Science of Water : Concepts and Applications

100 The Science of Water: Concepts and Applications
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Suspended solids—The quantity of material deposited when a quantity of water, sewage,
or other liquid is fi ltered through a glass fi ber fi lter.
Total solids—The solids in water, sewage, or other liquids; it includes the suspended solids
(largely removable by a fi lter) and fi lterable solids (those which pass through the fi lter).
Saturated solution—The physical state in which a solution will no longer dissolve more of
the dissolving substance—solute.
Colloidal—Any substance in a certain state of fi ne division in which the particles are less
than one micron in diameter.
Turbidity—A condition in water caused by the presence of suspended matter, resulting in
the scattering and absorption of light rays.
Precipitate—A solid substance that can be dissolved, but is separated from the solution
because of a chemical reaction or change in conditions such as pH or temperature.
CHEMISTRY FUNDAMENTALS
Whenever water practitioners add a substance to another substance (from adding sugar to a cup of
tea to adding chlorine to water to make it safe to drink) they perform chemistry. Water operators (as
well as many others) are chemists, because they are working with chemical substances—and how
those substances react is important for them to know and to understand.
MATTER
Going through a day without coming in contact with many kinds of matter would be impossible.
Paper, coffee, gasoline, chlorine, rocks, animals, plants, water, and air—all the materials of which
the world is made—are all different forms or kinds of matter. Previously, matter was defi ned as
anything that has mass (weight) and occupies space—matter is distinguishable from empty space by
its presence. Thus, obviously, the statement about going through a day without coming into contact
with matter is not only correct, but avoiding some form of matter is virtually impossible. Not all
matter is the same, even though we narrowly classify all matter into three groups: solids, liquids,
and gases. These three groups are called the physical states of matter and are distinguishable from
one another by means of two general features, shape and volume.
√ Important Point: Mass is closely related to the concept of weight. On Earth, the weight of
matter is a measure of the force with which it is pulled by gravity toward the Earth’s center.
As we leave Earth’s surface, the gravitational pull decreases, eventually becoming virtually
insignifi cant, while the weight of matter accordingly reduces to zero. Yet, the matter still possesses
the same amount of “mass.” Hence, the mass and weight of matter are proportional to
each other.
√ Important Point: Since matter occupies space, a given form of matter is also associated with
a defi nite volume. Space should not be confused with air, since air is itself a form of matter.
Volume refers to the actual amount of space that a given form of matter occupies.
Solids have a defi nite, rigid shape with their particles closely packed together and sticking
fi rmly to each other. A solid does not change its shape to fi t a container. Put a solid on the ground
and it will keep its shape and volume—it will never spontaneously assume a different shape. Solids
also possess a defi nite volume at a given temperature and pressure.
Liquids maintain a constant volume, but change shape to fi t the shape of their container; they
do not possess a characteristic shape. The particles of the liquid move freely over one another, but
still stick together enough to maintain a constant volume. Consider a glass of water. If we pour
the water into a drinking glass, the water takes the shape of the glass; if we pour it into a bowl,
the water takes the shape of the bowl. Thus, if space is available, any liquid assumes the shape
of the container.