s use in
building.

[Footnote 13: See Chapter XVI., article Lime.]

_Plastic_, yielding, capable of being spread out or moulded.

What do you mean by Carbon?

A simple substance, whose most common form is purified charcoal: it
is, in fact, the base of charcoal, divested of all impurities;
combined with oxygen, it forms _carbonic acid_ gas, formerly called
fixed air. It is diffused through all animal and vegetable bodies; and
may be obtained by exposing them to a red heat. In its pure,
crystallized state, it constitutes the diamond, and as graphite, is
used in making the so-called lead-pencils.[14]

[Footnote 14: See Chapter XIV., article Diamond.]

What is Oxygen?

Air, mentioned in the first chapter of this work as the gaseous
substance which composes the atmosphere, is formed by a mixture of two
distinct elements, one called Nitrogen, or Azote, the other Oxygen.
Oxygen is, therefore, an element or simple substance diffused
generally through nature, and its different combinations are essential
to animal life and combustion. It is, in fact, the most active agent
in nature, and the principle of acidity and combustion. So wholesome
and necessary is oxygen to life, that it is often called vital air.

_Agent_, an actor; a person or thing possessing the faculty
of action.

_Essential_, necessary.

What are the properties of Nitrogen or Azote?

Nitrogen is a substance also generally diffused through nature, and
particularly in animal bodies, and causes great changes in those
absorbing or exposed to it. This gas, combined with oxygen and
hydrogen, produces neither light, heat, nor combustion, but serves to
dilute the others: of itself, it is hurtful to animal life. Nitrogen
makes the principal part of the salt we call _nitre_.

What is meant by Combustion?

The decomposition of bodies by the action of fire; the union of
combustible bodies with the oxygen of the atmosphere. The greater
access the air has to a burning body, the more rapid and complete is
the process.

_Combustible_, capable of taking fire.

_Access_, the means or liberty of approach to anything.

Are all bodies equally combustible?

No; some are more so than others, and burn with a bright flame; as
wood, dry vegetables, resins, oils, fats, &c.; others with difficulty,
and without any sensible flame, as soot, coal, the ashes of plants,
&c. There are bodies, also, which are incombustible--that is,
inc