A sulphate of aluminium and potassium (potassium alum or potash alum), or of aluminium and ammonium (ammonium alum or ammonia alum), crystallised from solution in water, B.P.; a sulphate of aluminium and potassium, U.S.P. K2A12(SO4)4.24H2O; 948.

Characters. - B.P. In colourless transparent crystalline masses, exhibiting the faces of the regular octahedron, and having an acid sweetish astringent taste.

Reactions. - Its aqueous solution gives with caustic potash or soda a white precipitate soluble in an excess of the reagent (aluminium); and an immediate precipitate with chloride of barium (sulphate).

U.S.P. Large colourless octahedral crystals, acquiring a whitish coating on exposure to air; no smell, sweet astringent taste, and acid reaction.

Impurity. - Iron.

Test. - The solution in water does not acquire a blue colour from the addition of yellow or red prussiate of potash.

Dose. - 10 to 20 grains.



Alumen exsiccatum. Glycerinum Aluminis (1 in 5).


Alumen exsiccatum.