Tod Hutchinson, age 12, of Omaha, Nebraska, for his question:

What is limewater?

Limewater is a mild, clear liquid sometimes used in cheese making, linaments and as an antidote to certain acid poisons. It also is used to detect the presence of carbon dioxide, because this gas bubbles through the clear liquid and turns it milky white. Limewater is tame, but some of its chemical ancestors are dangerously fierce. The original ingredient is limestone, alias calcium carbonate, a soluble chalky mineral in the earth's crust.
Limestone is heated in a furnace to produce calcium oxide, alias lime or quicklime. 'this highly caustic alkaline is useful for making mortar, stripping hairs from hides and decomposing garbage. But it burns living tissues. It eagerly absorbs moisture from the air and changes to a milder chemical called calcium hydroxide. Some farmers use this chalky white lime chemical to reduce acid in the soil. It may be mixed with water to make whitewash    and when diluted with more water it becomes innocent limewater.