alum


alum
alum1
/al"euhm/, n. Chem.
1. Also called potash alum, potassium alum. a crystalline solid, aluminum potassium sulfate, K2SO4·Al2(SO4)3·24H2O, used in medicine as an astringent and styptic, in dyeing and tanning, and in many technical processes.
2. one of a class of double sulfates analogous to the potassium alum, as aluminum ammonium sulfate, having the general formula R2SO4·X2(SO4)3·24H2O, where R is a univalent alkali metal or ammonium, and X one of a number of trivalent metals.
3. (not in technical use) aluminum sulfate.
[1275-1325; ME < AF < L alumen; r. OE alefne, aelifnae < OWelsh (cf. MWelsh elyf) < L alumini- (s. of alumen)]
alum2
/euh lum"/, n. Informal.
an alumna or alumnus.
[by shortening]

* * *

Inorganic compound, any of a class of hydrated double salts, usually consisting of aluminum sulfate, water of hydration (an essential part of the crystal makeup), and the sulfate of another element.

The most important alums are those of potassium sulfate (potassium alum, or potash alum, K2SO4·Al2(SO4)3·24H2O), ammonium sulfate, and sodium sulfate. Alums occur naturally in various minerals and can be prepared and purified by crystallization from their solutions. Most are white crystals with an astringent, acid taste. They are used as paper-sizing agents, flocculating agents in water treatment, mordants in dyeing, and in pickles, baking powder, fire extinguishers, and medicines.

* * *

      any of a group of hydrated double salts, usually consisting of aluminum sulfate, water of hydration, and the sulfate of another element. A whole series of hydrated double salts results from the hydration of the sulfate of a singly charged cation (e.g., K+) and the sulfate of any one of a number of triply charged cations (e.g., Al3+). Aluminum sulfate can thus form alums with sulfates of the singly charged cations of potassium, sodium, ammonium, cesium, and other elements and compounds. In similar fashion, sulfates of the triply charged cations of iron, chromium, manganese, cobalt, and other metals may take the place of aluminum sulfate. The most important alums are potassium aluminum sulfate, ammonium aluminum sulfate, and sodium aluminum sulfate. Potassium aluminum sulfate, also known as potassium alum or potash alum, has a molecular formula of K2(SO4)·Al2(SO4)3·24H2O or KAl(SO4)2·12H2O.

      Alums can easily be produced by precipitation from an aqueous solution. In producing potassium alum, for example, aluminum sulfate and potassium sulfate are dissolved in water, and then upon evaporation the alum crystallizes out of the solution. A more common production method is to treat bauxite ore with sulfuric acid and then with potassium sulfate. Ammonium alum is produced by the evaporation of a water solution containing ammonium sulfate and aluminum sulfate. It can also be obtained by treating a mixture of aluminum sulfate and sulfuric acid with ammonia. Alums occur naturally in various minerals. Potassium alum, for example, is found in the minerals kalinite, alunite, and leucite, which can be treated with sulfuric acid to obtain crystals of the alum.

      Most alums have an astringent and acid taste. They are colourless, odourless, and exist as a white crystalline powder. Alums are generally soluble in hot water, and they can be readily precipitated from aqueous solutions to form large octahedral crystals.

      Alums have many uses, but they have been partly supplanted by aluminum sulfate itself, which is easily obtainable by treating bauxite ore with sulfuric acid. The commercial uses of alums mainly stem from the hydrolysis of the aluminum ions, which results in the precipitation of aluminum hydroxide. This chemical has various industrial uses. Paper is sized, for example, by depositing aluminum hydroxide in the interstices of the cellulose fibres. Aluminum hydroxide adsorbs suspended particles from water and is thus a useful flocculating agent in water-purification plants. When used as a mordant (binder) in dyeing, it fixes dye to cotton and other fabrics, rendering the dye insoluble. Alums are also used in pickling, in baking powder, in fire extinguishers, and as astringents in medicine.

* * *


Universalium. 2010.

Look at other dictionaries:

  • Alum — unterscheidet: Alum Branch Alum Cave Branch Alum Cave Creek Alum Cave Run, ein Fluss im US Bundesstaat West Virginia Alum Creek Alum Dirt Branch, ein Fluss im US Bundesstaat Kentucky Alum Fork Alum Fork Saline River, ein Fluss im US Bundesstaat… …   Deutsch Wikipedia

  • alum — ALUM. s. m. Espece de mineral, certain suc condensé qui se trouve dans les mines. Alum de roche. alum de plume. veines, miniere d alum. alum bruslé. eau d alum. laver un livre dans de l eau d alum …   Dictionnaire de l'Académie française

  • Alum — Al um, n. [OE. alum, alom, OF. alum, F. alun, fr. L. alumen alum.] (Chem.) A double sulphate formed of aluminium and some other element (esp. an alkali metal) or of aluminium. It has twenty four molecules of water of crystallization. [1913… …   The Collaborative International Dictionary of English

  • Alum — Al um, v. t. To steep in, or otherwise impregnate with, a solution of alum; to treat with alum. Ure. [1913 Webster] || …   The Collaborative International Dictionary of English

  • alum — (n.) late 14c., whitish mineral salt used as an astringent, dye, etc., from O.Fr. alum, from L. alumen alum, lit. bitter salt, cognate with Gk. aludoimos bitter and perhaps with English ALE (Cf. ale) …   Etymology dictionary

  • alum — alum1 [al′əm] n. [ME & OFr < L alumen, alum: for IE base see ALE] 1. a double sulfate of a monovalent metal or radical (as sodium, potassium, or ammonium) with a trivalent metal (as aluminum, iron, or chromium): it is used as an astringent, as …   English World dictionary

  • Alum — Alum, Name, so v.w. Alam (s.d.), besonders bei den Großmogulen, so: 1) A. Ghir, so v.w. Aurengzeyb. 2) Schah A. I., Sohn des Vorigen, Großmogul 1707–1711. 3) A. Ghir, Großmogul 1754–1760. 4) Schah A. II., Sohn des Vorigen, Großmogul seit 1759;… …   Pierer's Universal-Lexikon

  • alum — (Ar., Mur.) m. Alumbre …   Enciclopedia Universal

  • alum — ► NOUN ▪ a crystalline compound consisting of a double sulphate of aluminium and potassium, used in dyeing and tanning. ORIGIN Latin alumen …   English terms dictionary

  • Alum — This article is about the chemical compound. For other uses, see Alum (disambiguation). Bulk alum Alum (  / …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.