15. Material nouns may be used as class names. Instead of
considering the whole body of material of which certain uses are made,
one can speak of particular uses or phases of the substance; as--

(1) _Of individual objects_ made from metals or other substances
capable of being wrought into various shapes. We know a number of
objects made of iron. The material _iron_ embraces the metal contained
in them all; but we may say, "The cook made the _irons_ hot,"
referring to flat-irons; or, "The sailor was put in _irons_" meaning
chains of iron. So also we may speak of _a glass_ to drink from or to
look into; _a steel_ to whet a knife on; _a rubber_ for erasing marks;
and so on.

(2) _Of classes_ or _kinds_ of the same substance. These are the same
in material, but differ in strength, purity, etc. Hence it shortens
speech to make the nouns plural, and say _teas_, _tobaccos_, _paints_,
_oils_, _candies_, _clays_, _coals_.

(3) _By poetical use_, of certain words necessarily singular in idea,
which are made plural, or used as class nouns, as in the following:--

The lone and level _sands_ stretch far away.--SHELLEY.

From all around--
Earth and her _waters_, and the depths of air--
Comes a still voice.--BRYANT.

Their airy ears
_The winds_ have stationed on the mountain peaks.