Alum

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Name Variations

 * aluminum potassium sulfate
 * ammonium aluminum sulphate
 * potassium aluminum phosphate

About Alum
Wikipedia Article About Alum on Wikipedia

Alum, in chemistry, is a term given to the crystallized double sulfates of the typical formula M+2SO4·M3+2(SO4)3·24H2O, where M+ is the sign of an alkali metal (lithium, sodium, potassium, rubidium, or caesium), and M3+ denotes one of the trivalent metal ions (typically aluminium, chromium, or iron (III)). The ammonium ion (NH4+) also occurs in the M+ position.

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.


 * 1) Alum powder, found in the spice section of many grocery stores, may be used in pickling recipes as a preservative to maintain fruit and vegetable crispness.
 * 2) Alum is used as the acidic component of some commercial baking powders.
 * 3) Alum was used by bakers in England during the 1800s to make bread whiter. White bread was demanded by the middle class. In 1875, the Sale of Food and Drugs Act prevented this and other adulterations.