To the chemist, all forms of matter are mere combinations of elements.
Chemical analysis is a process of separating, dividing, and subdividing
matter. When the chemist separates or analyzes compounds, until he can
no longer simplify or subdivide them, he calls these simple products
"chemical elements."
[Sidenote: Common elements]
Many of the chemical elements are well known, such as copper, iron, and
gold. Other elements that are still more common are unknown in their
elementary form, because they combine with other elements so readily
that they exist in nature only as compounds. For example: Hydrogen,
united with oxygen, forms water; the elements chlorin and sodium,
combined or united, form common salt.
[Sidenote: Number of elements]
Altogether chemists have discovered about eighty-four elements, many of
which are rare, and do not occur in common substances.
All substances of the earth, whether dead or living, are formed of
chemical elements. These elements may be found in the pure or elementary
state, or they may be mixed with other substances, or they may be
combined chemically. Copper, iron, and gold are elements in the pure
state. If we should take iron and copper filings and mix them together,
we would still have copper and iron. Were we to take copper and gold and
melt them together, we would have a metal that would be neither copper
nor gold. It would be harder than one and softer than the other. But
this substance would still be a mixture, and its properties half way
between copper and gold.
[Sidenote: Examples of chemical changes]
If a piece of iron be exposed to dampness it will soon become covered
with a reddish powder called "rust." The rusting of iron is a process of
chemical changes in which the original substance was wholly changed by
chemically uniting with the oxygen and the moisture of the atmosphere,
which is really a process of combustion. The burning of wood, the
rusting of iron, the souring of milk, and the digestion of food are, in
a way, all mere examples of chemical changes.
[Sidenote: Difference between chemical compounds and simple mixtures]
Care should be exercised to distinguish chemical compounds from simple
mixtures. Air is not a compound, but a mixture of oxygen, hydrogen and
nitrogen gases. Water, however, is a compound of oxygen and hydrogen.
Both salt and sugar are compounds, but if we grind them together,
we do not have a new compound, but a mixture of two compounds. Most
of the common things around us are mixtures of different compounds
or substances. Rocks are mixtures of many different compounds. Wood
is, likewise, formed of many different substances. Wheat contains
water, starch, cellulose, and many other compounds. Grinding the wheat
into flour does not change it chemically, but if we heat the flour
in an oven, some of the starch is changed into dextrin. The starch
has disappeared, and dextrin, a new substance, appears in its place.
Whenever elements are combined into compounds, or compounds broken up
into elements, or changed into other compounds, we have true chemical
action.
[Sidenote: Names of elements--how derived]
The names of the elements are formed in many different ways. The name
chlorin is derived from a Greek word meaning _greenish-yellow_, as
this is the color of chlorin. Bromin comes from a Greek word meaning
_a stench_, a prominent characteristic of bromin being its bad odor.
Hydrogen is formed from two Greek words, one of which means _water_ and
the other to _produce_, signifying that it enters into the composition
of water. Potassium is an element found in potash, and sodium in soda,
etc.
[Sidenote: Symbols of elements--how derived]
For convenience, abbreviations are used for the names of elements
and compounds. Thus, instead of oxygen, we may write simply "O"; for
hydrogen, "H"; for nitrogen, "N," etc. Very frequently the first letter
of the name of the element is used as the symbol. If the names of two or
more elements begin with the same letter, some other letter of the name
is added. In some cases the symbols are derived from the Latin names of
the elements. Thus, the symbol of iron is Fe, from _ferrum_; of copper,
Cu, from _cuprum_.
The following table gives the names of the elements which it will be
necessary to understand in pursuing this work.
Aluminum Al
Arsenic As
Boron B
Bromin Br
Calcium Ca
Carbon C
Chlorin Cl
Chromium Cr
Copper Cu
Fluorin F
Gold Au
Hydrogen H
Iodin I
Iron Fe
Lead Pb
Magnesium Mg
Mercury Hg
Nickel Ni
Nitrogen N
Oxygen O
Phosphorus P
Platinum Pt
Potassium K
Silicon Si
Silver Ag
Sodium Na
Sulfur S
Tin Sn
Zinc Zn