Environmental Engineering Reference
In-Depth Information
Table 2.1 WaTer ProPerTies
specific
Weight
(lb/ft
3
)
specific
Weight
(lb/ft
3
)
Temperature
(°f)
density
(slugs/ft
3
)
Temperature
(°f)
density
(slugs/ft
3
)
32
62.4
1.94
130
61.5
1.91
40
62.4
1.94
140
61.4
1.91
50
62.4
1.94
150
61.2
1.90
60
62.4
1.94
160
61.0
1.90
70
62.3
1.94
170
60.8
1.89
80
62.2
1.93
180
60.6
1.88
90
62.1
1.93
190
60.4
1.88
100
62.0
1.93
200
60.1
1.87
110
61.9
1.92
210
59.8
1.86
120
61.7
1.92
Suppose you had a tub of lard and a large box of cold cereal, each
having a mass of 600 g. The density of the cereal would be much less
than the density of the lard because the cereal occupies a much larger
volume than the lard occupies. The density of an object can be calcu-
lated by using the formula:
Mass
Volume
Density
=
(2.2)
In water/wastewater treatment, perhaps the most common mea-
sures of density are pounds per cubic foot (lb/ft
3
) and pounds per gallon
(lb/gal):
•
3
of water weighs 62.4 lb; density = 62.4 lb/ft
3
1 ft
•
1 gal of water weighs 8.34 lb; density
= 8.34 lb/gal
The density of a dry material, such as cereal, lime, soda, or sand,
is usually expressed in pounds per cubic foot. The density of a liquid,
such as liquid alum, liquid chlorine, or water, can be expressed either as
pounds per cubic foot or as pounds per gallon. The density of a gas, such
as chlorine gas, methane, carbon dioxide, or air, is usually expressed in
pounds per cubic foot.
As shown in Table 2.1, the density of a substance such as water
changes slightly as the temperature of the substance changes. This
occurs because substances usually increase in volume (size) by expand-
ing as they become warmer. Because of this expansion with warming,
the same weight is spread over a larger volume, so the density is lower
when a substance is warm than when it is cold.
Note:
What is specific gravity? Specific gravity is the weight (or density)
of a substance compared to the weight (or density) of an equal volume of
water. The specific gravity of water is 1.
