Alum

For alum meaning "graduate," see Alumn.

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Alum, in chemistry, is a term given to the crystallized double sulfates of the typical formula M2SO4·MIII2(SO4)3·24H2O, where M is the sign of an alkali metal (lithium, sodium, potassium, rubidium, caesium, or francium), and MIII denotes one of the trivalent metals (aluminium, chromium, or ferric iron). These salts are employed in dyeing and various other industrial processes. They are soluble in water; have an astringent, acid, and sweetish taste; react acid to litmus; and crystallize in regular 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.

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Potash alum is the common alum of commerce, although both soda alum and ammonium alum are manufactured.

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Chemistry: Chemistry (in Greek: χημεία) is the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. In the study of matter, chemistry also investigates its interactions with energy and itself (se...

Sulfate: Sulfate is the IUPAC name for the SO42- ion, consisting of a central sulfur atom single bonded to four tetrahedrally oriented oxygen atoms. This anion has a net negative two electric charge....

Lithium: : This article is about the chemical element Lithium. For other uses, see Lithium (disambiguation)....