CHAPTER XXVI.

ICE.

Q. _What is ICE?_

A. FROZEN WATER. When the air is reduced to 32 degrees of heat, water will no longer remain in a _fluid state_.

Q. _Why is SOLID ICE LIGHTER than WATER?_

A. Because water _expands by freezing_; and as the _bulk is increased_, the _gravity_ must be _less_.

Nine cubic inches of water become ten when frozen.

Q. _Why do EWERS BREAK in a FROSTY NIGHT?_

A. Because the water in them _freezes_; and as the _water is expanded by frost_, it bursts the ewers to make room for its increased volume.

Q. _Why does it not expand UPWARDS (like boiling water), and RUN OVER?_

A. Because the _surface_ is first frozen, and the frozen surface acts as a _plug_, which is more difficult to burst than the earthen ewer itself.

Q. _Why do TILES, STONES, and ROCKS often SPLIT in winter?_

A. Because the moisture (which they imbibed) _freezes_, and by its expansion _splits the solid mass_.

Q. _In winter time, FOOT-MARKS and WHEEL-RUTS are often covered with an icy NET-WORK, through the interstices of which the soil is clearly seen,--WHY does the water freeze in NET-WORK?_

A. The water in these hollows froze first at the _sides_ of the foot-prints: other crystals gradually shot across the water, and would have _covered the whole surface_, had not the earth _absorbed_ the water before it had time to freeze.

Q. _In winter time these FOOT-MARKS and WHEEL-RUTS are sometimes covered with a perfect SHEET of ice, and not an icy net-work,--Why is THIS?_

A. The _air being colder_ and the _earth harder_ (than in the former case), the _entire surface_ of the foot-print is frozen over, before the earth can _draw the water in_.

Q. _Why is not the ice SOLID in these ruts?--WHY is there only a very thin FILM or NET-WORK of ice?_

A. Because the earth _absorbs the water_, and leaves the icy _film behind_.

Q. _Does not water expand by HEAT as well as COLD?_

A. Yes; it expands as soon as it is more than 42 degrees _till it boils_, and then it flies off in steam.

Q. _Why do WATER-PIPES frequently BURST in FROSTY weather?_

A. Because the water in them _freezes_; and as the water _expands by frost_, it bursts the pipes to make room for its increased volume.

Q. _When does WATER begin to EXPAND from cold?_

A. Water (which is wisely ordained by God to be an _exception_ to a very general rule) _contracts_ till it is reduced to 42 degrees, and then it _expands till it freezes_.

(Water freezes at 32°.)

Q. _Why does water expand when it freezes?_

A. Because it is converted into _solid crystals_, which _do not fit close_, like the particles of water.

Q. _Why is the water at the BOTTOM of a river NEVER FROZEN?_

A. Because when water is colder than 42 degrees, it instantly _ascends to the surface_; and (if it freezes) _floats there_ till it is melted.

(When a river is frozen, the water below the surface is never less than 42°.)

Q. _Show the WISDOM of GOD in this wonderful exception to a general law._

A. If ice were _heavier than water_, it would _sink_; and a river would soon become a solid _block of ice_, which could never be dissolved.

Q. _Why does not the cold ICE on the SURFACE of a river CHILL the water BENEATH, and make it freeze?_

A. 1st--Water is a _very bad conductor_, and is heated or chilled by CONVECTION only:

2ndly--If the ice on the surface were to communicate its _coldness_ to the water beneath, the _water beneath_ must communicate its _heat to the ice_, and the ice would instantly _melt_: and

3rdly--The ice on the surface acts as a _shield_ to _prevent the cold air from penetrating the river_ to freeze it below the mere crust.

Q. _Why does WATER FREEZE at the SURFACE first?_

A. Because the surface is in _contact with the air_, and the air _carries away its heat_.

Q. _Why does the coat of ice grow THICKER and THICKER, if the frost CONTINUES?_

A. Because the _heat of the water_ (immediately below the frozen surface) _passes through the pores of the ice_ into the _cold air_.

Q. _Why then are not WHOLE RIVERS FROZEN (layer by layer) till they become solid ice?_

A. Because water is _so slow a conductor_, that our frosts never continue _long enough_ to convert a whole river into a solid mass of ice.

Q. _Why does not RUNNING water freeze so fast as STILL water?_

A. 1st--Because the motion of the current _dissolves the crystals_ as fast as they are formed; and

2ndly--The heat of the _under_ surface is more freely distributed to the _upper_ surface by the _rolling water_.

Q. _When RUNNING water is FROZEN, why is the ICE generally very ROUGH?_

A. Because little flakes of ice are first formed and _carried down the stream_, till they meet some _obstacle_ to _stop_ them; _other_ flakes of ice (_impinging against them_) are arrested in like manner; and the _edges_ of the different flakes _overlapping_ each other, _make the surface rough_.

Q. _Why do SOME parts of a RIVER FREEZE LESS than OTHERS?_

A. Because _springs_ issue from the bottom, and (as they bubble upwards) _thaw the ice_, or make it thin.

Q. _When persons FALL into a RIVER in winter time, why does the WATER feel remarkably WARM?_

A. Because the _frosty air_ is at least 10 or 12 degrees _colder_ than the water.

(The water below the surface is at least 42°; but the air 32°, or even less.)

Q. _Why is SHALLOW water FROZEN QUICKER than DEEP water?_

A. Because (as the _whole volume_ of water must be cooled to 42 degrees before the _surface can be frozen_) it will take a longer time to cool down a _deep_ bed of water than a _shallow_ one.

Q. _Why is SEA-WATER RARELY FROZEN?_

A. 1st--Because the _mass of water is so great_ that it requires a very long time to cool the whole volume down to 42 degrees:

2ndly--The _ebb and flow_ of the sea interfere with the cooling influence of the air: and

3rdly--_Salt_ never freezes till the surface is cooled down at least 25 degrees _below the freezing point_.

Q. _Why do some LAKES RARELY if ever FREEZE?_

A. 1st--Because they are _very deep_:

2ndly--Because their water is supplied by _springs_, which bubble from the bottom.

Q. _Why does the DEPTH of the water RETARD its FREEZING?_

A. As the _whole volume of water_ must be reduced to 42 degrees before the _surface will freeze_, the _deeper_ the water, the _longer_ it will be before the whole volume is thus reduced.

Q. _Why do SPRINGS at the bottom of a lake PREVENT its FREEZING?_

A. Because they keep continually sending forth _fresh water_, which prevents the lake from being reduced to the necessary degree of coldness.

Q. _Why is it COLDER in a THAW than in a FROST?_

A. When frozen water is _thawed_, it absorbs _heat from the air and objects around_ to melt its ice, in consequence of which the cold is greatly increased.

Q. _Why is it WARMER in a FROST than in a THAW?_

A. When water freezes it _gives out its latent heat_, in order that it may be converted into _solid ice_; and as much _heat is liberated_ from the water into the air, we feel warmer.

Q. _Why does SALT DISSOLVE ICE?_

A. Water freezes at 32°, but salt and water will not freeze _till the air is 25° colder_: if, therefore, salt be added to frozen water it becomes _liquid_, unless the thermometer stands below 7°, (which it never does in our island).

Q. _Will any thing do INSTEAD of SALT?_

A. Yes; any _acid_, such as sulphuric, nitric, &c.

Q. _Why are SALT and SNOW mixed together, colder than SNOW?_

A. When _salt_ is mixed with snow, it _dissolves the crystals_ into a fluid; and whenever a solid is converted to a liquid, _heat is absorbed_, and the cold made more intense.

Q. _Why does FROST make the EARTH CRACK?_

A. During the warm weather the earth _absorbed abundance of moisture_, which the winter _freezes_: and (as water _expands_ by frost) the expanding water _thrusts the particles of earth apart from each other_, and leaves a chink or crack behind.

Q. _Show the WISDOM of GOD in this arrangement._

A. These _cracks_ in the earth let in the air, the dew and rain, and many gases favourable to vegetation.

Q. _Why does the EARTH CRUMBLE in SPRING?_

A. In spring the _ice_ of the clods _dissolves_, and the particles of earth (which had been held apart by the expanded ice) are left _unsupported_, and tumble into minute parts (because their _cement is dissolved_).

Q. _Why does MORTAR CRUMBLE away in FROST?_

A. If the mortar was not _dried in the warm weather_, its moisture _freezes_, _expands_, and thrusts the particles of the mortar away from each other; but (as soon as the frost goes) the _water condenses_ and leaves the mortar full of cracks and chinks.

Q. _Why does STUCCO PEEL from a WALL in FROSTY weather?_

A. If the stucco was not _dried in the warm weather_, its moisture _freezes_, _expands_, and thrusts its particles away from the wall; but as soon as the water condenses again by the thaw, the stucco (being unsupported) _falls by its own weight_.

Q. _Why cannot BRICKLAYERS and PLASTERERS work in FROSTY weather?_

A. Because the bricks and plaster would _start from their position_ as soon as the _frost_ came and expanded the mortar.

Q. _Why do BRICKLAYERS COVER their work with STRAW in spring and autumn?_

A. Because straw is a non-conductor, and prevents the mortar of their new work from _freezing_ during the cold nights of spring and autumn.

Q. _Why are WATER-PIPES often covered with STALL-LITTER in winter time?_

A. Because straw (being a non-conductor) prevents the _water of the pipes from freezing_, and the _pipes from bursting_.

Q. _Why are delicate TREES covered with STRAW in WINTER?_

A. Because straw (being a non-conductor) prevents the _sap of the tree_ from being frozen.

Q. _Can WATER be FROZEN in any way BESIDES by frosty weather?_

A. Yes; in very many ways. For example--a bottle of water wrapped in _cotton_, and frequently _wetted with ether_, will soon freeze.

Q. _Why would WATER FREEZE if the bottle were kept constantly wetted with ETHER?_

A. Because _evaporation_ would carry off the heat of the water, and reduce it to _freezing point_.

Q. _Why does ETHER freeze under the RECEIVER of an AIR-pump, when the air is exhausted?_

A. Because _evaporation_ is very greatly increased by the _diminution of atmospheric pressure_; and the ether freezes by evaporation.

FREEZING MIXTURES.

1. If nitre be dissolved in water, the heat of the liquid will be reduced 16 degrees.

2. If 5 oz. of nitre, and 5 of sal-ammoniac (both finely powdered) be dissolved in 19 oz. of water, the heat of the liquid will be reduced 40 degrees.

3. If 3 lbs. of snow be added to 1 lb. of salt, the mixture will fall to 0° (or 32 degrees below freezing point).

The two following are the coldest mixtures yet known:--

1. Mix 3 lbs. of muriate of lime with 1 lb. of snow.

2. Mix 5 lbs. of diluted sulphuric acid with 4 lbs. of snow.

Q. _Why is it more easy to SWIM in the SEA than in a RIVER?_

A. Because the _specific gravity_ of salt water is _greater than that of fresh_, and therefore it _buoys_ up the swimmer better.

Q. _How do cooks ascertain if their BRINE be SALT ENOUGH for pickling?_

A. They put an _egg into their brine_. If the egg _sinks_ the brine is _not strong enough_, if the egg _floats_ it _is_.

Q. _Why will the EGG SINK if the brine be NOT STRONG enough for pickling?_

A. As an egg is _heavier than water_, it will _sink_ if immersed therein; but if as much _salt_ be added as the water can dissolve, the egg will _float_.

Q. _Why will the EGG FLOAT in strong BRINE?_

A. Because the specific gravity of _salt and water_ is greater than that of water _only_.

Q. _Why do persons SINK in water when they are UNSKILFUL SWIMMERS?_

A. 1st--Because (in their floundering about) they _take in water_ at their nose and mouth, which makes them _heavier_:

2ndly--FEAR _contracts the body_; and as the body is compressed by fear into a smaller compass, it becomes _heavier_: and

3rdly--The water and fear _take away the breath_; and when the breath is taken from the body, its _bulk is reduced_, and it becomes _heavier_.

Q. _Why can QUADRUPEDS swim MORE EASILY than MAN?_

A. 1st--Because the _trunk_ of a quadruped is _lighter than water_, and this is the greatest part of them:

2ndly--The _position_ of a beast in water is a _natural_ one.

Q. _Why is it MORE DIFFICULT for a MAN to swim than for a BEAST?_

A. Because the _head and limbs_ of a man (like those of a beast) are _heavier_ than water, and these compose more than _half his body_:

2ndly--The _position_ of a man in water is _unnatural_ to him.

Q. _Why can FAT men SWIM more EASILY than SPARE men?_

A. _Fat is lighter than water_; and the _fatter_ a man is, the more _buoyant_ will he be.

Q. _How are FISHES able to ASCEND to the SURFACE of water?_

A. Fishes have an _air-bladder_ near their abdomen: when this bladder is _filled with air_, the fish increases in size; and (being lighter) ascends through the water to its surface.

Q. _How are fishes able to DIVE in a minute to the BOTTOM of a stream?_

A. They _expel the air_ from their air-bladder; in consequence of which, their _size is diminished_, and they sink instantly.