Chemistry Reference
In-Depth Information
The pH of solutions is generally measured with a
pH meter
, an instru-
ment that in a single, simple operation measures and yields the pH value
of any water solution, thus making unnecessary any further measurements
or calculations. There are many technically different pH meters, some large,
used mainly in laboratories, others portable, easily taken out for field
measurements. The pH can, however, also be measured using substances
known as
indicators
, which exhibit different colors, shades, or hues at dif-
ferent pH values.
Litmus
, for example, is an indicator that exhibits shades
of red in acid solutions, that is, in solutions having pH values between 7
and 1, and shades of blue when in alkaline solutions with pH values
between 7 and 14.
TABLE 53
pH of Soils and Natural Waters
Matter
pH
Soil
Acid
below 4.5- 6.5
Neutral
6.6- 7.3
Alkaline
7.4- 9.0
Water
Pure
7
Rainwater
5.5- 6
Polluted rainwater
as low as 2.1
Riverwater
7
- 8
Seawater
8
-10
soils to above 10 in strongly alkaline ones. Table 53 lists characteristic pH
values of soils.
Archaeological Soils
The terms
archaeological soils
,
archaeosols
,
anthroposols
, and
paleosols
are vari-
ously used to refer to soils that have been physically and/or chemically altered
by human habitation or activity. The soil of a site constitutes an integral part
of its archaeological record (Wells 2004). It is a well-known fact, for example,
that in areas of intense ancient human habitation the fertility of the soil is
higher than that of the surroundings. Dark soils rich in organic matter often
define, with considerable precision, areas of past intensive human activity.
