Calcium oxide is called quicklime. It is prepared by heating the lime stone in a rotatory kiln at 1070-1270 K.

CO₂ formed escapes and hence the above equilibrium shifts towards the formation of calcium oxide. 
When rain-water falls on quick lime, slaked lime is formed.

It is used:
(i) in the preparation of cement, glass and calcium carbide. 
(ii) in the purification of sugar
(iii) in drying alcohol and non-acidic gases like ammonia etc.,
(iv) in softening of hard water. 
(v) as a flux in the extraction of metals. 
(vi) in agriculture as a fertiliser, disinfectant and germicide.

(i) Caustic soda
It is used:
(a) in the manufacture of sodium metal, soap (from oils and fats), rayon, paper, dyes and drugs,
(b) for mercerising cotton to make cloth unshrinkable.

(ii) Sodium carbonate
It is used:
(a) in laundries and in softening of water as washing soda,
(b) in the manufacture of glass, caustic soda, soap powders etc.
(iii) Quick lime
It is used:
(a) in the purification of sugar and in the manufacture of dyestuffs,
(b) in the manufacture of bleaching powder, slaked lime and lime colours.