Перевод текста.Change in Volume on Change of State1(a) Solid to Liquid.

Перевод текста.
Change in Volume on Change of State1
(a) Solid to Liquid. On solidification
a liquid may either expand
or contract
.
Water expands when it becomes ice, increasing its volume by about 10%. This expansion
accounts for the bursting of pipes
and is of great importance in refrigeration
. In general,
food in cold storage is kept at a temperature just above freezing point
so that the quality
of the food is maintained
and the multiplication of bacteria prevented
. The crumbling of
rocks is largely due to the freezing of water in the fissures which causes further "
splitting. In a similar manner, large lumps of soil are broken into small pieces during
frosty weather.
Most substances, unlike water, contract on solidification. In making a casting, due
allowance has to be made for the contraction of the molten metal on solidification.
Type metal is an exception to this rule, for it is a special alloy which expands on
solidifying, thereby producing a very sharp cast.
The contraction of fats and waxes is shown by the depressed surfaces formed as they
change to the solid state.
A solid which contracts on melting floats in its own liquid, e.g. ice floats on water,
but solids in the other class sink in their own liquids.

(b) Liquid to Vapour. When a liquid boils, it produces vapour
which, at
atmospheric pressure, occupies a volume greater than that of the liquid: e.g. steam at
atmospheric pressure has a volume 1,700 times that of the water from which it is formed.
If a liquid is boiled in an enclosed space, the escaping vapour will create a high
pressure and perhaps burst the enclosing vessel
. We are told that Watt, the inventor of
the steam engine, boiled water in a kettle which had its lid fastened down and a
cork in its spout
. Very soon the cork was shot out with terrific force!
The diagram (Fig. 2) shows the essential parts of a simple steam engine. Steam
from the boiler is passed into the box В fitted on
the side of the cylinder C. In the
cylinder the piston P which is driven first to one end and then to the other by steam
which enters in turn through ports X and Y. This is мейд possible by the slide valve S.
When the valve is in the position shown, steam is passed into the cylinder through Y and,
at the same time, the used steam from the other end of the cylinder passes out through
the exhaust O. The slide valve is moved by an eccentric fitted to the shaft carrying the
flywheel F, hence it works in harmony with the piston.