An Elementary Study of Chemistry | Page 4

its energy the energy is not destroyed but is
transferred to another body or system of bodies. Just as energy cannot
be destroyed, neither can it be created. If one body gains a certain
amount of energy, some other body has lost an equivalent amount.
These facts are summed up in the law of conservation of energy which
may be stated thus: While energy can be changed from one form into
another, it cannot be created or destroyed.
~Transformations of energy.~ Although energy can neither be created
nor destroyed, it is evident that it may assume many different forms.
Thus the falling water may turn the electric generator and produce a
current of electricity. The energy lost by the falling water is thus
transformed into the energy of the electric current. This in turn may be
changed into the energy of motion, as when the current is used for
propelling the cars, or into the energy of heat and light, as when it is
used for heating and lighting the cars. Again, the energy of coal may be
converted into energy of heat and subsequently of motion, as when it is
used as a fuel in steam engines.
Since the energy possessed by coal only becomes available when the
coal is made to undergo a chemical change, it is sometimes called
chemical energy. It is this form of energy in which we are especially
interested in the study of chemistry.
~Matter.~ Matter may be defined as that which occupies space and
possesses weight. Like energy, matter may be changed oftentimes from
one form into another; and since in these transformations all the other
physical properties of a substance save weight are likely to change, the
inquiry arises, Does the weight also change? Much careful
experimenting has shown that it does not. The weight of the products

formed in any change in matter always equals the weight of the
substances undergoing change.
~Law of conservation of matter.~ The important truth just stated is
frequently referred to as the law of conservation of matter, and this law
may be briefly stated thus: Matter can neither be created nor destroyed,
though it can be changed from one form into another.
~Classification of matter.~ At first sight there appears to be no limit to
the varieties of matter of which the world is made. For convenience in
study we may classify all these varieties under three heads, namely,
mechanical mixtures, chemical compounds, and elements.
[Illustration: Fig. 1]
~Mechanical mixtures.~ If equal bulks of common salt and iron filings
are thoroughly mixed together, a product is obtained which, judging by
its appearance, is a new substance. If it is examined more closely,
however, it will be seen to be merely a mixture of the salt and iron,
each of which substances retains its own peculiar properties. The
mixture tastes just like salt; the iron particles can be seen and their
gritty character detected. A magnet rubbed in the mixture draws out the
iron just as if the salt were not there. On the other hand, the salt can be
separated from the iron quite easily. Thus, if several grams of the
mixture are placed in a test tube, and the tube half filled with water and
thoroughly shaken, the salt dissolves in the water. The iron particles
can then be filtered from the liquid by pouring the entire mixture upon
a piece of filter paper folded so as to fit into the interior of a funnel (Fig.
1). The paper retains the solid but allows the clear liquid, known as the
filtrate, to drain through. The iron particles left upon the filter paper
will be found to be identical with the original iron. The salt can be
recovered from the filtrate by evaporation of the water. To accomplish
this the filtrate is poured into a small evaporating dish and gently
heated (Fig. 2) until the water has disappeared, or evaporated. The
solid left in the dish is identical in every way with the original salt.
Both the iron and the salt have thus been recovered in their original
condition. It is evident that no new substance has been formed by
rubbing the salt and iron together. The product is called a mechanical

mixture. Such mixtures are very common in nature, almost all minerals,
sands, and soils being examples of this class of substances. It is at once
apparent that there is no law regulating the composition of a
mechanical mixture, and no two mixtures are likely to have exactly the
same composition. The ingredients of a mechanical mixture can usually
be separated by mechanical means, such as sifting, sorting, magnetic
attraction, or by dissolving one constituent and leaving the other
unchanged.
[Illustration: Fig. 2]
DEFINITION: A mechanical mixture is one in which the constituents
retain their original