An alum (/ˈæləm/) is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula XAl(SO
2O, where X is a monovalent cation such as potassium or ammonium. By itself, "alum" often refers to potassium alum, with the formula KAl(SO
2O. 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 trivalent metal ion like chromium(III), and/or sulfur is replaced by other chalcogen like selenium. The most common of these analogs is chrome alum KCr(SO
In some industries, the name "alum" (or "papermaker's alum") is used to refer to aluminium sulfate Al
2O. Most industrial flocculation done with "alum" actually uses aluminium sulfate. In medicine, "alum" may also refer to aluminium hydroxide gel used as a vaccine adjuvant.
The western desert of Egypt was a major source of alum substitutes in antiquity. These evaporites were mainly FeAl
2O and Al
The production of potassium alum from alunite is archaeologically attested on the island Lesbos. This site was abandoned in the 7th century but dates back at least to the 2nd century CE. Native alumen from the island of Melos appears to have been a mixture mainly of alunogen (Al
2O) with potassium alum and other minor sulfates.
By comparing Pliny's description with the account of stupteria given by Dioscorides, it is obvious the two are identical. Pliny informs us that a form of alumen was found naturally in the earth, and calls it salsugoterrae.
Pliny wrote that different substances were distinguished by the name of alumen, but they were all characterised by a certain degree of astringency, and were all employed in dyeing and medicine. Pliny says that there is another kind of alum that the Greeks call schiston, and which "splits into filaments of a whitish colour", From the name schiston and the mode of formation, it appears that this kind was the salt that forms spontaneously on certain salty minerals, as alum slate and bituminous shale, and consists chiefly of sulfates of iron and aluminium. 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 of iron 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.
Alum and green vitriol (iron sulfate) both have sweetish and astringent taste, and they a had overlapping uses. Therefore, through the Middle Ages, alchemists and other writers do not seem to have discriminated the two salts accurately from each other. In the writings of the 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 indifferently to both.
In the early 1700s, Georg Ernst Stahl claimed that reacting sulfuric acid with limestone produced a sort of alum. The error was soon corrected by Johann Pott and Andreas Marggraf, who showed that the precipitate obtained when an alkali is poured into a solution of alum, namely alumina, is quite different from lime and chalk, and is one of the ingredients in common clay.
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. 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.
The composition of common alum was finally determined by Louis Vauquelin in 1797. As soon as Martin Klaproth discovered the presence of potassium in leucite and lepidolite, Vauquelin demonstrated that common alum is a double salt, composed of sulfuric acid, alumina, and potash. 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, confirming Vauquelin's result.
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. The aluminium sulfate is usually obtained by treating minerals like alum schist, bauxite and cryolite with sulfuric acid.
The most important alums are
Aluminium-based alums have a number of common chemical properties. They are soluble in water, have a sweetish taste, react acid to litmus, and crystallize in regular 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. They are astringent and acidic.
Alums crystallize in one of three different crystal structures. These classes are called α-, β- and γ-alums.
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:
|T||Ammonium alum||Potassium alum||Rubidium alum||Caesium alum|
Aluminium-based alums have been used since antiquity, and are still important in many industrial processes.
The most widely used alum is potassium alum. It was used since antiquity as a flocculant to clarify turbid liquids, as a mordant in dyeing, and in tanning. It is still widely used in the treatment of water, in medicine, for cosmetics (in deodorant), in food preparation (in baking powder and pickling), and to fire-proof paper and cloth.
Sodium alum is used in substitution to potassium alum in baking powders. Ammonium alum has a few niche uses. Other alums have mostly research interest.
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) and silver (both sterling and fine). This is because alum does not react chemically to any significant degree with any of these metals, but will corrode 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 / removed within hours.
Many trivalent metals are capable of forming alums. The general form of an alum is XM(SO4)2·nH2O, where X is an alkali metal or ammonium, M is a trivalent metal, and n often is 12. The most important example is chrome alum, KCr(SO
2O, a dark violet crystalline double sulfate of chromium and potassium, was used in tanning.
In general, alums are formed more easily when the alkali metal atom is larger. This rule was first stated by Locke in 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.
In some cases, solid solutions of alums with different monovalent and trivalent cations may occur.
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 guanidinium (CH
3) and dimethylammonium ((CH
2) "alums", tetrahydrates such as goldichite, monohydrates such as thallium plutonium sulfate and anhydrous alums (yavapaiites). These classes include differing, but overlapping, combinations of ions.
A pseudo alum is a double sulfate of the typical formula ASO
2O, 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.
Double sulfates with the general formula A
2O are also known, where A is a monovalent cation such as sodium, potassium, rubidium, caesium, or thallium(I), or a compound cation such as ammonium (NH+
4), methylammonium (CH
3), hydroxylammonium (HONH+
3) or hydrazinium (N
5), B is a trivalent metal ion, such as aluminium, chromium, titanium, manganese, vanadium, iron(III), cobalt(III), gallium, molybdenum, indium, ruthenium, rhodium, or iridium. Analogous selenates also occur. The possible combinations of univalent cation, trivalent cation, and anion depends on the sizes of the ions.
Double sulfates of the composition A
4, where A is a univalent cation and B is a divalent metal ion are referred to as langbeinites, after the prototypical potassium magnesium sulfate.
The 2007 Alum Rock earthquake occurred on October 30 at 8:04 p.m. Pacific Daylight Time in Alum Rock Park in San Jose, California. It measured 5.6 on the moment magnitude scale and had a maximum Mercalli intensity of VI (Strong). The event was then the largest in the San Francisco Bay Area since the 1989 Loma Prieta earthquake, which measured 6.9 on the moment magnitude scale, but was later surpassed by the 2014 South Napa earthquake. Ground shaking from the Alum Rock quake reached San Francisco and Oakland and other points further north. Sixty thousand felt reports existed far beyond Santa Rosa, as far north as Eugene, Oregon.Adjuvant
An adjuvant is a pharmacological or immunological agent that modifies the effect of other agents. Adjuvants may be added to a vaccine to boost the immune response to produce more antibodies and longer-lasting immunity, thus minimizing the dose of antigen needed. Adjuvants may also be used to enhance the efficacy of a vaccine by helping to modify the immune response to particular types of immune system cells: for example, by activating T cells instead of antibody-secreting B cells depending on the purpose of the vaccine. Adjuvants are also used in the production of antibodies from immunized animals. There are different classes of adjuvants that can push immune response in different directions, but the most commonly used adjuvants include aluminum hydroxide and paraffin oil.Alam Hajji Baqeri
Alam Hajji Baqeri (Persian: علم حاجي باقري, also Romanized as ‘Alam Ḩājjī Bāqerī, ‘Alam-e Ḩājjī Bāqer, ‘Alam-e Ḩājjī Bāqerī, and ‘Alam Ḩājī Bāqerī; also known as Alam-e Hājī Bāqer, Deh ‘Alam, and Deh Alum) is a village in Chupanan Rural District, Anarak District, Nain County, Isfahan Province, Iran. At the 2006 census, its existence was noted, but its population was not reported.Alum Bay
Alum Bay is a bay near the westernmost point of the Isle of Wight, England, within close sight of the Needles rock formation. Of geological interest and a tourist attraction, the bay is noted for its multi-coloured sand cliffs. The waters and adjoining seabed form part of the Needles Marine Conservation Zone and the shore and heath above are part of the Headon Warren and West High Down Site of Special Scientific Interest.Alum Creek, West Virginia
Alum Creek is a census-designated place (CDP) in Kanawha and Lincoln counties along the Coal River in the U.S. state of West Virginia. It had a population of 1,749 at the 2010 census.The community was named after nearby Alum Creek.Alum Creek State Park
Alum Creek State Park is a 4,630-acre (1,870 ha) Ohio state park in Delaware County, Ohio, in the United States. Alum Creek Lake was constructed from 1970 to 1974 as part of the Flood Control Act of 1962. Alum Creek Dam was constructed on Alum Creek, a tributary of Big Walnut Creek, which drains into the Scioto River. Alum Creek Reservoir holds 3,387 acres (1,371 ha) of water and is open to fishing, boating, ice fishing, ice boating and swimming. The park is just north of the state capital of Columbus and contains the remnants of a settlement by freed slaves that arrived in Ohio from North Carolina.Alum Rock, Birmingham
Alum Rock (known locally as "The Rock") is an inner-city suburb of Birmingham, England, located roughly 2 miles east of Birmingham city centre. The area is officially a division of Saltley. Rockwood Academy is a secondary school located in the area.Alum Rock, San Jose
Alum Rock () is a neighborhood and census-designated place in San Jose, California, in East San Jose. The CDP, which excludes all annexed areas, had a population of 15,536 at the 2010 census. It is home to Alum Rock Park, the oldest municipal park in California and one of the largest in the United States.
Formerly a separate town, much of the community is unincorporated surrounded by incorporated San Jose; neighborhoods between White Road and Capitol Avenue are part of a city/county agreement for annexation. James Lick High School, Mt. Pleasant High School, and William C. Overfelt High School (which are part of the East Side Union High School District), Joseph George Middle School, Ocala Middle School, and other schools in the Alum Rock Union School District serve the neighborhood. Near the center of the community is a small neighborhood commercial strip along Alum Rock Avenue at White Road.Alum Rock Park
Alum Rock Park, in the Alum Rock district of San Jose, California, is California's oldest municipal park, founded in 1872. Located in a valley in the Diablo Range foothills on the east side of San Jose, the 720 acre (2.9 km2) park offers 13 miles (21 km) of trails, varying from fairly level along Penitencia Creek to sharp switchbacks climbing to the ridges to the South Rim Trail and the North Rim Trail. The narrow floor of the valley includes a visitor center, a small museum/animal rehab facility, picnic areas, playgrounds, lawns, sand volleyball pits, mineral springs, lush plant life, woodlands, creek play opportunities, and occasional group camping.
The ridge trails offer views of Santa Clara Valley and of the valley in which the park is located. Some trails in the park are a part of the Bay Area Ridge Trail; the Todd Quick trail connects with the Santa Clara Valley Open Space Authority's 1,600-acre Sierra Vista Open Space Preserve.
Equestrians and mountain bikers have access to some of the park's trails, while others are reserved for hikers only. Cross-country teams from high schools around North San Jose, such as James Lick High School and Independence High, use the park for training and for meets.Alum Rock Transit Center
Alum Rock Transit Center is a light rail and bus station operated by Santa Clara Valley Transportation Authority (VTA). This station is served by VTA's Alum Rock–Santa Teresa line.
The station was opened in 2004 as part of VTA's Capitol light rail extension.Alum Rock station
Alum Rock/28th Street station is a proposed underground Bay Area Rapid Transit station in the Little Portugal neighborhood of San Jose, California. It would be located north of East Santa Clara Street between North 28th Street and U.S. Route 101, behind Five Wounds Portuguese National Church. Preceded by the Berryessa/North San Jose BART station, it would be the first station of the Phase II portion of the Silicon Valley BART extension. The station would have direct service to Santa Clara, Richmond, and San Francisco/Daly City. The proposed station is named after Alum Rock, a neighborhood to the northeast.Alum Rock–Santa Teresa (VTA)
Alum Rock–Santa Teresa is a light rail route operated by Santa Clara Valley Transportation Authority (VTA). The Alum Rock–Santa Teresa route is one of three existing VTA light rail routes. The other two light rail routes are the Mountain View–Winchester line and the Ohlone/Chynoweth–Almaden line. On system maps, the line is represented as the Blue Line, however VTA primarily uses its name and Line 901 in their documents.Alum Springs, West Virginia
Alum Springs is a ghost town in Greenbrier County, West Virginia, United States. Alum Springs was 2 miles (3.2 km) east of Maxwelton. Alum Springs appeared on USGS maps as late as 1923.Aluminium sulfate
Aluminium sulfate is a chemical compound with the formula Al2(SO4)3. It is soluble in water and is mainly used as a coagulating agent (promoting particle collision by neutralizing charge) in the purification of drinking water and waste water treatment plants, and also in paper manufacturing.
The anhydrous form occurs naturally as a rare mineral millosevichite, found e.g. in volcanic environments and on burning coal-mining waste dumps. Aluminium sulfate is rarely, if ever, encountered as the anhydrous salt. It forms a number of different hydrates, of which the hexadecahydrate Al2(SO4)3•16H2O and octadecahydrate Al2(SO4)3•18H2O are the most common. The heptadecahydrate, whose formula can be written as [Al(H2O)6]2(SO4)3•5H2O, occurs naturally as the mineral alunogen.
Aluminium sulfate is sometimes called alum or papermaker's alum in certain industries. However, the name "alum" is more commonly and properly used for any double sulfate salt with the generic formula XAl(SO4)2·12H2O, where X is a monovalent cation such as potassium or ammonium.Ammonium aluminium sulfate
Ammonium aluminium sulfate, also known as ammonium alum or just alum (though there are many different substances also called "alum"), is a white crystalline double sulfate usually encountered as the dodecahydrate, formula (NH4)Al(SO4)2·12H2O. It is used in small amounts in a variety of niche applications. The dodecahydrate occurs naturally as the rare mineral tschermigite.Hex key
A hex key, Allen wrench or Allen key, is a tool used to drive bolts and screws with hexagonal sockets in their heads.
The Allen name is a registered trademark, originated by the Allen Manufacturing Company of Hartford, Connecticut circa 1910, and currently owned by Apex Tool Group, LLC. Its genericised use is discouraged by this company. The standard generic name used in catalogues and published books and journals is "hex key".Potassium alum
Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound: the double sulfate of potassium and aluminium, with chemical formula KAl(SO4)2. It is commonly encountered as the dodecahydrate, KAl(SO4)2·12H2O. It crystallizes in cubic structure with space group P a -3 and lattice parameter of 12.18 Å. The compound is the most important member of the generic class of compounds called alums, and is often called simply alum.Potassium alum is commonly used in water purification, leather tanning, dyeing, fireproof textiles, and baking powder as E number E522. It also has cosmetic uses as a deodorant, as an aftershave treatment and as a styptic for minor bleeding from shaving.Santa Clara Valley Transportation Authority light rail
VTA Light Rail (reporting mark SCCT) is a light rail system serving San Jose, California and its suburbs in Silicon Valley. It is operated by the Santa Clara Valley Transportation Authority, or VTA, and consists of 42.2 miles (67.9 km) of network comprising two main lines and a spur line on standard gauge tracks. Originally opened in 1987, the light rail system has gradually expanded since then, and currently has 62 light rail stations in operation on the three lines. VTA operates a fleet of 99 Kinki Sharyo Low Floor Light Rail Vehicles (LFLRV) to service its passengers. The system's average weekday daily ridership as of Q3 2018 is 28,800 passengers; the greatest daily average recorded over a month was 37,536 in June 2008.Sodium aluminium sulfate
Sodium aluminium sulfate is the inorganic compound with the chemical formula NaAl(SO4)2·12H2O (sometimes written Na2SO4·Al2(SO4)3·24H2O). Also known as soda alum, sodium alum, or SAS, this white solid is used in the manufacture of baking powder and as a food additive.