Lime Calcium hydroxide or lime is a chemical compound with the chemical formula Ca (OH)2. It is variously known as slaked lime, hydrated lime, or pickling lime. It is obtained when calcium oxide (lime or quicklime) is mixed or soaked in water. It can also be precipitated by mixing an aqueous solution of calcium chloride and an aqueous solution of sodium hydroxide. The natural, mineral form is known as portlandite rarely found from some volcanic, plutonic and metamorphic rocks. Naturally it is a colourless crystal or white powder. The physical characteristics are given below:

Appearance white
Physical State white crystals or powder, Odorless
Melting Point 580 C
Boiling Point Decompose
Specific Gravity 2.24
Solubility in Water 0.185 g/100 cc
pH 12 - 12.5
Vapor Density 2.5

A suspension of fine calcium hydroxide particles in water is called milk of lime. The solution is called limewater and is a medium strength base that reacts violently with acids and attacks many metals in presence of water. Calcium hydroxide is used in the preparation of limewater, to make milk of lime for white washing, remove temporary hardness in water softening, in agricultural practice to neutralize the acidity of the soil, manufacture of bleaching powder and also in construction (plaster, cement, lime paints, white wash).

Besides inorganic calcium carbonate, burning shells of clam can produce organic lime. Regarding quality, the organic variety is much more superior. In our country lime is used as an ingredient in betel chewing. Production of lime by heating limestones has been a Cottage Industry since British period in Chatak upazila of Sunamganj district. [Sanzida Murshed]