|T he halved joint is frequently known as half-lapping, and sometimes as checking and half-checking. In the majority of cases it is made by halving the two pieces, i.e., by cutting half the depth of the wood away. There are, however, exceptions ... Read more of The Halved Joint at Wood Workings.ca|| Informational|
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Where Our Drinking Water Comes From
Category: OUR DRINK
Source: A Handbook Of Health
Water Contained in our Food is Pure. Seeing that five-sixths of our
food is water, it is clearly of the greatest importance that that water
should be pure. That part of our water supply which we get in and with
our foods is fortunately, for the most part, almost perfectly pure,
having been specially filtered by the plants or animals which originally
drank it, or having been boiled in the process of cooking.
Water is Always in Motion. The part of our water supply which we take
directly, in the form of drinking water, is, however, unfortunately
anything but free from danger of impurities. The greatest difficulty
with water is that it will not stay put--it is continually on the
move. The same perpetual circulation, with change of form, but without
loss of substance, which is taking place in the engine and in our
bodies, is taking place in the world around us. The water from the
ocean, the lakes, and the rivers is continually evaporating under the
heat of the sun and rising in the form of vapor, or invisible steam,
into the air. There it becomes cooler, and forms the clouds; and when
these are cooled a little more, the vapor changes into drops of water
and pours down as rain, or, if the droplets freeze, as snow or hail. The
rain falls upon the leaves of the trees and the spears of the grass, or
the thirsty plowed ground, soaks down into the soil and seeps or
drains gradually into the streams and rivers, and down these into the
lakes and oceans, to be again pumped up by the sun. All we can do is to
catch what we need of it, on the run, somewhere in the earthy part of
Why our Drinking Water is Likely to be Impure. Every drop of water
that we drink or use, fell somewhere on the surface of the earth, in the
form of rain or snow; and if we wish to find out whether it is pure and
safe, we must trace its course through the soil, or the streams, from
the point where it fell. Our drinking water has literally washed all
outdoors before it reaches us, and what it may have picked up in that
washing makes the possibilities of its danger.
As it falls from the skies, it is perfectly pure--except in large cities
or manufacturing centres, where rain water contains small amounts of
soot, smoke-acids, and dust, but even these are in such small amounts as
to be practically harmless. But the moment it reaches the ground, it
begins to soak up something out of everything that it touches; and here
our dangers begin.
Risks from Leaf Mould. Practically the whole surface of the earth is
covered with some form of vegetation--grass, trees, or other green
plants. These dying down and decaying year after year, form a layer of
vegetable mould such as you can readily scratch up on the surface of the
ground in a forest or old meadow; this is known as leaf mould, or
humus. As the water soaks through this mould, it becomes loaded with
decaying vegetable matter, which it carries with it down into the soil.
Most of this, fortunately, is comparatively harmless to the human
digestion. But some of this vegetable matter, such as we find in the
water from bogs or swamps, or even heavy forests, will sometimes upset
the digestion; hence, the natural dislike that we have for water with a
marshy, or weedy, taste.
Nature's Filter-Bed. When, however, this peaty water soaks on down
through the grass, roots, and leaf mold, into the soil, it comes in
contact with Nature's great filter-bed--the second place in the circuit
where the water is again made perfectly pure. This filter-bed consists
of a layer of more or less spongy, porous soil, or earth, swarming with
millions of tiny vegetable germs known as bacteria. These eagerly pick
out all the decaying vegetable substances of the water and feed upon
them, changing them into harmless carbon dioxid water, and small amounts
of ammonia. Not only will this filter-bed, or spongy mat of bacteria,
burn up and remove all traces of vegetable decay, but if the rain
happens to have soaked through the decaying body of a bird or animal or
insect, the bacteria will just as eagerly feed upon these animal
substances and change them into harmless gases and salts.
By the time the rain water has reached the deeper layers of the soil,
it is again perfectly pure and has also, in seeping through the soil,
picked up certain mineral salts (such as calcium, sodium, and
magnesium) which are of use in the body; so that in an open or thinly
settled country, the water in streams, rivers, and lakes is usually
fairly pure and quite wholesome. That is why, in ancient times, the
great majority of villages and towns and camps were situated on the bank
of some stream, where a supply of water could easily be obtained.
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