An Introduction to Chemical Science | Page 7

In cases where it is not convenient to
measure a liquid or weigh a solid, the estimates above will be near
enough for most experiments herein given. Different solids of the same
bulk of course differ in weight, but for one gram what can be piled on a
one-cent piece may be called a sufficiently close estimate. The distance
between two lines of foolscap is very nearly a centimeter. A cubic
centimeter is seen in Figure 1. Temperatures are recorded in the
centigrade scale.



CHAPTER II
.
WHAT CHEMISTRY IS.

6. Divisibility of Matter.
Experiment 4.--Examine a few crystals of sugar, and crush them with
the fingers. Grind them as fine as convenient, and examine with a lens.
They are still capable of division. Put 3 g. of sugar into a t.t., pour over
it 5 cc. of water, shake well, boil for a minute, holding the t.t. obliquely
in the flame, using for the purpose a pair of wooden nippers (Fig. 3). If
the sugar does not disappear, add more water. When cool, touch a drop
of the liquid to the tongue. Evidently the sugar remains, though in a
state too finely divided to be seen. This is called a solution, the sugar is
said to be soluble in water, and water to be a solvent of sugar.
(Fig 3.)
Now fold a filter paper, as in Figure 4, arrange it in a funnel (Fig. 5),
and pour the solution upon it, catching what passes through, which is
called the filtrate, in another t.t. that rests in a receiver (Fig. 5). After
filtering, notice whether any residue is left on the filter paper. Taste a
drop of the filtrate. Has sugar gone through the filter? If so, what do
you infer of substances in solution passing through a filter? Save half
the filtrate for Experiment 5, and dilute the other half with two or three
times its own volume of water. Shake well, and taste.
(Fig 4.)
(Fig 5.) We might have diluted the sugar solution many times more,
and still the sweet taste would have remained. Thus the small quantity
of sugar would be distributed through the whole mass, and be very
finely divided.
By other experiments a much finer subdivision can be made. A solution
of.00000002 g. of the red coloring matter, fuchsine, in 1 cc. of alcohol
gives a distinct color.
Such experiments would seem to indicate that there is no limit to the
divisibility of matter. But considerations which we cannot discuss here
lead to the belief that such a limit does exist; that there are particles of
sugar, and of all substances, which are incapable of further division
without entirely changing the nature of the substance. To these smallest
particles the name molecules is given.
A mass is any portion of a substance larger than a molecule; it is an
aggregation of molecules.
A molecule is the smallest particle of a substance that can exist alone.
A substance in solution may be in a more finely divided state than

otherwise, but it is not necessarily in its ultimate state of division.
7. A Chemical Change.--Cannot this smallest particle of sugar, the
molecule, be separated into still smaller particles of something else?
May it not be a compound body, and will not some force separate it
into two or more substances? The next experiment will answer the
question.
Experiment 5.--Take the sugar solution saved from Experiment 4, and
add slowly 4 cc.of strong sulphuric acid. Note any change of color, also
the heat of the t.t. Add more acid if needed.
A substance entirely different in color and properties has been formed.
Now either the sugar, the acid, or the water has undergone a chemical
change. It is, in fact, the sugar. But the molecule is the smallest particle
of sugar possible. The acid must have either added something to the
sugar molecules, or subtracted something from them. It was the latter.
Here, then, is a force entirely different from the one which tends to
reduce masses to molecules. The molecule has the same properties as
the mass. Only a physical force was used in dissolving the sugar, and
no heat was liberated. The acid has changed the sugar into a black mass,
in fact into charcoal or carbon, and water; and heat has been produced.
A chemical change has been brought about.
From this we see that molecules are not the ultimate divisions of matter.
The smallest sugar particles are made up of still smaller particles of
other things which do not resemble sugar, as a word is composed of
letters which alone do not resemble the word. But can the charcoal
itself be resolved into other substances, and these into still others, and
so on? Carbon is one of the substances from