Hard water is usually water which has
invisible lime in it; there are from ten to fifteen grains and more
of lime in every gallon of limestone water. I leave you to calculate
the enormous weight of lime which must be so carried down to the sea
every year by a single limestone or chalk brook. You can calculate
it, if you like, by ascertaining the weight of lime in each gallon,
and the average quantity of water which comes down the stream in a
day; and when your sum is done, you will be astonished to find it one
not of many pounds, but probably of many tons, of solid lime, which
you never suspected or missed from the hills around. Again, by the
time the rain has sunk through the soil, it is still less pure. It
carries with it not only carbonic acid, but acids produced by
decaying vegetables--by the roots of the grasses and trees which grow
above; and they dissolve the cement of the rock by chemical action,
especially if the cement be lime or iron. You may see this for
yourselves, again and again. You may see how the root of a tree,
penetrating the earth, discolours the soil with which it is in
contact. You may see how the whole rock, just below the soil, has
often changed in colour from the compact rock below, if the soil be
covered with a dense layer of peat or growing vegetables.
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