[pickling]] recipes, to preserve and add crispness to fruit and vegetables.<ref>{{Cite book |url= https://books.google.com/books?id=1QZrL3YPHeUC&q=Alum+powder,+found+in+the+spice+section+of+many+grocery+stores,+may+be+used+in+pickling+recipes&pg=PA15 |title=The Flower Recipe Book |last1=Harampolis |first1=Alethea |last2=Rizzo |first2=Jill |date=2013 |publisher=Artisan Books |isbn=9781579655303}}</ref>

===Flame retardant===
Potassium alum is used as a [[fire retardant]] to render cloth, wood, and paper materials less flammable.<ref name="Ullmann" />

===Tanning===
Potassium alum is used in [[leather]] [[tanning (leather)|tanning]],<ref>{{Cite book |url= https://books.google.com/books?id=G7tUPQdT2hcC&q=Alum+is+used+in+the+tanning+of+animal+hides&pg=PA24 |title=Bookbinding & Conservation by Hand: A Working Guide |last=Young |first=Laura S. |date=1995 |publisher=Oak Knoll Press |isbn=9781884718113 |access-date=2 November 2020 |archive-date=8 October 2021 |archive-url= https://web.archive.org/web/20211008193141/https://books.google.com/books?id=G7tUPQdT2hcC&q=Alum+is+used+in+the+tanning+of+animal+hides&pg=PA24 |url-status=live}}</ref> in order to remove moisture from the [[Hide (skin)|hide]] and prevent rotting.{{citation needed|date=October 2014}}  Unlike [[tannic acid]], alum doesn't bind to the hide and can be washed out of it.{{citation needed|date=January 2017}}

===Dyeing===
Alum has been used since antiquity as [[mordant]] to form a permanent bond between [[dye]] and natural textile fibers like [[wool]].<ref>{{Cite book |url= https://archive.org/details/mechanicandchem00berggoog |page=[https://archive.org/details/mechanicandchem00berggoog/page/n33 91] |title=The Mechanic and Chemist |last=Berger |first=G. |date=1840}}</ref> It is also used for this purpose in [[paper marbling]].<ref>{{cite book |last=Berry |first=Galen |title=The Art of Marbling on Paper and Fabric |date=2017 |page=6}}</ref>

===Chemical flocculant===
Potassium alum has been used since remote antiquity for purification of turbid liquids.<ref name="faust">{{cite book |title=Chemistry of water treatment |date=1999 |publisher=Ann Arbor Press |location=Chelsea, Michigan |isbn=9781575040110 |url= https://books.google.com/books?id=ivLiNH-NjOcC&q=alum+flocculation&pg=PA217 |first1=Samuel D. |last1=Faust |first2=Osman M. |last2=Aly |edition=2nd |access-date=2 November 2020 |archive-date=8 October 2021 |archive-url= https://web.archive.org/web/20211008193149/https://books.google.com/books?id=ivLiNH-NjOcC&q=alum+flocculation&pg=PA217 |url-status=live}}</ref> It is still widely used in the purification of water for drinking and industrial processes water, treatment of [[effluent]]s and post-storm treatment of lakes to precipitate contaminants.<ref>{{cite web |url= http://www.engr.wisc.edu/news/archive/2013/aug20.html |title=Storm water treatment will strip phosphorus from Arboretum pond, College of Engineering @ the University of Wisconsin-Madison, initiatives in energy, health, nanotechnology, security, and information technology |publisher=Engr.wisc.edu |access-date=18 January 2016 |archive-url= https://web.archive.org/web/20150921113606/https://www.engr.wisc.edu/news/archive/2013/aug20.html |archive-date=21 September 2015}}</ref>

Between 30 and 40 [[Parts per million|ppm]] of alum<ref name="faust" /><ref>{{cite book |last=Bratby |first=John |title=Coagulation and flocculation in water and wastewater treatment |date=2006 |publisher=IWA Publ. |location=London |isbn=9781843391067 |url= https://books.google.com/books?id=vmkNROg_ehMC&q=alum+flocculation |edition=2nd}}</ref> for household wastewater, often more for industrial wastewater,<ref>{{cite journal |last=Rice |first=J. K. |title=The use of organic flocculants and flocculating aids in the treatment of industrial water and industrial waste water |journal=Symposium on Industrial Water and Industrial Waste Water |date=June 1957 |issue=207 |pages=41–51 |doi=10.1520/STP39285S |isbn=978-0-8031-5629-6 |url= https://books.google.com/books?id=yNwM-GWgraUC&q=alum+flocculation&pg=PA49 |access-date=2 November 2020 |archive-date=8 October 2021 |archive-url= https://web.archive.org/web/20211008193142/https://books.google.com/books?id=yNwM-GWgraUC&q=alum+flocculation&pg=PA49 |url-status=live}}</ref> is added to the water so that the negatively charged colloidal particles clump together into "[[flocculation|flocs]]", which then float to the top of the liquid, [[Settling|settle]] to the bottom of the liquid, or can be more easily [[Filtration|filtered]] from the liquid, prior to further filtration and disinfection of the water.<ref name="Ullmann" /> Like other similar salts, it works by neutralizing the [[electrical double layer]] surrounding very fine suspended particles, allowing them to join into flocs.

The same principle is exploited when using alum to increase the [[viscosity]] of a [[ceramic glaze]] [[suspension (chemistry)|suspension]]; this makes the glaze more readily adherent and slows its rate of [[sedimentation]].{{cn|date=September 2023}}

===Lake pigments===
Aluminum hydroxide from potassium alum serves as a base for the majority of [[lake pigment]]s.<ref>{{Cite book |url= https://books.google.com/books?id=00Duxp3RIjkC&q=%22Alum%22+serves+as+a+base+for+the+majority+of+lake+pigments.&pg=PA55 |title=Painted Prints: The Revelation of Color in Northern Renaissance & Baroque Engravings, Etchings, & Woodcuts |last=Dackerman |first=Susan |date=2002 |publisher=Penn State Press |isbn=978-0271022352 |access-date=2 November 2020 |archive-date=8 October 2021 |archive-url= https://web.archive.org/web/20211008193123/https://books.google.com/books?id=00Duxp3RIjkC&q=%22Alum%22+serves+as+a+base+for+the+majority+of+lake+pigments.&pg=PA55 |url-status=live}}</ref>

===Dissolving iron and steel===
Alum solution has the property of dissolving steels while not affecting aluminium or [[base metals]]. Alum solution can be used to dissolve steel tool bits that have become lodged in machined castings.<ref>https://www.youtube.com/watch?v=fqZYgReuywM {{Webarchive|url= https://web.archive.org/web/20171119225633/https://www.youtube.com/watch?v=fqZYgReuywM&feature=youtu.be |date=19 November 2017 }} AvE demonstrates use of alum to remove a broken stud from an aluminium engine head</ref><ref>{{cite web |url= http://www.model-engineer.co.uk/forums/postings.asp?th=91442&p=82#PostTop |title=What did you do today? (2014) |publisher=Model Engineer |access-date=25 March 2017 |archive-date=2 August 2017 |archive-url= https://web.archive.org/web/20170802044515/http://www.model-engineer.co.uk/forums/postings.asp?th=91442&p=82#PostTop |url-status=live}}</ref>

===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]].{{cn|date=September 2023}}

Alum is an ingredient in some recipes for homemade modeling compounds, often called "play clay" or "play dough", intended for use by children.{{cn|date=September 2023}}

Potassium alum was formerly used as a hardener for [[photographic emulsion]]s (films and papers), usually as part of the [[photographic fixer|fixer]]. It has now been replaced in that use by other chemicals.

==Toxicology and safety==
Potassium alum may be a weak [[Irritation|irritant]] to the skin.<ref>{{cite journal |last1=Gallego |first1=H. |last2=Lewis |first2=E. J. |last3=Crutchfield |first3=C. E. III |title=Crystal deodorant dermatitis: Irritant dermatitis to alum-containing deodorant |journal=Cutis |volume=64 |issue=1 |pages=65–6 |date=July 1999 |pmid=10431678}}</ref>
<!--Does not need to be expanded; not very toxic.-->

==See also==
* [[Ammonium aluminium sulfate]]
* [[Alum]]

==References==
{{reflist}}

===Works cited===
* {{EB1911 |wstitle=Alum |volume=1 |pages=766-767}}

{{potassium compounds}}
{{aluminium compounds}}
{{sulfur compounds}}

[[Category:Sulfate minerals]]
[[Category:Potassium compounds]]
[[Category:Aluminium compounds]]
[[Category:Water treatment]]
[[Category:Coordination complexes]]
[[Category:Potash]]
[[Category:E-number additives]]