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 const.i.tutes 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 princ.i.p.al 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, incapable of taking fire, as some alkalies, earths, &c.

What is Caloric?

Caloric is that invisible agent which produces the sensation of heat.

It exists in all bodies; it is a force we are ever in want of, and thus it is hid in everything around us, and penetrates all matter, however different may be its nature or properties.

What is meant by Gas?

All highly elastic fluids are called gases. Some are salutary, but many extremely noxious, especially such as those arising from the putrefaction of animal bodies; the burning of charcoal; corrupted air at the bottom of mines, cellars, &c. The inflammable gas, which lights our streets, churches, shops, &c., is procured chiefly from coal, burnt in furnaces for the purpose the gas being pa.s.sed through metal pipes, conveyed underground to the places where the light is required: escaping at the orifice prepared for it, it is lighted when wanted, and burns with, a brilliant flame. This gas consists of hydrogen and carbon; and the oxygen of the air, combined with the hydrogen, causes light as long as hydrogen and oxygen exist and combine.

_Salutary_, wholesome, healthful.

_Noxious_, hurtful, unwholesome.

_Putrefaction_, decay.

_Orifice_, opening, hole.

[Ill.u.s.tration: DIAMOND CUTTING AND POLISHING.]

What is Hydrogen?

One of the most abundant principles in nature; one part of it, and eight of oxygen, form water. It is only met with in a gaseous form; it is also very inflammable, and is the gas called the fire-damp, so often fatal to miners; it is the chief const.i.tuent of oils, fats, spirits, &c.; and is produced by the decomposition of water.

_Const.i.tuent_, that which forms an essential part of anything.

What is Chalk?

A white fossil substance, by some reckoned a stone, but of a friable kind, which cannot, therefore, be polished as marble; by others, more properly ranked among the earths. It is of two sorts, one a hard dry chalk, used for making lime; the other a soft, unctuous kind, used in manuring land, &c. Chalk always contains quant.i.ties of flint-stone, and the fossil remains of sh.e.l.ls, coral, animal bones, marine plants, &c.; from which circ.u.mstance there can be no doubt that _chalk is the deposited mud of a former ocean_. The chemical name of chalk is carbonate of lime. It effervesces strongly with an acid.

_Effervesce_, to froth or foam up.

_Deposited_, placed on anything.

Where is Chalk found?

In large beds or strata in the earth. Chalk, on account of its abundance in England, forms an important feature in the scenery and geology of that country; it causes the whiteness of its sea-cliffs.

Scotland and Wales are entirely without chalk. The white chalk is found, with interruptions, over a s.p.a.ce above eleven hundred miles long, extending from the north of Ireland, through England, France, Belgium, Germany, Poland, and Southern Russia, to the Crimea, with a breadth of more than eight hundred miles. The Island of Crete, now called Candia, situated in the Mediterranean, was formerly noted for its chalk. This substance is very useful in many of the arts and manufactures.

Where is the Crimea?

The peninsula of the Crimea is a part of Russia, lying on the Black Sea, by which it is bounded on the west and south.

Are there any other kinds of this earth besides the common white chalk?

Yes; there are various kinds of chalk, distinguished by their different colors, as white, black, red, &c., found in various parts of the world, of great use to the painter, both in oil and water colors, and for drawing on paper, &c.

What is Marble?

A kind of stone remarkable for its hardness and firm grain, and for being susceptible of the finest polish. It is dug in great ma.s.ses from pits or quarries; and is much used in ornamental buildings, and for statues, altars, tombs, chimney-pieces, &c. The word is derived from the French _marbre_, marble. Marble is supposed to be formed, deep within the bowels of the earth, from a loose and porous carbonate of lime, subjected to enormous heat and pressure.

_Susceptible_, easily admitting anything additional.

_Porous_, full of holes, or interstices.

Are there different sorts of this Stone?