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Crystal of potassium alum, KAl(SO 4) 2 ·12H 2 O. An alum (/ ˈ æ l ə m /) is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula X Al(SO 4) 2 ·12 H 2 O, such that X is a monovalent cation such as potassium or ammonium. [1] By itself, "alum" often refers to potassium alum, with the ...
Alum-(K) is a hydrous potassium aluminium sulfate mineral with formula KAl(SO 4) 2 ·12(H 2 O). It is the mineral form of potassium alum and is referred to as potassium alum in older sources. It is a member of the alum group. [2] It occurs as colorless to white, soft isometric crystals and efflorescence coatings. [3]
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 X Al(SO 4 ) 2 ·12H 2 O , where X is a monovalent cation such as potassium or ammonium .
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 (NH 4)Al(SO 4) 2 ·12H 2 O. It is used in small amounts in a variety of niche applications.
The ancients are known to have used alum as a dyeing mordant and for city defense. [75] After the Crusades, alum, an indispensable good in the European fabric industry, [76] was a subject of international commerce; [77] it was imported to Europe from the eastern Mediterranean until the mid-15th century. [78] The nature of alum remained unknown.
Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound first mentioned under various Sanskrit names in Ayurvedic medicinal texts such as charak samhita, sushrut samhita, and ashtang hridaya; is chemically defined as the double sulfate of potassium and aluminium, with chemical formula KAl(SO 4) 2.
Ammonium iron(III) sulfate, NH 4 Fe(SO 4) 2 ·12 H 2 O, or NH 4 [Fe(H 2 O) 6](SO 4) 2 ·6 H 2 O, also known as ferric ammonium sulfate (FAS) or iron alum, is a double salt in the class of alums, which consists of compounds with the general formula AB(SO 4) 2 · 12 H 2 O. [2] It has the appearance of weakly violet, octahedrical crystals.
Wulff construction. The surface free energy is shown in red, with in black normals to lines from the origin to .The inner envelope is the Wulff shape, shown in blue. The Wulff construction is a method to determine the equilibrium shape of a droplet or crystal of fixed volume inside a separate phase (usually its saturated solution or vapor).