en distilled, contains air,
and it is due to this fact, that aquatic animals can live in it; for
example, put a fish in distilled water and it will soon die.

MINERAL IMPURITIES. Rain-water, which has filtered through the soil and
strata of the earth, dissolves the soluble materials, and carries them
down to lower levels, until they finally collect in the sea. Common
well, spring, and mineral waters contain from 5 to 60 grains to the
gallon; sea-water contains 2,000 grains while in some parts of the Dead
Sea there are 20,000 grams to the gallon. The principal mineral
impurities of well and spring water are lime, magnesia, soda, and oxide
of iron, combined with carbonic and sulphuric acids, forming carbonates,
sulphates, and chloride of sodium, or common salt. The most general,
however, are carbonate and sulphate of lime.

Mineral waters are usually obtained from springs which contain a
considerable amount of saline matter. Those waters which abound in salts
of iron are called _chalybeate_ or _ferruginous_. Those containing salt
are termed _saline_. Those in which contain sulphur are termed
_sulphurous_. Water derives the quality of hardness from the salts of
lime--chiefly the sulphates--which it contains. Hard water, being an
imperfect solvent, is unsuitable for washing purposes. There are two
varieties of hardness, one of which is temporary, being due to the
presence of carbonic acid gas in the water which holds the salts in
solution and may be removed by merely boiling the water and thus
expelling the gas when the salts are deposited, while the other is
permanent and can only be removed by the distillation of the water. It
has been ascertained that twelve pounds of the best hard soap must be
added to 10,000 gallons of water of one degree of hardness before a
lather will remain and, consequently, 0.12 lb. to 100 gallons of water
is a measure of one degree of hardness. Since hard water is not so
useful in cooking and other domestic purposes, as soft water, causing a
great waste of labor and material, it is often highly desirable to
soften it, which is effected by the addition of lime in what is known as
_Clark's process_. One ounce of quicklime should be added to 1000
gallons of water for each degree of hardness. It should be first slacked
and stirred up in a few gallons and then thoroughly mixed with the
entire quantity. Then it should be allowed to remain, and will become
clear in about three hours, but should not be