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Almost
all-natural waters contain some carbon dioxide, which
they gain in several ways.
Carbon
dioxide gas (CO2) is present in the air to the extent of
0.03 per cent by volume and 0.05 per cent by weight. As
rain falls through the air, it absorbs some of this gas.
On
reaching the earth the rain water - now slightly acid -
will absorb additional amounts of carbon dioxide if it
flows through decaying vegetation. At the same time the
carbon dioxide becomes carbonic acid.
If
the water now passes through limestone formations, its
carbonic acid content will react with the limestone to
form soluble calcium bicarbonate. In this process the
carbonic acid is partially neutralized.
On
the other hand, if water passes through rock formations,
such as granite, no such reaction occurs. The carbonic
acid is not neutralized. It continues as carbonic acid
until drawn to the surface where it can then cause
corrosion if not neutralized.
If
nature or chemical agents do not neutralize carbonic
acid, it will cause corrosion of both copper and
galvanized plumbing systems. In those parts of the
country where the problem is prevalent it is serious,
for it can lead to serious damaging of plumbing
equipment.
Carbon
dioxide, together with carbonic acid, is primarily a
problem in water containing relatively low
concentrations of minerals. In such water there are not
sufficient alkaline salts to buffer the effect of the
carbonic acid.
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