Page 17 - 1915, Springs of CA.

NATURAL WATERS. 17

SOURCE AND AMOUNT OF SUBSTANCES IN WATER.
In studying the springs of California certain kinds of mineralized
water were noted as occurring constantly with certain kinds of rocks.
For example, salt springs were noted in areas of marine sediments,
strongly magnesic springs in areas of serpentine, the more noticeably
iron-bearing waters in areas of crystalline rocks containing iron
minerals, and the most siliceous waters in hot springs that rise
through granites or acidic lava rocks. This is mentioned in describ-
ing the individual springs.
The probable sources of some of the constituents of natural waters
are indicated in the following paragraphs:
Silica is present in most waters in relatively small amount, 50
parts per million being an unusually high proportion. It is con-
sidered to exist nearly always as colloidal silica (SiO2), though the
presence of a silicate radicle is indicated by some analyses. Silica is
the chief constituent of the earth's crust and its relative insignifi-
cance in water is accounted for by the fact that it is only slightly
soluble except in strongly alkaline solutions.
Iron and aluminum are widely distributed in nature, though much
less abundant than silica. In most waters iron is present in greater
proportion than aluminum, but the sum of both seldom exceeds 25
parts per million. They are only slightly soluble except in acid
solutions and, as might therefore be expected, are most prominent
in acid waters. A small amount of iron in water may cause rusty
spots on clothes that are washed in it, and the staining of porcelain
plumbing fixtures.
Manganese, barium, and strontium are relatively rare constituents
of rocks and are seldom present in water in weighable amounts.
Calcium and magnesium are normally derived from feldspar and from
magnesian minerals and are among the most abundant and widely
distributed substances in nature. In most waters the proportion of
calcium is two to five times that of magnesium, and where magnesium
is present in relatively large proportion its source is usually evident-
in near-by magnesia-bearing rocks, mainly serpentine. Magnesium
is also likely to exceed calcium in highly concentrated saline waters.
These two substances cause the "hardness" of many waters, and are
the main constituents of the hard scale deposited in cooking utensils
and in steam boilers.
Sodium and potassium are not markedly different from calcium
and magnesium in abundance and distribution in rocks. Their
compounds, with few exceptions, are more soluble than those of
calcium and magnesium, and they are therefore relatively abundant
in the more highly concentrated waters. Both are probably derived
35657° WSP 338 15 2