permanent hardness

noun

chem hardness of water that cannot be removed by boiling as it results mainly from the presence of calcium and magnesium chlorides and sulphates

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The total hardness of water is therefore commonly made up of temporary and permanent hardness.

Boiling the water does not affect these salts; hence such waters are said to have permanent hardness.

The hardness of water may be of two kinds,— temporary hardness and permanent hardness.

Calcium sulphate, or gypsum, on the other hand, imparts permanent hardness.

Permanent hardness is caused by other compounds of lime that are not precipitated by boiling the water.

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