stand by soil,
mould, earth, &c. are composed. These, however, though forming nearly
all of the solid portions of the world, are constantly mixed with
foreign matters, as metals, (particularly iron,) and acids, (as
carbonic acid.)

What are the properties of Silex?

Silex, or pure flint, will not dissolve in water, nor can it be melted
by itself in any heat; but combined with alkalies, as soda or potash,
it forms glass. It is the principal ingredient of most of the precious
stones.

What are the chief uses of Silex?

It is the most durable article for the formation of roads; a necessary
ingredient in earthenware, porcelain, and cements; and the principal
material of glass and vitreous substances. The making of pastes or
artificial gems is a branch of the art of glass-making; the basis used
is a very hard and pure silex.

_Basis_, that part of any mixture which is the ground or
base; the first principle or element of a substance.

Describe the properties of Lime.

It is of a white color, and possesses a hot, caustic taste. It forms
peculiar salts with acids; changes vegetable blues to green; will not
fuse; gives out a quantity of caloric when united with water; and
absorbs carbonic acid when exposed to air. Lime is very useful in the
arts and manufactures, in medicine, &c. The farmers use it as manure
to fertilize land.

_Caustic_, burning, corroding: a term applied to substances
which eat away and burn any thing with which they are
brought in contact.

In what state is Lime found in nature?

Never native, but combined with other substances;--generally with an
acid, and most plentifully with carbonic acid, as in chalk, marble,
&c. It is also found in vegetables, and is the basis of animal bones;
it likewise occurs in the water of the ocean, and in that of all
springs and rivers. The method of procuring _lime_, from chalk,
marble, limestone, oyster-shells, &c., has already been described in a
former chapter.

What are the properties of Clay?

Argil, or pure clay, also called _alumina_, from its being the basis
of alum, is soft to the touch, adhesive, and emits a peculiar odor
when moistened;--forms a paste with water, and hardens in the fire.
Its uses are so various and important, that it would have been almost
impossible for man to have attained his present degree of
civilization, if it had not been given him by nature in such
abundance. Its uses have already been desc