The namealum is also used, more generally, for salts with the same formula and structure, except that aluminium is replaced by anothertrivalent metal ion likechromiumIII, or sulfur is replaced by anotherchalcogen likeselenium.[1] The most common of these analogs ischrome alumKCr(SO 4) 2·12 H 2O.
In most industries, the namealum (orpapermaker's alum) is used to refer toaluminium sulfate,Al 2 (SO 4) 3·nH 2O, which is used for most industrialflocculation[1]: 766 (the variablen is an integer whose size depends on the amount of water absorbed into the alum). Formedicine, the wordalum may also refer toaluminium hydroxide gel used as avaccine adjuvant.[2]
The western desert of Egypt was a major source of alum substitutes in antiquity. Theseevaporites were mainlyFeAl 2(SO 4) 4·22 H 2O,MgAl 2(SO 4) 4·22 H 2O,NaAl(SO 4) 2·6 H 2O,MgSO 4·7H 2O andAl 2(SO 4) 3·17 H 2O.[3][4]TheAncient GreekHerodotus mentions Egyptian alum as a valuable commodity inThe Histories.[5]
The production of potassium alum fromalunite is archaeologically attested on the islandLesbos.[6]The site was abandoned during the 7th century CE, but dates back at least to the 2nd century CE. Nativealumen from the island ofMelos appears to have been a mixture mainly of alunogen (Al 2(SO 4) 3·17 H 2O) with potassium alum and other minor sulfates.[7]
By comparing Pliny's description with the account ofstypteria (στυπτηρία) given byDioscorides,[9] it is obvious the two are identical. Pliny informs us that a form ofalumen was found naturally in the earth, and terms itsalsugoterrae.
Pliny wrote that different substances were distinguished by the name ofalumen, but they were all characterised by a certain degree ofastringency, and were all employed for dyeing and medicine. Pliny wrote that there is another kind of alum that the ancientGreeks termschiston, and which "splits into filaments of a whitish colour".[8] From the nameschiston and the mode of formation, it seems that this kind was the salt that forms spontaneously on certain salty minerals, as alumslate and bituminousshale, and consists mainly of sulfates of iron and aluminium.[citation needed] One kind ofalumen was a liquid, which was apt to be adulterated; but when pure it had the property of blackening when added topomegranate juice. This property seems to characterize asolution ofironII 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. Thealumen of the ancients, then, was not always potassium alum, not even an alkali aluminum sulfate.[10]: 766–767
Alum andgreen vitriol (iron sulfate) both have sweetish and astringent taste, and they had overlapping uses. Therefore, through theMiddle Ages, alchemists and other writers do not seem to have distinguished the two salts accurately. In the writings of thealchemists we find the wordsmisy,sory, andchalcanthum applied to either compound; and the nameatramentum sutorium, which one might expect to belong exclusively to green vitriol, applied indiscriminately to both.[citation needed]
Alum was the most commonmordant (substance used to set dyes on fabrics) used by the dye industry, especially in Islamic countries, during themiddle ages. It was the main export of theChad region, from where it was transported to the markets ofEgypt andMorocco, and then toEurope. Less significant sources were found in Egypt andYemen.[11]
Marggraf also showed that perfect crystals with properties of alum can be obtained by dissolving alumina insulfuric acid and addingpotash orammonia to the concentrated solution.[10]: 766 [15]: 31–40 In 1767,Torbern Bergman observed the need for potassium or ammonium sulfates to convertaluminium sulfate into alum, while sodium or calcium would not work.[16][d][10]: 766
The composition of common alum was determined finally byLouis Vauquelin in 1797. As soon asMartin Klaproth discovered the presence of potassium inleucite andlepidolite,[17][18][e]Vauquelin demonstrated that common alum is adouble salt, composed of sulfuric acid, alumina, and potash.[19] In the same journal volume,Chaptal published the analysis of four different kinds of alum, namely, Roman alum, Levant alum, British alum, and an alum manufactured by himself,[20] confirmingVauquelin's result.[10]
Some alums occur as minerals, the most important beingalunite.
The most important alums – potassium, sodium, and ammonium – are produced industrially. Typical recipes involve combiningaluminium sulfate and the sulfate monovalent cation.[21] The aluminium sulfate is usually obtained by treating minerals like alumschist,bauxite andcryolite with sulfuric acid.[10]: 767
Aluminium-based alums are named by the monovalent cation. Unlike the otheralkali metals,lithium does not form alums; a fact attributed to the small size of its ion.
The most important alums are
Potassium alum,KAl(SO 4) 2·12 H 2O, also called "potash alum" or simply "alum"
Sodium alum,NaAl(SO 4) 2·12 H 2O, also called "soda alum" or "SAS"
Aluminium-based alums have a number of common chemical properties. They are soluble inwater, have a sweetish taste, react asacid by turning bluelitmus to red, andcrystallize inregular octahedra. In alums each metal ion is surrounded by six water molecules. When heated, they liquefy, and if the heating is continued, thewater of crystallization is driven off, the salt froths and swells, and at last an amorphous powder remains.[10]: 766 They areastringent and acidic.
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 byJames M. Cork andLawrence Bragg, and were used to develop thephase retrieval techniqueisomorphous replacement.[22]
The solubility of the various alums in water varies greatly, sodium alum being soluble readily in water, whilecaesium andrubidium alums are only slightly soluble. The various solubilities are shown in the following table.[10]: 767
Aluminium-based alums have been used since antiquity, and are still important for many industrial processes. The most widely used alum ispotassium alum. It has been used since antiquity as aflocculant to clarify cloudy liquids, as amordant (or binder) indyeing, and intanning. It is still widely used inwater treatment, for medicine, for cosmetics (indeodorant), for food preparation (inbaking powder andpickling), and to fire-proof paper and cloth.
Alum is used as astyptic (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;[23] and as anastringent.
Powdered alum are also used in Southeast Asian traditional medicine for open wounds and sores.[24][25]
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. ThroughoutIsland Southeast Asia, potassium alum is most widely known astawas and has numerous uses. It is used as a traditional antiperspirant and deodorant. The crystals are usually ground into a fine powder before use.[24][25][better source needed]
In Britain alum has been used as a way of preservingflour and bleaching it. Bakers used small amounts to make the fine whitemanchet 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.[26]
During the 19th century, alum was used along with other substances likeplaster 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 chronicdiarrhoea, which could result in the death of young children.[27]
Alum is used as a mordant in traditional textiles;[28] For traditionalJapanese art, alum andanimal glue were dissolved in water, forming a liquid known asdousa (Japanese:礬水), and used as an undercoat for papersizing.
Alum in the form ofpotassium aluminium sulphate orammonium 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.[30]
In the Philippines, alum crystals were also burned and allowed to drip into a basin of water bybabaylan fordivination. It is also used in other rituals in theanimisticanito religions of the islands.[31][32][33][34]
Many trivalent metals are capable of forming alums. The general form of an alum isXY(SO 4) 2·nH 2O, whereX is analkali metal orammonium,Y is a trivalent metal, andn often is 12. The most important example ischrome alum,KCr(SO 4) 2·12 H 2O, a dark violet crystalline double sulfate of chromium and potassium, was used intanning.
In general, alums are formed more easily when the alkali metal atom is larger. This rule was first stated by Locke in 1902,[35] 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.
In addition to the alums, which are dodecahydrates, doublesulfates andselenates of univalent and trivalent cations occur with other degrees of hydration. These materials may also be referred to as alums, including the undecahydrates such asmendozite andkalinite, hexahydrates such asguanidinium[CH 6N+ 3] anddimethylammonium[(CH 3)2NH+ 2] "alums", tetrahydrates such asgoldichite, monohydrates such as thallium plutonium sulfate and anhydrous alums (yavapaiites). These classes include differing, but overlapping, combinations of ions.
ATutton salt is a double sulfate of the typical formulaX 2SO· 4YSO 4·6H 2O, whereX is a monovalent cation, andY adivalent metal ion.
Double sulfates of the compositionX 2SO 4·2YSO 4, such thatX is a monovalent cation andY is a divalent metal ion are referred to aslangbeinites, after the prototypical potassium magnesium sulfate.
^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, ...
[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[that] the fundamental earth of alum is a calcareous ... earth dissolved in sulfuricacid, ...]
^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[use of] the volatile alkali (i.e., ammonia) this obstacle to crystallization is similarly removed, but not[in the cases of] mineral alkali]
^"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 thanpot-ash, which, hitherto, has been thoughtexclusively to belong to thevegetable kingdom, and has, on this account, been calledvegetable alkali.
This discovery, which I think of great importance, cannot fail to occasion considerable changes in the systems of naturalhistory, ... ." —M. H. Klaproth (1801)[18]
^"Alhydrogel".InvivoGen. Alum vaccine adjuvant for research. 25 November 2016. Retrieved2018-06-08.
^Picon, M.; et al. (2005).L'alun des oasis occidentales d'Egypte: Researches sur terrain et recherches en laboratoire.
^abcBorgard, Philippe; Brun, Jean-Pierre; Picon, Maurice, eds. (7–8 June 2005). Written at Centre Jean Bérard, Naples, Aix-en-Provence.L'alun de Mediterranée. Colloque International, Naples, Lipari. Collection du Centre Jean Bérard (in French, English, Italian, Ancient Greek, Mycenaean Greek, and Spanish). Vol. 23. Naples, IT: Publications du Centre Jean Bérard (published 2015).ISBN978-2-918887-37-9.OCLC492478586.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.ISBN2903189846ISBN978-2-903189-84-6— ISBNs may be muddled with a 2003 conf., same name, and 2015 publ. date is suspect.
^abStahl, George Ernst (1723)."XXXII".Ausführliche Betrachtung und zulänglicher Beweiß von den Talken daß dieselbe aus einer zarten Erde mit Wasser innig verbunden bestehen (in German). p. 305 ff.In Berlegung des Wänsenhauses
^abBergman, T. O. (1767)."IX. De confectione Aluminis".Opuscula Physica et Chemica (in Latin). Vol. 1. Lipsiae (Leipzig): Bibliopolio I.G. Mülleriano (I.G. Müller) (published 1788). pp. 306–307 – via Google Books.
^Klaproth, M. H. (1797).Beiträge zur Chemischen Kenntniss Der Mineralkörper [Contributions to our Chemical Knowledge of Minerals] (in German). Decker and Co.,Posen; Heinrich August Rottmann, Berlin.pp. 45–46. Bei Decker ... ; Bei Heinrich August Rottmann.&p. 193. Bei Decker ... ; Bei Heinrich August Rottmann – via Hathi Trust Digital Library (hathitrust.org).
^abKlaproth, M. H. (1801).Analytical Essays Towards Promoting the Chemical Knowledge of Mineral Substances. London, UK: T. Cadell, Jr. & W. Davies."pp. 353–354". 1801.&"p. 472". 1801 – via Internet Archive (archive.org).
^Cork, J. M. (1927-10-01). "LX. The crystal structure of some of the alums".The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science.4 (23):688–698.doi:10.1080/14786441008564371.ISSN1941-5982.
^Hornedo, Florentino H. (2000).Taming the Wind: Ethno-cultural history on the Ivatan of the Batanes Isles. Manila, Philippines: University of Santo Tomas Publishing House. pp. 197–203.ISBN9789715061230.
^Mercado, Leonardo N. (1997).Doing Filipino Theology. Divine Word Publications. p. 30.ISBN9789715101035.
^Starr, Frederick (1930).Some Filipino Beliefs. W. Glaisher. p. 75 – via Hathi Trust Digital Library (hathitrust.org).
^Locke, J. (1902). "On some double suphates of thallic thallium and caesium".American Chemical Journal.27: 281.
^Bell, Chichester H. (1887)."Selenium Alums". Abstracts of chemical papers. Inorganic chemistry.Journal of the Chemical Society. LII. Part II.: 1014. Retrieved2017-08-19 – via Google Books. – Summary by C.H. Bell of original French article by C. Fabre, below:
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