Editing Alum

{{Short description|Family of double sulfate salts of aluminium}}
{{About|the class of double sulfates of aluminium|the specific representative compound|potassium alum|the chromium analogs|chrome alum|papermakers' alum|aluminium sulfate|a graduate or former student of an educational institution|alumni|other uses}}

[[File:Kaaliumi maarjase monikristallid2.JPG|thumb|upright=1.5|Crystal of potassium alum, {{chem|KAl|(|SO|4|)|2|·12H|2|O}}]]

An '''alum''' ({{IPAc-en|ˈ|æ|l|ə|m}}) is a type of [[chemical compound]], usually a [[hydrate]]d [[double salt|double]] [[sulfate]] [[salt (chemistry)|salt]] of [[aluminium]] with the general [[chemical formula|formula]] {{chem|{{mvar|X}}Al|(|SO|4|)|2|·12 H|2|O}}, such that {{mvar|X}} is a [[valence (chemistry)|monovalent]] [[cation]] such as [[potassium]] or [[ammonium]].<ref name=Austin-1984-Shreves/> By itself, "alum" often refers to [[potassium alum]], with the formula {{chem|KAl|(|SO|4|)|2|·12 H|2|O}}. Other alums are named after the monovalent ion, such as [[sodium alum]] and [[ammonium alum]].

The name "alum" is also used, more generally, for salts with the same formula and structure, except that aluminium is replaced by another [[Valence (chemistry)|trivalent]] metal ion like [[chromium#Chromium(III)|chromium{{sup|III}}]], or sulfur is replaced by another [[chalcogen]] like [[selenium]].<ref name="Austin-1984-Shreves" /> The most common of these analogs is [[chrome alum]] {{chem|K|Cr|(|SO|4|)|2|·12 H|2|O}}.

In most industries, the name "alum" (or "papermaker's alum") is used to refer to [[aluminium sulfate]], {{chem|Al|2| (SO|4|)|3|·{{mvar|n}} {{chem|H|2|O}}}}, which is used for most industrial [[flocculation]]<ref name="Austin-1984-Shreves" />{{rp|page=766}} (the variable {{mvar|n}} is an integer whose size depends on the amount of water absorbed into the alum). For [[medicine]], the word "alum" may also refer to [[aluminium hydroxide]] gel used as a [[immunologic adjuvant|vaccine adjuvant]].<ref name="InvivoGen-Alum-adjvt" />

==History==

===Alum found at archaeological sites===
The western desert of Egypt was a major source of alum substitutes in antiquity. These [[evaporite]]s were mainly {{chem|Fe|Al|2|(SO|4|)|4|·22 H|2|O}}, {{chem|Mg|Al|2|(SO|4|)|4|·22 H|2|O}}, {{chem|NaAl(SO|4|)|2|·6 H|2|O}}, {{chem|Mg|SO|4|·7H|2|O}} and {{chem|Al|2|(SO|4|)|3|·17 H|2|O}}.{{refn|name=Picon-etal-2005-lAlun|
{{cite conference
 |author1=Picon, M.
 |author-link=Maurice Picon
 |display-authors=etal
 |date=2005
 |title=L'alun des oasis occidentales d'Egypte: Researches sur terrain et recherches en laboratoire}} 
}} <ref name="Borgard-Brun-Picon-2005-06-07-alunMedit" />
The [[Ancient Greece|Ancient Greek]] [[Herodotus]] mentions Egyptian alum as a valuable commodity in ''The Histories''.<ref name=Herodotus-c430ʙᴄᴇ-Hists/>

The production of potassium alum from [[alunite]] is archaeologically attested on the island [[Lesbos]].{{refn|name=Archontidou-2005-alunMedit|
{{cite conference
 |last=Archontidou |first=A.
 |date=2005
 |title=Un atelier de preparation de l'alun a partir de l'alunite dans l'isle de Lesbos
 |language=fr,grc
}}
<ref name="Borgard-Brun-Picon-2005-06-07-alunMedit" />
}}
The site was abandoned during the 7th&nbsp;century&nbsp;CE, but dates back at least to the 2nd&nbsp;century&nbsp;CE. Native ''alumen'' from the island of [[Melos]] appears to have been a mixture mainly of alunogen ({{chem|Al|2|(SO|4|)|3|·17 H|2|O}}) with potassium alum and other minor sulfates.{{refn|name=Hall-Jones-2005-alunMedit|
{{cite conference
 |first1=A. J. |last1=Hall 
 |first2=E. |last2=Photos-Jones
 |date=2005
 |title=The nature of Melian alumen and its potential for exploitation in Antiquity
}}
<ref name="Borgard-Brun-Picon-2005-06-07-alunMedit" />
}}

===Alumen in Pliny and Dioscorides===
A detailed description of a substance termed ''alumen'' occurs in the [[Roman Empire|Roman]] [[Pliny the Elder]]'s ''[[Natural History (Pliny)|Natural History]]''.<ref name="PlinySr-NatHist" />

By comparing Pliny's description with the account of ''stypteria'' (στυπτηρία) given by [[Dioscorides]],<ref name="Dioscor-MatMed" /> it is obvious the two are identical. Pliny informs us that a form of ''alumen'' was found naturally in the earth, and terms it ''salsugoterrae''.

Pliny wrote that different substances were distinguished by the name of ''alumen'', but they were all characterised by a certain degree of [[Astringent|astringency]], and were all employed for dyeing and medicine. Pliny wrote that there is another kind of alum that the ancient [[Ancient Greece|Greeks]] term ''schiston'', and which "splits into filaments of a whitish colour".<ref name=PlinySr-NatHist/> From the name ''schiston'' and the mode of formation, it seems that this kind was the salt that forms spontaneously on certain salty minerals, as alum [[slate]] and bituminous [[shale]], and consists mainly of sulfates of iron and aluminium.{{citation needed|date=May 2009}} One kind of ''alumen'' was a liquid, which was apt to be adulterated; but when pure it had the property of blackening when added to [[pomegranate]] juice. This property seems to characterize a [[Solution (chemistry)|solution]] of [[Iron(II) sulfate|iron{{sup|II}} sulfate]] in water; a solution of ordinary (potassium) alum would possess no such property. Contamination with iron sulfate was greatly disliked as this darkened and dulled dye colours. In some places the iron sulfate may have been lacking, so the salt would be white and would be suitable, according to Pliny, for dyeing bright colors.

Pliny describes several other types of alumen but it is not clear as to what these minerals are. The ''alumen'' of the ancients, then, was not always potassium alum, not even an alkali aluminum sulfate.<ref name=Chisholm-1911/>{{rp|pages=&nbsp;766–767}}

===Alum described in medieval texts===
Alum and [[Iron(II) sulfate|green vitriol]] (iron sulfate) both have sweetish and astringent taste, and they had overlapping uses. Therefore, through the [[Middle Ages]], alchemists and other writers do not seem to have distinguished the two salts accurately. In the writings of the [[Alchemy|alchemists]] we find the words ''misy'', ''sory'', and ''chalcanthum'' applied to either compound; and the name ''atramentum sutorium'', which one might expect to belong exclusively to green vitriol, applied indiscriminately to both.{{citation needed|date=June 2023}}

Alum was the most common [[mordant]] (substance used to set dyes on fabrics) used by the dye industry, especially in Islamic countries, during the [[Islamic Golden Age|middle ages]]. It was the main export of the [[Chad]] region, from where it was transported to the markets of [[Egypt]] and [[Morocco]], and then to [[Europe]].  Less significant sources were found in Egypt and [[Yemen]].<ref name=Goitein-Sanders-1967/>

===Modern understanding of the alums===
During the early 1700s, [[Georg Ernst Stahl|G. E. Stahl]] claimed that reacting sulfuric acid with limestone produced a sort of alum.<ref name=Stahl-1703/>{{efn|
CVII.  ''Vitriolum, ''Creta'' præcipitari potest, ut omissa metallica sua substantia, ''aluminosum'' evadat.''
:
:[107.  Sulfuric acid {{grey|[and]}} ''chalk'' can {{grey|[form a]}} precipitate, as its liberated metallic substance, ''alum'', escapes.]
:
''Ausführliche Betrachtung und zulänglicher Beweiss von den Saltzen, daß diesselbe aus einer zarten Erde, mit Wasser innig verbunden, bestehen''
:
:[Detailed treatment and adequate proof of salts, that they consist of a subtile earth intimately bound with water]
:::— G. E. Stahl (1703)<ref name=Stahl-1703/>}}{{efn|Wäysenhaus, [[Halle (region)|Halle]]
''...&nbsp;wie aus Kreide und Vitriole-Spiritu, ein rechter Alaun erwächset:&nbsp;...''
:
:[...&nbsp;as from chalk and sulfuric acid, a real alum arises&nbsp;...]
:::— G. E. Stahl (1723)<ref name=Stahl-1723/>}}<ref name=Stahl-1723/> The error was soon corrected by [[Johann Heinrich Pott]] and [[Andreas Sigismund Marggraf]], who showed that the [[Precipitation (chemistry)|precipitate]] obtained when an alkali is poured into a solution of alum, namely [[alumina]], is quite different from [[Lime (mineral)|lime]] and [[chalk]], and is one of the ingredients in common [[clay]].<ref name=Pott-1746-Chym-Untrs/>{{efn|''Concentrirt man hingegen diese solution gelinde, und läßt sie crystallisiren, so schiessen harte und mercklich adstringente und hinter her etwas süßliche crystallen an, die allen Umständen nach in der Haupt-Sach nichts anders sind als ein formaler Alaun. Diese Entdeckung ist in der physicalischen Chymie von Wichtigkeit. Man hat bishero geglaubt, die Grund-Erde des Alauns sey eine in acido Vitrioli solvirte kalckige ... Erde,&nbsp;...''
:
:[On the other hand, if one gently concentrates this solution, and lets it crystallize, then there precipitate hard, noticeably astringent crystals with a somewhat sweet aftertaste, which in all circumstances are mainly nothing other than a form of alum. This discovery is of importance to chemistry. One had hitherto believed {{grey|[that]}} the fundamental earth of alum is a calcareous ... earth dissolved in sulfuric {{nobr|acid,&nbsp;...]}}
::: — J. H. Pott (1746)<ref name=Pott-1746-Chym-Untrs/>
}}<ref name=Marggraf-1754/>{{rp|pages=41–66}}

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.<ref name=Chisholm-1911/>{{rp|page=766}}<ref name=Marggraf-1754/>{{rp|page=31–40}} 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.<ref name=Bergman-1767/>{{efn|
After acknowledging that Marggraf had noticed that potash caused alum to crystallize from a solution of alumina and sulfuric acid, Bergman adds
:''"Notatu quoque dignum est, quod hoc cristallisationis obstaculum alcali volatili aeque tollatur, non vero alkali minerali et calce."''
::[It is significant as well that by {{grey|[use of]}} the volatile alkali (''i.e., ammonia'') this obstacle to crystallization is similarly removed, but not {{grey|[in the cases of]}} mineral alkali]
::(''i.e., sodium carbonate and lime'').
:::— Bergman (1767)<ref name=Bergman-1767/>}}<ref name=Chisholm-1911/>{{rp|page=766}}

The composition of common alum was determined finally by [[Louis Nicolas Vauquelin|Louis Vauquelin]] in 1797. As soon as [[Martin Heinrich Klaproth|Martin Klaproth]] discovered the presence of potassium in [[leucite]] and [[lepidolite]],<ref name=Klaproth-1797/><ref name=Klaproth-1801/>{{efn|"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 ... This constituent part of leucite ... is no other than ''pot-ash'', which, hitherto, has been thought ''exclusively'' to belong to the ''vegetable kingdom'', and has, on this account, been called ''vegetable alkali''.
:
This discovery, which I think of great importance, cannot fail to occasion considerable changes in the systems of natural {{nobr|history, ... ." — [[Martin Heinrich Klaproth|M. H. Klaproth]] (1801)<ref name=Klaproth-1801/>}}
}}
[[Louis Nicolas Vauquelin|Vauquelin]] demonstrated that common alum is a [[double salt]], composed of sulfuric acid, alumina, and potash.<ref name=Vauquelin-1797/> In the same journal volume, [[Jean-Antoine Chaptal|Chaptal]] published the analysis of four different kinds of alum, namely, Roman alum, Levant alum, British alum, and an alum manufactured by himself,<ref name=Chaptal-1797/> confirming [[Louis Nicolas Vauquelin|Vauquelin]]'s result.<ref name="Chisholm-1911" />

==Production==
Some alums occur as minerals, the most important being [[alunite]].

The most important alums – potassium, sodium, and ammonium – are produced industrially. Typical recipes involve combining [[aluminium sulfate]] and the sulfate monovalent cation.<ref name="Helmboldt-Hudson-Misra-etal-2007-UllmannEncyc" /> The aluminium sulfate is usually obtained by treating minerals like alum [[schist]], [[bauxite]] and [[cryolite]] with sulfuric acid.<ref name="Chisholm-1911" />{{rp|page=767|}}

==Types==
[[File:Potassium alum octahedral like crystal.jpg|thumb|Crystal of potassium alum]]

Aluminium-based alums are named by the monovalent cation. Unlike the other [[alkali metal]]s, [[lithium]] does not form alums; a fact attributed to the small size of its ion.

The most important alums are
* [[Potassium alum]], {{chem|KAl(SO|4|)|2|·12 H|2|O}}, also called "potash alum" or simply "alum"
* [[Sodium aluminium sulfate|Sodium alum]], {{chem|NaAl(SO|4|)|2|·12 H|2|O}}, also called "soda alum" or "SAS"
* [[Ammonium aluminium sulfate|Ammonium alum]], {{chem|NH|4|Al(SO|4|)|2|·12 H|2|O}}

==Chemical properties==
Aluminium-based alums have a number of common chemical properties. They are soluble in [[water (molecule)|water]], have a sweetish taste, react as [[acid]] by turning blue [[litmus]] to red, and [[crystal]]lize in regular [[octahedron|octahedra]]. In alums each metal ion is surrounded by six water molecules. When heated, they liquefy, and if the heating is continued, the [[water of crystallization]] is driven off, the salt froths and swells, and at last an amorphous powder remains.<ref name=Chisholm-1911/>{{rp|page=766|}} They are [[astringent]] and acidic.

===Crystal structure===
Alums crystallize in one of three different crystal structures. These classes are called α-, β- and γ-alums. The first X-ray crystal structures of alums were reported in 1927 by [[James M. Cork]] and [[Lawrence Bragg]], and were used to develop the [[phase retrieval]] technique [[isomorphous replacement]].<ref name=Cork-1927-10-LED-Phil-Mag/>

===Solubility===
The solubility of the various alums in water varies greatly, sodium alum being soluble readily in water, while [[caesium]] and [[rubidium]] alums are only slightly soluble. The various solubilities are shown in the following table.<ref name=Chisholm-1911/>{{rp|page=767}}

At temperature {{mvar|T}}, 100&nbsp;parts water dissolve:
: {| class="wikitable" style="text-align:right;"
|-
! {{mvar|T}} !! Ammonium {{small|<br/>alum}} !! Potassium {{small|<br/>alum}} !! Rubidium {{small|<br/>alum}} !! Caesium {{small|<br/>alum}}
|-
|   0&nbsp;°C ||  2.62     ||   3.90 ||  0.71     || 0.19{{0}}
|-
|  10&nbsp;°C ||  4.50     ||   9.52 ||  1.09     || 0.29{{0}}
|-
|  50&nbsp;°C || 15.9{{0}} ||  44.11 ||  4.98     || 1.235
|-
|  80&nbsp;°C || 35.20     || 134.47 || 21.60     || 5.29{{0}}
|-
| 100&nbsp;°C || 70.83     || 357.48 || -  || - 
|}

==Uses==

=== Industrial processes ===
Aluminium-based alums have been used since antiquity, and are still important for many industrial processes. The most widely used alum is [[potassium alum]]. It has been used since antiquity as a [[Clarifying agent|flocculant]] to clarify cloudy liquids, as a [[mordant]] (or binder) in [[dyeing]], and in [[tanning (leather)|tanning]].  It is still widely used in [[water treatment]], for medicine, for cosmetics (in [[deodorant]]), for food preparation (in [[baking powder]] and [[pickling]]), and to fire-proof paper and cloth.

=== To stop bleeding ===
Alum is used as a [[styptic]] (to stop bleeding) in styptic pencils available from pharmacists. Alum blocks, available from barber shops and gentlemen's outfitters, are used to stem bleeding from shaving nicks;<ref name="Blake-Blade-2020-01-11-shaving-Alum" /> and as an [[astringent]]. 

Powdered alum are also used in Southeast Asian traditional medicine for open wounds and sores.<ref name="Chaudhury-Rafei-2001" /><ref name="Emocling-c2018" />

=== Deodorant ===
[[File:Tawas (alum), a traditional deodorant in the Philippines 01.jpg|thumb|{{lang|tl|Tawas}} (powdered alum crystals), a traditional scent-less [[deodorant]] for underarm and feet odor in the [[Philippines]] and most of [[Island Southeast Asia]]]]

An alum block can be used directly as a perfume-free deodorant (antiperspirant), and unprocessed mineral alum is sold in Indian bazaars for that purpose. Throughout [[Island Southeast Asia]], potassium alum is most widely known as ''tawas'' and has numerous uses. It is used as a traditional antiperspirant and deodorant. The crystals are usually ground into a fine powder before use.<ref name="Chaudhury-Rafei-2001" /><ref name="Emocling-c2018" />{{Better source needed|reason=The cited sources are insufficient: <ref name="Chaudhury-Rafei-2001" /> is a WHO report on alternative medicines that only tangentially mentions tawas as a body odor reliever, and <ref name="Emocling-c2018" /> is a blog post that itself states alum or tawas "doesn't stop us from sweating." Medically backed sources on its effectiveness and safety as an antiperspirant and/or deodorant should be provided here.|date=September 2024}}

=== Bread ===
In Britain alum has been used as a way of preserving [[flour]] and bleaching it. Bakers used small amounts to make the fine white [[manchet]] bread produced for the rich. In times of poor harvest, more alum was added. In 1758 the British government banned the use of alum in bread, although some bakers continued to use it and many people continued to demand white bread adulterated with alum.<ref>{{Cite book |last=Norman |first=Jill |date=2024 |title=The English Table - Our Food Through the Ages |location=London |publisher=Reaktion Books |isbn=978 1 78914 933 3 |publication-date=2024 |page=114 }}</ref>

During the 19th century, alum was used along with other substances like [[Plaster|plaster of Paris]] to adulterate certain food products, particularly bread. It was used to make lower-grade flour appear whiter, allowing the producers to spend less on whiter flour. Because it retains water, it would make the bread heavier, meaning that merchants could charge more for it in their shops. The amount of alum present in each loaf of bread could reach concentrations that would be toxic to humans and cause chronic [[Diarrhea|diarrhoea]], which could result in the death of young children.<ref>Phillips, Suzanne, director. [https://www.youtube.com/watch?v=j9gv5528JZQ ''The Hidden Killers of the Victorian Home'']. Sterling Documentaries, 27&nbsp;Jan. 2018. Accessed 9&nbsp;Oct. 2021.</ref>

=== Textiles and paper ===
Alum is used as a mordant in traditional textiles;<ref name=Crawfurd-1856/> For traditional [[Japanese art]], alum and [[animal glue]] were dissolved in water, forming a liquid known as ''dousa'' ({{langx|ja|[[:ja:礬水|礬水]]}}), and used as an undercoat for paper [[sizing]].

=== Jewellery ===
In [[Indonesia]] and the [[Philippines]], solutions of ''tawas'', [[salt]], [[borax]], and organic pigments were used to change the color of [[gold]] ornaments.<ref name=Villegas-2004/> 

Alum in the form of [[potassium aluminium sulphate]] or [[ammonium aluminium sulfate]] in a concentrated bath of hot water is regularly used by jewelers and machinists to dissolve hardened steel drill bits that have broken off in items made of aluminum, copper, brass, gold (any karat), silver (both sterling and fine) and stainless steel. This is because alum does not react chemically to any significant degree with any of these metals, but will corrode carbon steel. When heat is applied to an alum mixture holding a piece of work that has a drill bit stuck in it, if the lost bit is small enough, it can sometimes be dissolved or removed within hours.<ref name="Lee-2013" />

===Other===
In the Philippines, alum crystals were also burned and allowed to drip into a basin of water by ''[[babaylan]]'' for [[divination]]. It is also used in other rituals in the [[animistic]] [[anito]] religions of the islands.<ref name=Dyrness-1992/><ref name=Hornedo-2000/><ref name=Mercado-1997/><ref name=Starr-1930/>

==Related compounds==
[[File:Kristall med.jpg|thumb|Chrome alum crystal]]

Many trivalent metals are capable of forming alums. The general form of an alum is {{chem|{{mvar|XY}}(|SO|4|)|2|·{{mvar|n}}{{thin space}}H|2|O}}, where {{mvar|X}} is an [[alkali metal]] or [[ammonium]], {{mvar|Y}} is a trivalent metal, and {{mvar|n}} often is 12. The most important example is [[chrome alum]], {{chem|K|Cr(SO|4|)|2|·12 H|2|O}}, a dark violet crystalline double sulfate of chromium and potassium, was used in [[Tanning (leather)|tanning]].

In general, alums are formed more easily when the alkali metal atom is larger. This rule was first stated by Locke in 1902,<ref name=Locke-1902/> who found that if a trivalent metal does not form a caesium alum, it neither will form an alum with any other alkali metal or with ammonium.

===Selenate-containing alums===
''Selenium'' or ''selenate alums'' are also known that contain [[selenium]] in place of [[sulfur]] in the [[sulfate]] anion, making [[selenate]] ({{chem|SeO|4|2-}}) instead.<ref name="Bell-Fabre-1887" /> They are strong [[oxidizing agent]]s.

===Mixed alums===
[[File:Chromium Alum - top view.jpg|thumb|Alum crystal with small amount of [[chrome alum]] to give a slight [[Violet (color)|violet]] color]]

In some cases, [[solid solution]]s of alums with different monovalent and trivalent cations may occur.

===Other hydrates===
In addition to the alums, which are dodecahydrates, double [[sulfate]]s and [[selenate]]s of univalent and trivalent cations occur with other degrees of hydration. These materials may also be referred to as alums, including the undecahydrates such as [[mendozite]] and [[kalinite]], hexahydrates such as [[guanidine|guanidinium]] {{big|[}}{{chem|CH|6|N|3|+}}{{big|]}} and [[dimethylamine|dimethylammonium]] {{big|[}}{{chem|(|C|H|3|)|2N|H|2|+}}{{big|]}} "alums", tetrahydrates such as [[goldichite]], monohydrates such as thallium plutonium sulfate and anhydrous alums ([[yavapaiite]]s). These classes include differing, but overlapping, combinations of ions.

===Other double sulfates===
A pseudo alum is a double sulfate of the typical formula {{chem|{{mvar|X}}SO|4|·{{mvar|Y}}|2|(SO|4|)|3|·22 H|2|O}}, such that
: {{mvar|X}} is a divalent metal ion, such as [[cobalt]] ([[wupatkiite]]), [[manganese]] ([[apjohnite]]), [[magnesium]] ([[pickingerite]]) or [[iron]] ([[halotrichite]] or feather alum), and {{mvar|Y}} is a trivalent metal ion.<ref name=Mindat-Halotrichite/>

Double [[sulfate]]s with the general formula {{chem|{{mvar|X}}|2|S|O|4|·{{mvar|Y}}|2|(SO|4|)|3|·24 H|2|O}} are also known, where {{mvar|X}} is a monovalent [[cation]] such as [[sodium]], [[potassium]], [[rubidium]], [[caesium]], [[thallium|thallium{{sup|I}}]], [[ammonium]], or ({{chem|N|H|4|+}}), [[methylamine|methylammonium]] ({{chem|CH|3|N|H|3|+}}), [[hydroxylamine|hydroxylammonium]] ({{chem|HO|NH|3|+}}) or [[hydrazine#Hydrazinium salts|hydrazinium]] ({{chem|N|2|H|5|+}}) and  {{mvar|Y}} is a trivalent metal ion, such as [[aluminium]], [[chromium]], [[titanium]], [[manganese]], [[vanadium]], [[iron|iron{{sup|III}}]], [[cobalt]], [[gallium]], [[molybdenum]], [[indium]], [[ruthenium]], [[rhodium]], or [[iridium]].<ref name=Greenwood-Earnshaw-1997/>
Analogous [[selenate]]s also occur. The possible combinations of univalent cation, trivalent cation, and [[anion]] depends on the sizes of the [[ion]]s.

A [[Tutton's salt|Tutton salt]] is a double sulfate of the typical formula {{chem|{{mvar|X}}|2|SO|4|·|{{mvar|Y}}|SO|4|·6H|2|O}}, where {{mvar|X}} is a monovalent cation, and {{mvar|Y}} a [[divalent]] metal ion.

Double sulfates of the composition {{chem|{{mvar|X}}|2|S|O|4|·2{{mvar|Y}}|SO|4}}, such that {{mvar|X}} is a monovalent cation and {{mvar|Y}} is a divalent metal ion are referred to as [[langbeinite]]s, after the prototypical potassium magnesium sulfate.

==See also==
{{Portal|Chemistry}}
* [[Alunite]]
* [[Gum bichromate]] – photo prints and other similar processes use alums, sometimes as [[colloid]] (gelatin, albumen) hardeners
* [[List of minerals]]

==Footnotes==
{{Notelist}}

==References==
{{Reflist|refs=

<ref name="Austin-1984-Shreves">
{{cite book
 |last=Austin |first=George T.
 |date=1984
 |title=Shreve's Chemical process industries
 |edition=5th  |page =357
 |publisher=McGraw-Hill
 |place=New York, NY
 |isbn=9780070571471
 |url=https://books.google.com/books?id=12ahTF69BAEC&q=alums&pg=PA357
}}
</ref>

<ref name="Bell-Fabre-1887">
{{cite journal
 |last=Bell |first=Chichester H.
 |date=1887
 |title=Selenium Alums
 |journal=Journal of the Chemical Society
 |volume=LII. Part&nbsp;II. |page=1014
 |department=Abstracts of chemical papers. Inorganic chemistry.
 |url=https://books.google.com/books?id=dftJAQAAMAAJ&q=selenate%20alums&pg=PA1014
 |access-date=2017-08-19
 |via=Google Books
}} – Summary by C.H. Bell of original French article by C. Fabre, below:
:
{{cite journal
 |first=Charles |last=Fabre |date=1887
 |title=Sur les aluns formés par l'acide sélénique
 |journal=[[Comptes rendus de l'Académie des sciences]]
 |volume=105 |pages=114–115
 |language=fr |id={{BHL page|26775}} |url=https://gallica.bnf.fr/ark:/12148/bpt6k3061j/f114.item
}}
</ref>

<ref name="Bergman-1767">
{{cite book
 |first=T. O. |last=Bergman |author-link=Torbern Bergman
 |date=1767
 |chapter=IX. De confectione Aluminis
 |title=Opuscula Physica et Chemica  |language=la
 |volume=1 |pages=306–307
 |place=Lipsiae (Leipzig)
 |publication-date=1788
 |publisher=Bibliopolio I.G. Mülleriano (I.G. Müller)
 |chapter-url=https://books.google.com/books?id=HcuNbkfxYQMC&pg=PA307
 |via=Google Books
}}
</ref>

<ref name="Blake-Blade-2020-01-11-shaving-Alum">
{{cite news
 |title=Alum block for shaving – when and how to use one
 |date=11 January 2020
 |website=Blake'n Blade shave shop (blakenblade.com)
 |url=https://blakenblade.com/alum-block-for-shaving-how-to-guide
 |access-date=15 January 2020
}}
</ref>

<ref name="Borgard-Brun-Picon-2005-06-07-alunMedit">
{{cite conference
 |editor1=Borgard, Philippe
 |editor2=Brun, Jean-Pierre 
 |editor3=Picon, Maurice
 |date=7–8 June 2005
 |publication-date=2015
 |title=L'alun de Mediterranée
 |place=Centre Jean Bérard, Naples, Aix-en-Provence
 |conference=Colloque International, Naples, Lipari
 |series=Collection du Centre Jean Bérard
 |volume=23
 |publication-place=Naples, IT
 |publisher=Publications du Centre Jean Bérard
 |oclc=492478586 |isbn=978-2-918887-37-9
 |language=fr,en,it,grc,gmy,es
 |quote=Histoire et archéologie des Mondes chrétiens et musulmans médiévaux" (UMR 5648 du CNRS). Textes des communications en français, anglais, italien, citations en grec ancien, mycénien, espagnol.
}}
{{Isbn|2903189846}}
{{Isbn|978-2-903189-84-6}}
— ISBNs may be muddled with a 2003 conf., same name, and 2015 publ. date is suspect.
</ref>

<ref name="Chaptal-1797">
{{cite journal
 |first=J.-A. |last=Chaptal |author-link=Jean-Antoine Chaptal
 |date=1797
 |title=Comparée des quatre principales sortes d'Alun connues dans le commerce; et Observations sur leur nature et leur usage
 |language=fr
 |journal=Annales de Chimie et de Physique
 |series=1st series  |volume=22  |pages=280–296
 |url=http://babel.hathitrust.org/cgi/pt?id=mdp.39015065209101;view=1up;seq=288
 |via=Hathi Trust Digital Library (hathitrust.org)
}}
</ref>

<ref name="Chaudhury-Rafei-2001">
{{cite book
 |last1=Chaudhury |first1=Ranjit Roy
 |last2=Rafei     |first2=Uton Muchtar
 |title=Traditional Medicine in Asia
 |date=2001
 |publisher=World Health Organization
 |location=New Delhi
 |isbn=9290222247
 |url=https://apps.who.int/iris/bitstream/handle/10665/206025/B0104.pdf?sequence
}}
</ref>

<ref name="Chisholm-1911">
{{EB1911|wstitle=Alum|volume=1|pages=766-767}} 
</ref>

<ref name="Cork-1927-10-LED-Phil-Mag">
{{Cite journal
 |last=Cork |first=J. M.
 |date=1927-10-01
 |title=LX. The crystal structure of some of the alums
 |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science
 |volume=4 |issue=23 |pages=688–698
 |doi=10.1080/14786441008564371
 |issn=1941-5982
}}
</ref>

<ref name="Crawfurd-1856">
{{cite book
 |last=Crawfurd |first=John
 |date=1856
 |title=A Descriptive Dictionary of the Indian Islands and Adjacent Countries
 |publisher=Bradbury and Evans
 |page=[https://archive.org/details/adescriptivedic00crawgoog/page/n24 11]
 |url=https://archive.org/details/adescriptivedic00crawgoog
 |via=Internet Archive (archive.org)
}}
</ref>

<ref name="Dioscor-MatMed">
{{cite book
 |first=Pedanius |last=Dioscorides |author-link=Pedanius Dioscorides
 |title=[[De Materia Medica]]
 |trans-title=On Medical Materials
 |at=book&nbsp;5, chapter&nbsp;123
 |language=el, la
}}
</ref>

<ref name="Dyrness-1992">
{{cite book
 |last=Dyrness |first=William A.
 |date=1992
 |title=Invitation to Cross-cultural Theology: Case studies in vernacular theologies
 |publisher=Zondervan
 |isbn=9780310535812
 |page=96
 |url=https://books.google.com/books?id=3OgdjmR7beAC
 |via=Google Books
}}
</ref>

<ref name="Emocling-c2018">
{{cite magazine
 |last=Emocling  |first=Oliver
 |date=c. 2018
 |title=Tawas might be the best natural deodorant, but give these brands a try
 |access-date=26 November 2019
 |magazine=Scout Magazine
 |place=Manila, Philippines
 |publisher=Hinge Inquirer Publications
 |url=https://www.scoutmag.ph/style/beauty/tawas-natural-deodorant-brands-olivere-20190205
}}
</ref>

<ref name="Goitein-Sanders-1967">
{{cite book
 |last1=Goitein |first1=Shelomo Dov
 |last2=Sanders |first2=Paula
 |date=1967
 |title=A Mediterranean Society: Daily life
 |publisher=University of California Press
 |isbn=0520048695
 |pages=405
 |url=https://books.google.com/books?id=UzOvJHFTTeUC
 |access-date=22 June 2020
}}
</ref>

<ref name="Greenwood-Earnshaw-1997">
{{cite book
 |last1=Greenwood |first1=N. N.
 |last2=Earnshaw  |first2=A.
 |name-list-style=amp
 |date=1997
 |title=Chemistry of the Elements
 |edition=2nd
 |place=Oxford, UK
 |publisher=Butterworth-Heinemann
 |isbn=0-7506-3365-4
}}
</ref>

<ref name="Helmboldt-Hudson-Misra-etal-2007-UllmannEncyc">
{{cite book
 |last1=Helmboldt |first1=Otto          |last2=Hudson |first2=L. Keith
 |last3=Misra   |first3=Chanakya        |last4=Wefers |first4=Karl
 |last5=Heck    |first5=Wolfgang        |last6=Stark  |first6=Hans
 |last7=Danner  |first7=Max             |last8=Rösch  |first8=Norbert
 |date=2007
 |edition=electronic
 |section=Aluminum compounds, inorganic
 |title=Ullmann's Encyclopedia of Industrial Chemistry
 |pages=a01_527.pub2 |publisher=Wiley-VCH
 |place=Weinheim, DE
 |doi=10.1002/14356007.a01_527.pub2
 |isbn=9783527306732 |url=https://epdf.pub/ullmanns-encyclopedia-of-industrial-chemistry-electronic-release-2007.html
 |access-date=2021-08-29  |postscript=,
}}
{{Isbn|978-352730385-4}} (print),
{{Isbn|978-352730673-2}} (online).
</ref>

<ref name="Herodotus-c430ʙᴄᴇ-Hists">
{{cite book
 |author=[[Herodotus]]
 |date=n.d. |orig-date=c.&nbsp;430&nbsp;BCE
 |script-title=el:Ἱστορίαι
 |title=Historíai̯
 |trans-title=[[Histories (Herodotus)|The Histories]]
 |at=2.180
}}
</ref>

<ref name="Hornedo-2000">
{{cite book
 |last=Hornedo |first=Florentino H.
 |title=Taming the Wind: Ethno-cultural history on the Ivatan of the Batanes Isles
 |date=2000
 |publisher=University of Santo Tomas Publishing House
 |location=Manila, Philippines
 |isbn=9789715061230
 |pages=197–203
}}
</ref>

<ref name="InvivoGen-Alum-adjvt">
{{cite web
 |title=Alhydrogel 
 |series=Alum vaccine adjuvant for research
 |website=InvivoGen
 |date=25 November 2016
 |access-date=2018-06-08
 |url=https://www.invivogen.com/alhydrogel
}}
</ref>

<ref name="Klaproth-1797">
{{cite book
 |first=M. H. |last=Klaproth |author-link=Martin Heinrich Klaproth
 |date=1797
 |title=Beiträge zur Chemischen Kenntniss Der Mineralkörper
 |language=de
 |trans-title=Contributions to our Chemical Knowledge of Minerals
 |publisher=Decker and Co., [[Poznań|Posen]]; Heinrich August Rottmann, Berlin
}}
{{cite book
 |title=pp.&nbsp;45–46
 |publisher = Bei Decker ... ; Bei Heinrich August Rottmann
 |url=https://babel.hathitrust.org/cgi/pt?id=nyp.33433066422746;view=1up;seq=65
}}
&
{{cite book
 |title=p.&nbsp;193
 |publisher = Bei Decker ... ; Bei Heinrich August Rottmann
 |url=https://babel.hathitrust.org/cgi/pt?id=nyp.33433066422746;view=1up;seq=213
 |via=Hathi Trust Digital Library (hathitrust.org)
}}
</ref>

<ref name="Klaproth-1801">
{{cite book
 |first=M. H. |last=Klaproth |author-link=Martin Heinrich Klaproth
 |date=1801
 |title=Analytical Essays Towards Promoting the Chemical Knowledge of Mineral Substances
 |publisher=T. Cadell, Jr. & W. Davies
 |place=London, UK
}}
{{cite web
 |title=pp.&nbsp;353–354
 |date=1801
|url=https://archive.org/stream/analyticalessay01klapgoog#page/n374/mode/2up
}}
&
{{cite web
 |title=p.&nbsp;472
 |date=1801
 |url=https://archive.org/stream/analyticalessay01klapgoog#page/n494/mode/2up
 |via=Internet Archive (archive.org)
}}
</ref>

<ref name="Lee-2013">
{{cite book
 |first=Nancy |last=Lee
 |date=6 August 2013
 |title=The Complete Idiot's Guide to Making Metal Jewelry
 |page=114
 |publisher=DK
 |isbn=978-1-61564-370-7
 |url=https://books.google.com/books?id=DZscAAAAQBAJ&pg=PT114
}}
</ref>

<ref name="Locke-1902">
{{cite journal
 |first=J. |last=Locke
 |year = 1902
 |title = On some double suphates of thallic thallium and caesium
 |journal = American Chemical Journal
 |volume = 27 | pages = 281
}}
</ref>

<ref name="Marggraf-1754">
{{cite journal
 |last=Marggraf |first=Andreas Sigismund 
 |date=1754
 |title=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
 |language=fr
 |trans-title=Experiments that concern the regeneration of alum from its own earth, after having separating it by sulfuric acid; with some artificial compounds of alum by means of other earths and the aforesaid acid
 |journal=Mémoires de l'Académie des sciences et belles-lettres de Berlin
 |pages=31–66
 |publisher=Deutsche Akademie der Wissenschaften zu Berlin
 |url=http://babel.hathitrust.org/cgi/pt?id=nyp.33433009864186;view=1up;seq=41
 |via=Hathi Trust Digital Library (hathitrust.org)
}}
</ref>

<ref name="Mercado-1997">
{{cite book
 |last=Mercado |first=Leonardo N.
 |title=Doing Filipino Theology
 |date=1997
 |publisher=Divine Word Publications
 |isbn=9789715101035
 |page=30
}}
</ref>

<ref name="Mindat-Halotrichite">
{{cite web
 |title=Halotrichite
 |website=Mindat.org
 |place=Keswick, Virginia
 |publisher=Hudson Institute of Mineralogy
 |url=http://www.mindat.org/min-1809.html
}}
</ref>

<ref name="PlinySr-NatHist">
{{cite book
 |author=Gaius Plinius Secundus |author-link=Pliny the Elder
 |orig-year=c. 79 |date=n.d.
 |title=Naturalis Historia
 |trans-title=[[Natural History]]
 |chapter=Alumen, and the several varieties of it; Thirty-eight remedies
 |at=book&nbsp;35, chapter&nbsp;52
 |language=la, en
 |publisher=[[Tufts University]]
 |department=Perseus Digital Library
 |chapter-url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.02.0137%3Abook%3D35%3Achapter%3D52
 |access-date=27 December 2011
}}
</ref>

<ref name="Pott-1746-Chym-Untrs">
{{cite book
 |first=Johann Heinrich |last=Pott
 |date=1746
 |url=https://books.google.com/books?id=uxZAAAAAcAAJ&pg=PA32
 |via=Google Books
 |title=Chymische Untersuchungen, welche fürnehmlich von der Lithogeognosia oder Erkäntniß und Bearbeitung der gemeinen einfacheren Steine und Erden ingleichen von Feuer und Licht handeln
 |language=de
 |trans-title=Chemical investigations which primarily concern lithogeognosia or knowledge and processing of common simple rocks and earths as well as fire and light
 |place=[[Potsdam]], [[Germany|DE]]
 |publisher=Christian Friedrich Voss
 |volume=1 |page=32
}}
</ref>

<ref name="Stahl-1703">
{{cite book
 |last=Stahl |first=G. E.
 |date=1703
 |title=Specimen Beccherianum
 |publisher=Johann Ludwig Gleditsch
 |place=[[Leipzig]], DE
 |page=269
 |url=http://www.e-rara.ch/zut/content/pageview/4572022
}}
</ref>

<ref name="Stahl-1723">
{{cite book
 |first=George Ernst |last=Stahl
 |date=1723
 |chapter=XXXII |page=305&nbsp;ff
 |title=Ausführliche Betrachtung und zulänglicher Beweiß von den Talken daß dieselbe aus einer zarten Erde mit Wasser innig verbunden bestehen 
 |language=de
 |quote=In Berlegung des Wänsenhauses
 |chapter-url=https://books.google.com/books?id=nvVlAAAAcAAJ&pg=PA305
}}
</ref>

<ref name="Starr-1930">
{{cite book
 |last=Starr |first=Frederick
 |date=1930
 |title=Some Filipino Beliefs
 |publisher=W. Glaisher
 |page=75
 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015024649074
 |via=Hathi Trust Digital Library (hathitrust.org)
}}
</ref>

<ref name="Vauquelin-1797">
{{cite journal
 |last=Vauquelin |first=L. N. |author-link=Louis Nicolas Vauquelin
 |date=1797
 |title=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
 |language=fr
 |journal=Annales de Chimie et de Physique
 |series=1st series |volume=22 |pages=258–279
 |via=Hathi Trust Digital Library (hathitrust.org)
 |url=http://babel.hathitrust.org/cgi/pt?id=mdp.39015065209101;view=1up;seq=266
}}
</ref>

<ref name="Villegas-2004">
{{cite book
 |last=Villegas |first=Ramon N.
 |date=2004
 |title=Ginto: History wrought in gold
 |publisher=Bangko Sentral ng Pilipinas, The Gold Collection
 |page=67
}}
</ref>

}} <!-- end "refs=" -->

==External links==
{{Wiktionary}}
* {{Commons category-inline|Alum}}

{{Authority control}}

[[Category:Double salts|*]]
[[Category:Astringent flavors]]
[[Category:Dyeing]]
[[Category:Food additives]]
[[Category:Sulfates]]
[[Category:Sulfate minerals]]
[[Category:Traditional medicine]]