All springs contain a certain portion of air and gas, and also some
solid matter, usually in the form of salts. When these salts are
abundant, mineral springs are the result, which may be classified
according to the character of their several properties, as acidulous,
chalybeate, sulphurous, saline, calcareous, and silicious.
Acidulous or acid springs are those surcharged with carbonic acid
gas.
Chalybeate springs are those in which iron, in the form of carbonate
or sulphate, is held in solution.
Sulphur, in the form of sulphureted hydrogen or sulphate of lime, is
the distinguishing ingredient in Sulphurous springs.
Saline springs are of two kinds--brine and medicinal; brine when
containing a greater or less amount of chloride of sodium or common
salt, and medicinal when containing other salts, as sulphate of
soda, etc.
Calcareous springs are those highly charged with the salts of lime,
and which have the property of petrifying substances placed within
their reach, and also of depositing their contents, forming the
stalactites and stalagmites of caverns, etc.
Silicious springs are so called from holding silica or flint in
solution. The last-named are all hot or thermal as well as mineral
springs, deriving their heat either from the natural heat of the
earth at great depths, or from volcanic action. When occurring near
volcanoes, they are frequently charged with bitumen, petroleum,
naptha, asphaltum, etc.