A Guide To The Scientific Knowledge Of Things Familiar Part 80

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 c.h.i.n.k or crack behind.

Q. _Show the WISDOM of G.o.d 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 c.h.i.n.ks.

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?_