748. _What is water?_
Water is a fluid composed of _two_ volumes of _hydrogen_ to _one_
of _oxygen_, or _eight_ parts by weight of _oxygen_ to _one_ of
_hydrogen_. It is nearly colourless and transparent.
749. _Why, if a saucer of water be exposed to the air, will it
gradually disappear?_
Because water is highly expansive, and _rises in thin vapour_, when in
contact with warm and dry air.
[Verse: "Behold there ariseth a little cloud from the sea, of the
bigness of a man's hand. And it came to pass in the meantime, that the
heaven was black with clouds and wind, and there was a great rain."--1
KINGS XVIII.]
750. _Why does steam issue from the spout of a kettle?_
Because the heat of the fire passes into the water, and _drives_ its
atoms apart, making those of them that rise quickly to the surface
_lighter than the air_, upon which they consequently rise.
751. _Why does water become solid when it freezes?_
Because the _latent heat of the water_ passes away from between its
atoms into the air; the atoms, therefore, draw closer together.
752. _Why, if the atoms of water draw closer together when freezing,
does ice expand, and occupy greater space than water?_
Because, _when the atoms of water are congealing_, they do not form a
_compact mass_, but arrange themselves _in groups of crystal points_,
which occupy greater space. Water _contracts_ when freezing until it
sinks to 40 deg., and then it _expands_ as ice is formed.
32 deg. is said to be the _freezing_ point, but it should be
called the _frozen_ point.
753. _Why does water boil?_
Because heat, _entering into the lower portions_ of the water,
_expands_ it; the heated portions are then _specifically lighter_ than
those that are cooler; the hot water therefore _rises upward, and
forces the cooler water down_.
754. _What proportion of the earth's surface is covered with water?_
There are about one hundred and forty seven millions of square miles of
_water_, to forty-nine and a half millions of square miles of _land_.
755. _What is the amount of water pressure?_
The pressure of the sea, at the depth of 1,100 yards, is equal to
15,000 lbs. _to the square inch_.
[Verse: "But the land, whither ye go to possess it, is a land of
hills and valleys, and drinketh water of the rain of heaven."--DEUT.
XI.]
756. _What element is the most abundant in nature?_
_Oxygen_, which forms so large a part of _water_. Of animal substances,
_oxygen_ forms _three-fourths_; of _vegetable substances_ it forms
_four-fifths_; of _mineral substances_ it forms _one-half_; it forms
_eight-ninths_ of the _waters_ and _one-fifth_ of the _atmosphere_; and
aggregating the whole creation, from _one-half to two-thirds_ consists
of _oxygen_.
757. _In what ways does man use oxygen?_
Man _eats_, _drinks_, _breathes_, and _burns_ it, in various
proportions and combinations. It is estimated that _the human race_
consume in those various ways 1,000,000,000 lbs. daily; that the _lower
animals_ consume double that amount; and that, in the varied works of
nature, no less than 8,000,000,000 lbs. of _oxygen_ are used _daily_.
758. _Why does water dissolve various substances?_
Because the _atoms of water_ are very minute; they therefore _permeate
the pores_, or spaces, between the atoms of those bodies, and
_overcoming their attraction for each other_, cause them to separate.
759. _Why does hot water dissolve substances more readily than cold?_
Because the _heat assists to repel the particles_ of the substance
undergoing solution, and _gives the water a freer passage_ between the
atoms.
760. _Why is pump water sometimes hard?_
Because, in passing through the earth, it has become impregnated with
mineral matters, usually the _sulphate_ and _carbonate of lime_.
761. _Why is rain water soft?_
Because it is derived from vapours which, in ascending to the clouds,
_could not bear up the mineral waters with them_. It therefore became
purified or distilled.
762. _Why do kettles become encrusted with stony deposits?_
Because that portion of the water which is driven off in steam _leaves
the mineral matters behind_; they therefore form a crust around the
sides of the kettle.
[Verse: "He gathereth the waters of the sea together as an heap; he
layeth up the depth in storehouses."--PSALM XXXIII.]
It is said that if a child's marble be placed in a kettle, it will
attract the earthy particles, and prevent the encrusting of the
sides of the vessel.
763. _Why is it difficult to wash in hard water?_
Because the soap unites with the mineral matters in the water, and
being _neutralised_ thereby, cannot _dissolve the dirt_ which we desire
to cleanse away.
764. _Why is the sea salt?_
Because salt is a mineral which prevails largely in the earth, and
which, _being very soluble in water_, is taken up by the ocean.
Lakes and rivers, also, even those that are considered fresh, hold in
solution _some degree of saline matters_, which they contribute to the
ocean.
As, in the evaporations from the sea, the salt remains in it, while the
vapours fall as rain, and again wash the earth and carry some of its
mineral properties to the ocean, the _greater saltness of the sea_, as
compared with rivers, is accounted for.
By some persons the opinion is entertained that the sea has been
_gradually getting salter_ ever since the creation of the world. This,
they say, arises from the evaporation of water free from salt, and the
returns of the water to the sea, taking with it salt from the land.
765. _What is the estimated amount of salt in the sea?_
The amount of common salt in the various oceans is estimated at
3,051,342 _cubic geographical miles_, or about five times more than the
mass of the mountains of the Alps.
766. _What is the depth of the sea?_
The extreme depth has not, probably, been ascertained. But Sir James
Ross took soundings about 900 miles west of St. Helena, whence he
found the sea to be nearly _six miles in depth_. Now, if we take the
height of the highest mountain to be five miles, the distance from that
extreme rise of the earth, to the known depth of the sea, will be no
less than _eleven miles_.
767. _Why are the waters of some springs impregnated with mineral
matters?_
Because the water passes through beds of soda, lime, magnesia, carbonic
acid, oxides of iron, sulphate of iron, &c., &c., and _takes up in
some slight degree the particles of those minerals_, according to the
proportions in which they abound.
[Verse: "Who hath measured the waters in the hollow of his hand, and
meted out heaven with the span, and comprehended the dust of the earth
in a measure and weighed the mountains in scales, and the hills in a
balance?"--ISAIAH XL.]
768. _Why does iron rust rapidly when wetted?_
Because the water contains a large proportion of oxygen, some of which
combines with the iron and forms _an oxide of iron_, which is _rust_.
769. _Why does stagnant water become putrid?_
Because the _large amount of oxygen_ which it contains accelerates the
decomposition of dead _animal and vegetable substances_ that accumulate
in it.
770. _Is there danger in drinking water on account of the living
animalcules which it contains?_
No danger arises from the _living creatures_ in water; but
_putrefactive_ matters may produce serious diseases.
771. _What is the best method of guarding against impurities?_
By obtaining water from the purest sources, and by filtering it before
drinking, by which nearly all extraneous matters would be _separated
from it_.