Alum
Alum is both a specific chemical compound and a class of chemical compounds.
- It means potassium aluminium sulfate, a chemical compound.
- It also means a double sulfate salt.

Chrome alum, chromium potassium sulfate
Examples:
- Potash alum is potassium aluminum sulfate
- Sodia alum is sodium aluminum sulfate
- Ammonium alum is ammonium aluminum sulfate
History
Words like "alum" and "potash" were used before modern chemistry developed. The word 'alumen' occurs in Pliny's Natural History (23–79 AD). In the 52nd chapter of his 35th book, he gives a detailed description. Different substances were distinguished by the name of 'alumen', but they were all astringents,[1] and were all used in dyeing and medicine.
Notes
- Astringent: causes body tissue to shrink or contract.
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