An Elementary Study of Chemistry | Page 5

properties, no chemical action having taken place
when they were brought together.
~Chemical compounds.~ If iron filings and powdered sulphur are
thoroughly ground together in a mortar, a yellowish-green substance
results. It might easily be taken to be a new body; but as in the case of
the iron and salt, the ingredients can readily be separated. A magnet
draws out the iron. Water does not dissolve the sulphur, but other
liquids do, as, for example, the liquid called carbon disulphide. When
the mixture is treated with carbon disulphide the iron is left unchanged,
and the sulphur can be obtained again, after filtering off the iron, by
evaporating the liquid. The substance is, therefore, a mechanical
mixture.
If now a new portion of the mixture is placed in a dry test tube and
carefully heated in the flame of a Bunsen burner, as shown in Fig. 3, a
striking change takes place. The mixture begins to glow at some point,
the glow rapidly extending throughout the whole mass. If the test tube
is now broken and the product examined, it will be found to be a hard,
black, brittle substance, in no way recalling the iron or the sulphur. The
magnet no longer attracts it; carbon disulphide will not dissolve sulphur
from it. It is a new substance with new properties, resulting from the
chemical union of iron and sulphur, and is called iron sulphide. Such
substances are called chemical compounds, and differ from mechanical
mixtures in that the substances producing them lose their own
characteristic properties. We shall see later that the two also differ in

that the composition of a chemical compound never varies.
[Illustration: Fig. 3]
DEFINITION: A chemical compound is a substance the constituents of
which have lost their own characteristic properties, and which cannot
be separated save by a chemical change.
~Elements.~ It has been seen that iron sulphide is composed of two
entirely different substances,--iron and sulphur. The question arises, Do
these substances in turn contain other substances, that is, are they also
chemical compounds? Chemists have tried in a great many ways to
decompose them, but all their efforts have failed. Substances which
have resisted all efforts to decompose them into other substances are
called elements. It is not always easy to prove that a given substance is
really an element. Some way as yet untried may be successful in
decomposing it into other simpler forms of matter, and the supposed
element will then prove to be a compound. Water, lime, and many
other familiar compounds were at one time thought to be elements.
DEFINITION: An element is a substance which cannot be separated
into simpler substances by any known means.
~Kinds of matter.~ While matter has been grouped in three classes for
the purpose of study, it will be apparent that there are really but two
distinct kinds of matter, namely, compounds and elements. A
mechanical mixture is not a third distinct kind of matter, but is made up
of varying quantities of either compounds or elements or both.
~Alchemy.~ In olden times it was thought that some way could be
found to change one element into another, and a great many efforts
were made to accomplish this transformation. Most of these efforts
were directed toward changing the commoner metals into gold, and
many fanciful ways for doing this were described. The chemists of that
time were called alchemists, and the art which they practiced was
called alchemy. The alchemists gradually became convinced that the
only way common metals could be changed into gold was by the
wonderful power of a magic substance which they called the

philosopher's stone, which would accomplish this transformation by its
mere touch and would in addition give perpetual youth to its fortunate
possessor. No one has ever found such a stone, and no one has
succeeded in changing one metal into another.
~Number of elements.~ The number of substances now considered to
be elements is not large--about eighty in all. Many of these are rare, and
very few of them make any large fraction of the materials in the earth's
crust. Clarke gives the following estimate of the composition of the
earth's crust:
Oxygen 47.0% Calcium 3.5% Silicon 27.9 Magnesium 2.5 Aluminium
8.1 Sodium 2.7 Iron 4.7 Potassium 2.4 Other elements 1.2%
A complete list of the elements is given in the Appendix. In this list the
more common of the elements are marked with an asterisk. It is not
necessary to study more than a third of the total number of elements to
gain a very good knowledge of chemistry.
~Physical state of the elements.~ About ten of the elements are gases at
ordinary temperatures. Two--mercury and bromine--are liquids. The
others are all solids, though their melting points vary through wide
limits, from cæsium which melts at