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
washing purposes.
Note: 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 sodium carbonate.