ually called
_hardness_, and which is always owing to salts with an earthy base.

If we wish to know the nature of the different acids and earths
contained in the water, the following test may be employed.[15]

EXPERIMENT.

Add about twenty drops of a solution of oxalate of ammonia, to half a
wine-glass of the water; if a white precipitate ensues, we conclude that
the water contains lime.

By means of this test, one grain of lime may be detected in 24,250 of
water.

If this test occasion a white precipitate in water taken fresh from the
pump or spring, and not after the water has been boiled and suffered to
grow cold, the lime is dissolved in the water by an excess of carbonic
acid; and if it continues to produce a precipitate in the water which
has been concentrated by boiling, we then are sure that the lime is
combined with a fixed acid.

EXPERIMENT.

To detect the presence of iron, add to a wine-glassful of the water a
few drops of an infusion of nut-galls; or better, suffer a nut-gall to
be suspended in it for twenty-four hours, which will cause the water to
acquire a blueish black colour, if iron be present.

EXPERIMENT.

Add a few grains of muriate of barytes, to half a wine-glass of the
water to be examined; if it produces a turbidness which does not
disappear by the admixture of a few drops of muriatic acid, the presence
of sulphuric acid is rendered obvious.

EXPERIMENT.

If a few drops of a solution of nitrate of silver occasions a milkiness
with the water, which vanishes again by the copious addition of liquid
ammonia, we have reason to believe that the water contains a salt, one
of the constituent parts of which is muriatic acid.

EXPERIMENT.

If lime water or barytic water occasions a precipitate which again
vanishes by the admixture of muriatic acid, then carbonic acid is
present in the water.

EXPERIMENT.

If a solution of phosphate of soda produces a milkiness with the water,
after a previous addition to it of a similar quantity of neutral
carbonate of ammonia, we may then expect magnesia. The application of
this test is best made in the following manner:

Concentrate a quantity of the water to be examined to about 1/20 part of
its bulk, and drop into about half a wine-glassful, about five grains of
neutral carbonate of ammonia. No magnesia becomes yet precipitated if
this earth be present; but on adding a like quantity of phosphate of
soda, the magnesia falls down, as