Lime is also added to sewage to remove phosphates. The pretreatment of water supplies involves the use lime to decrease the acidity, to soften, and to clear drinking water. A variety of other industrial processes also make extensive use of lime. It is used as an opacifier in plastics. In the refining of sugar, lime causes coagulation of plant material, allowing it to be more easily separated from the sugar syrup.
Calcium oxide no longer produces the limelight in theaters.
The theatrical use of lime has disappeared, leaving only its name, suggesting the romance of a bygone era. Because lime has a very high melting point, it can be heated to a very high temperature without melting. Substances with such high melting points can be heated to white heat, a temperature so high that the light they emit is white. Before the advent of electric lighting, white stage lighting was produced by heating lime in the flame of a torch, and this light was called limelight.