Hard"ness, n. [AS. heardness.]
1. The quality or state of being hard, literally
The habit of authority also had given his manners some
peremptory hardness. Sir W. Scott.
2. (Min.) The cohesion of the
particles on the surface of a body, determined by its capacity to
scratch another, or be itself scratched; -- measured among minerals
on a scale of which diamond and talc form the extremes.
3. (Chem.) The peculiar quality
exhibited by water which has mineral salts dissolved in it. Such
water forms an insoluble compound with soap, and is hence unfit for
☞ This quality is caused by the presence of calcium
carbonate, causing temporary hardness which can be removed by
boiling, or by calcium sulphate, causing permanent hardness
which can not be so removed, but may be improved by the addition of