Alum
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2008-07-16T16:47:16Z
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/* Early uses in industry */
:''For '''alum''' meaning "graduate," see [[Alumnus]].''
{{wiktionary}}
[[Image:Alum.jpg|thumb|200px|right|A crystal of alum]]
'''Alum''', ({{IPAEng|ˈæləm}}) refers to a specific [[chemical compound]] and a class of chemical compounds. The specific compound is the hydrated aluminum potassium sulfate with the [[chemical formula|formula]] KAl(SO<sub>4</sub>)<sub>2</sub><sup>.</sup>12H<sub>2</sub>O. The class of compounds known as alums have the related [[stoichiometry]], AB(SO<sub>4</sub>)<sub>2</sub><sup>.</sup>12H<sub>2</sub>O.
==Crystal chemistry of the alums==
Double [[sulfate]]s with the general formula A<sub>2</sub>SO<sub>4</sub>·B<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>·24H<sub>2</sub>O, are known where A is a monovalent [[cation]] such as [[sodium]], [[potassium]], [[rubidium]], [[caesium]], or [[thallium|thallium(I)]], or a compound cation such as [[ammonium]] (NH<sub>4</sub><sup>+</sup>), [[methylamine|methylammonium]](CH<sub>3</sub>NH<sub>3</sub><sup>+</sup>), [[hydroxylamine|hydroxylammonium]] (HONH<sub>3</sub><sup>+</sup>) or [[hydrazine#Hydrazinium_salts|hydrazinium]] (N<sub>2</sub>H<sub>5</sub><sup>+</sup>), B is a trivalent metal ion, such as [[aluminium]], [[chromium]], [[titanium]], [[manganese]], [[vanadium]], [[iron|iron (III)]], [[cobalt|cobalt(III)]], [[gallium]], [[molybdenum]], [[indium]], [[ruthenium]], [[rhodium]] or [[iridium]].<ref>Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.</ref> The specific combinations of univalent cation, trivalent cation and [[anion]] depends on the sizes of the [[ion]]s. For example, unlike the other [[alkali metal]]s the small [[lithium]] ion does not form alums, and there is only one sodium alum. In some case [[solid solution]]s of alums occur.
Alums crystallise in one of three different crystal structures. These classes are called α-, β- and γ-alums.
==Applications==
Alums are useful for a range of industrial processes. They are soluble in [[water (molecule)|water]]; have an [[astringent]], acid, and sweetish taste; react [[acid]] to [[litmus]]; and [[crystal]]lize in regular [[octahedron|octahedra]]. 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.
[[Potassium alum]] is the common alum of commerce, although [[soda alum]], [[ferric alum]], and [[ammonium alum]] are manufactured.
[[Aluminium sulfate]] is sometimes called alum in informal contexts, but this usage is not regarded as technically correct. Its properties are quite different from those of the set of alums formally described above.
==Alchemical and later discoveries and uses==
The presence of [[sulfuric acid]] in potassium alum was known to the [[Alchemy|alchemists]], since the time of the [[Alchemy and chemistry in Islam|Arabian alchemist]], [[Geber|Jabir ibn Hayyan]] (Geber), who discovered sulfuric acid in the 8th century.<ref name=Hassan-Chemical>{{cite web |url= http://www.history-science-technology.com/Articles/articles%2072.htm |title=Technology Transfer in the Chemical Industries |accessdate=2008-03-29 |last=Hassan |first=Ahmad Y |authorlink=Ahmad Y Hassan |work=History of Science and Technology in Islam }}</ref> A thousand years later in the 18th century, J. H. Pott and [[Andreas Sigismund Marggraf]] demonstrated that [[alumina]] was another constituent. Pott in his ''Lithogeognosia'' showed that the [[precipitation (chemistry)|precipitate]] obtained when an alkali is poured into a [[solution]] of alum is quite different from [[lime (mineral)|lime]] and chalk, with which it had been confounded by [[Georg Ernst Stahl|G.E. Stahl]]. Marggraf showed that alumina is one of the constituents of alum, but that this earth possesses peculiar properties, and is one of the ingredients in common [[clay]]. He also showed that crystals of alum cannot be obtained by dissolving alumina in sulfuric acid and evaporating the solutions, but when a solution of [[potash]] or [[ammonia]] is dropped into this liquid, it immediately deposits perfect crystals of alum.
[[Torbern Bergman]] also observed that the addition of potash or ammonia made the solution of alumina in sulfuric acid crystallize, but that the same effect was not produced by the addition of soda or of [[Lime (mineral)|lime]], and that potassium sulfate is frequently found in alum.
After [[Martin Heinrich Klaproth|M.H. Klaproth]] had discovered the presence of potassium in [[leucite]] and [[lepidolite]], it occurred to [[Louis Nicolas Vauquelin|L.N. Vauquelin]] that it was probably an ingredient likewise in many other [[mineral]]s. Knowing that alum cannot be obtained in crystals without the addition of potash, he began to suspect that this alkali constituted an essential ingredient in the salt, and in 1797 he published a dissertation demonstrating that alum is a [[double salt]], composed of sulfuric acid, alumina, and potash. Soon after, [[Jean-Antoine Chaptal|J.A. Chaptal]] published the analysis of four different kinds of alum, namely, Roman alum, Levant alum, British alum and alum manufactured by himself. This analysis led to the same result as Vauquelin.
===Pliny's writings===
The word "alumen," which we translate "alum," occurs in [[Pliny the Elder|Pliny]]'s ''Natural History''. In the 15th chapter of his 35th book he gives a detailed description of it. By comparing this with the account of stupteria given by [[Dioscorides]] in the 123rd chapter of his 5th book, it is obvious that the two are identical. Pliny informs us that alumen was found naturally in the earth. He calls it ''salsugoterrae''. Different substances were distinguished by the name of "alumen"; but they were all characterized by a certain degree of astringency, and were all employed in dyeing and medicine, the light-colored alumen being useful in brilliant dyes, the dark-colored only in dyeing black or very dark colors. One species 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 of iron [[sulfate]] in water; a solution of ordinary (potassium) alum would possess no such property. Pliny says that there is another kind of alum that the [[Ancient Greece|Greek]]s call ''schistos''. It forms in white threads upon the surface of certain stones. From the name schistos, and the mode of formation, there can be little doubt that this species was the salt which forms spontaneously on certain salty minerals, as alum [[slate]] and bituminous [[shale]], and which consists chiefly of sulfates of iron and aluminium. Possibly in certain places the iron sulfate may have been nearly wanting, and then the salt would be white, and would answer, as Pliny says it did, for dyeing bright colors. Several other species of alumen are described by Pliny, but we are unable to make out to what minerals he alludes.
The alumen of the ancients, then, was not the same as the alum of the moderns. It was most commonly an iron sulfate, sometimes probably an aluminium sulfate, and usually a mixture of the two. But the ancients were unacquainted with our alum. They were acquainted with a crystallized iron sulfate, and distinguished it by the names of misy, sory, and chalcanthum. As alum and [[Iron(II) sulfate|green vitriol]] were applied to a variety of substances in common, and as both are distinguished by a sweetish and astringent taste, writers, even after the discovery of alum, do not seem to have discriminated the two salts accurately from each other. In the writings of the [[Alchemy|alchemists]] we find the words misy, sory, chalcanthum applied to alum as well as to iron sulfate; and the name atramentum sutorium, which ought to belong, one would suppose, exclusively to green vitriol, applied indifferently to both. Various [[mineral]]s are employed in the manufacture of alum, the most important being alunite or alum-stone, alum [[schist]],
[[bauxite]] and [[cryolite]].
===Early uses in industry===
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. These sources were unreliable, however, and there was a push to develop a source in England. With state financing, attempts were made throughout the [[16th Century]], but without success until early on in the [[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]].
Alum (known as ''turti'' in local Indian languages) was also used for water treatment by Indians for hundreds of years.
==Production==
===Alum from alunite===
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. The alum schists employed in the manufacture of alum are mixtures of iron [[pyrite]], aluminium [[silicate]] and various bituminous substances, and are found in upper [[Bavaria]], [[Bohemia]], [[Belgium]], and [[Scotland]]. These are either roasted or exposed to the [[weathering]] action of the air. In the roasting process, sulfuric acid is formed and acts on the clay to form aluminium sulfate, a similar condition of affairs being produced during weathering. The mass is now systematically extracted with water, and a solution of aluminium sulfate of [[specific gravity]] 1.16 is prepared. This solution is allowed to stand for some time (in order that any calcium sulfate and basic ferric sulfate may separate), and is then evaporated until ferrous sulfate crystallizes on cooling; it is then drawn off and evaporated until it attains a specific gravity of 1.40. It is now allowed to stand for some time, decanted from any sediment, and finally mixed with the calculated quantity of potassium sulfa te (or if ammonium alum is required, with ammonium sulfate), well agitated, and the alum is thrown down as a finely-divided precipitate of alum meal. If much iron should be present in the shale then it is preferable to use potassium chloride in place of potassium sulfate.
===Alum from clays or bauxite===
In the preparation of alum from [[clay]]s or from [[bauxite]], the material is gently calcined, then mixed with sulfuric acid and heated gradually to boiling; it is allowed to stand for some time, the clear solution drawn off and mixed with acid potassium sulfate and allowed to crystallize. When [[cryolite]] is used for the preparation of alum, it is mixed with [[calcium carbonate]] and heated. By this means, sodium aluminate is formed; it is then extracted with water and [[Precipitation (chemistry)|precipitated]] either by [[sodium bicarbonate]] or by passing a current of [[carbon dioxide]] through the solution. The precipitate is then dissolved in sulfuric acid, the requisite amount of potassium sulfate added and the solution allowed to crystallize.
==Types of alum==
===[[Soda alum]]===
Sodium alum, Na<sub>2</sub>SO<sub>4</sub>·Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>·24H<sub>2</sub>O, mainly occurs in nature as the mineral [[mendozite]]. It is very soluble in water, and is extremely difficult to purify. In the preparation of this salt, it is preferable to mix the component solutions in the cold, and to evaporate them at a temperature not exceeding 60 °C. 100 parts of water dissolve 110 parts of sodium alum at 0 °C, and 51 parts at 16 °C. Soda alum is used in the acidulent of food as well as in the manufacture of baking powder.
===[[Ammonium alum]]===
Ammonia alum, NH<sub>4</sub>Al(SO<sub>4</sub>)<sub>2</sub>·12H<sub>2</sub>O, a white crystalline double sulfate of aluminium, is used in water purification, in vegetable glues, in porcelain cements, in natural deodorants (though potassium alum is more commonly used), in tanning, dyeing and in fireproofing textiles.
==Alum solubility==
The solubility of the various alums in water varies greatly, sodium alum being readily soluble in water, while [[caesium]] and [[rubidium]] alums are only sparingly soluble. The various solubilities are shown in the following table.
:At temperature ''T'', 100 parts water dissolve:
{| border="0"
|-----
!
''T''
!
Ammonium Alum
!
Potassium Alum
!
Rubidium Alum
!
Caesium Alum
|-----
| align="right" |
0 °C
| align="right" |
2.62
| align="right" |
3.90
| align="right" |
0.71
| align="right" |
0.19
|-----
| align="right" |
10 °C
| align="right" |
4.50
| align="right" |
9.52
| align="right" |
1.09
| align="right" |
0.29
|-----
| align="right" |
50 °C
| align="right" |
15.9
| align="right" |
44.11
| align="right" |
4.98
| align="right" |
1.235
|-----
| align="right" |
80 °C
| align="right" |
35.20
| align="right" |
134.47
| align="right" |
21.60
| align="right" |
5.29
|-----
| align="right" |
100 °C
| align="right" |
70.83
| align="right" |
357.48
| align="right" |
| align="right" |
|}
==Selenate containing alumns==
Alums are also known that contain selenium in place of sulfur. They are called selenium- or selenate-alums.
==Uses==
*Makeup: Alum was often used as a base in skin whiteners and treatments during the late 16th Century in the Elizabethan fashion. This is an example of a recipe:
<blockquote>
"For the Freckles which one getteth by the heat of the Sun: Take a little Allom beaten small, temper amonst it a well brayed white of an egg, put it on a milde fire, stirring it always about that it wax not hard, and when it casteth up the scum, then it is enough, wherewith anoint the Freckles the space of three dayes: if you will defend your self that you get no Freckles on the face, then anoint your face with the whites of eggs."
Christopher Wirzung, General practise of Physicke, 1654.
</blockquote>
*Shaving alum: is a powdered form of alum used as an [[astringent]] to prevent bleeding from small shaving cuts. The [[styptic pencil]]s sold for this purpose contain aluminium sulfate or potassium aluminium sulfate. Similar products are also used on animals to prevent bleeding after nail-clipping. Alum in block form (usually potassium alum) is used as an aftershave, rubbed over the wet freshly shaved face.
*Hair Stiffener: Alum was used in rock form in the 1950's to rub on the front short hair of a "crewcut". When the hair dried, it would stay up all day.
*Crystal deodorant: Alum was used in the past as a natural underarm [[deodorant]] in Europe, Mexico, Thailand where it is called Sarn-Som, the Far East and in the [[Philippines]] where it is called Tawas. It is now commercially sold for this purpose in many countries, often in a plastic case that protects the crystal and makes it resemble other non-liquid deodorants. Typically potassium alum is used.
*Alum powder, found amongst spices at most grocery stores, is used in pickling recipes as a preservative, to maintain crispness, and as an ingredient in some play dough recipes. It is also commonly cited as a home remedy or pain relief for [[canker sores]].
*Fire retardant: By soaking and then drying cloth and paper materials they can be made fireproof.
*Wax: Alum is used in the Middle East as a component in wax, compounded with other ingredients to create a hair-removal substance.
*Foamite: Alum is used to make foamite which is used in many fire extinguishers for chemical and oil fires.
*Adjuvant: Alum is used regularly as an [[Immunologic adjuvant|adjuvant]] (enhances immune response to a given immunogen when given with it) in human immunizations.
*Antibacterial agent: Alum works as a deodorant because Alum inhibits bacterial growth. This fits the definition of an antibacterial agent. Styptic pencils or Alum powder/crystals can be applied to cuts that have a mild infection.
*Flocculating agent: Alum is used to clarify water by catching the very fine suspended particles in a gel like precipitate of aluminum hydroxide. This sinks to the bottom of the containing vessel and can be removed in a variety of ways.
==Related compounds==
In addition to the alums, which are dodecahydrates, double sulfates and selenates 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]] (CH<sub>6</sub>N<sub>3</sub><sup>+</sup>) and [[dimethylamine|dimethylammonium]] (CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub><sup>+</sup>) "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.
A pseudo alum is a double sulfate of the typical formula ASO<sub>4</sub>·B<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>·22H<sub>2</sub>O, where A is a divalent metal ion, such as [[cobalt]] ([[wupatkiite]]), [[manganese]] ([[apjohnite]]), [[magnesium]] ([[pickingerite]]) or [[iron]] ([[halotrichite]] or feather alum), and B is a trivalent metal ion.
A [[Tutton's salt|Tutton salt]] is a double sulfate of the typical formula A<sub>2</sub>SO<sub>4</sub>·BSO<sub>4</sub>·6H<sub>2</sub>O, where A is a univalent cation, and B a divalent metal ion.
==In popular culture==
Gags in which someone ingests alum, either accidentally self-administered or surreptitiously administered by another, resulting in exaggerated effects, are a traditional staple of comedy. In live-action comedies, effects on the victim usually include extreme puckering of the mouth and lips and tightening of the throat. An example of this is in [[the Three Stooges]] short "[[No Census, No Feeling]]" when Curly is making a fruit punch and thinking it was sugar, puts alum in the fruit punch.
In animated cartoons, the effects are normally expanded to include extreme shrinking of the head. One example would be in the Merrie Melodies cartoon ''[[Long-Haired Hare]]'' featuring Bugs Bunny in which he plays a prank on a person by spraying liquid alum in his throat. This causes his head to shrink and his voice to squeak. (Please see the link to the cartoon for a more complete synopsis.) Also, [[Thomas Pynchon]] borrows the joke in chapter 16 of his 1963 novel ''[[V.]]'', in a scene where alum is slipped into the beer of a jazz trumpet player.
== See also ==
* [[List of minerals]]
* [[Potash alum]]
==References==
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[[Category:Salts]]
[[Category:Sulfates]]
[[Category:Sulfate minerals]]
[[Category:Traditional medicine]]
[[Category:Astringent flavors]]
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