permanent hardness is particularly objectionable in water for boiler purposes, as it forms scale.
permanent hardness is caused by other compounds of lime that are not precipitated by boiling the water.
permanent hardness is caused by calcium sulphate which is soluble in 400 parts of water and cannot be removed by boiling.
The total hardness of water is therefore commonly made up of temporary and permanent hardness.
The hardness of water may be of two kinds,— temporary hardness and permanent hardness.
Boiling the water does not affect these salts; hence such waters are said to have permanent hardness.