Lime, Or Calcium Oxide is made by burning lime stone (calcium carbonate) which is a mineral of common occurence. It is found in the bones of all animals, shells and as marble, coral, chalk, and in other more or less familiar forms. Its uses are varied and well-known in the form of burnt lime, as calcium carbonate, and as chalk or whiting, which is an earthy form of the carbonate usually containing clay.

Burnt lime moistened with water, slacks with great violence. When slacked, one part of water to three parts of lime, it forms a soft white powder, hydrated calcium oxide. If unsufficient water is used the powder will be gritty and harsh. After slacking, a thin cream can be made by the addition of more water. Mortar is a mixture of sand with a thin cream of lime. The use of lime as whitewash is well known.

Hydraulic cement is composed of burnt lime, containing a large percentage of clay or silica, lime having the property of hardening under water in the presence of more than 10 per cent. of silica in its composition. Lime water is used in some forms of fresco painting on plaster. Slacked lime has good covering qualities and this property and its cheapness has impelled many experiments and attempts to use lime as a pigment in oil paints combined with lead, zinc and other whites. Its use in appreciable quantity, because of its alkalinity, destroys the binding quality of the oil, and leaves the paint to perish.