All liquids expand more than all solids. The volume of the liquid gets
greater as it is heated. The greater the rise in temperature the more it expands. The actual
change in shape of the liquid depends on the shape of the container that it is
in.
In the experiment with the coloured water in a glass flask if
you watch very carefully you will see the level of the water go down when you
first start heating. This is because the glass gets hot first and so expands and
the volume of the beaker therefore increases. This means that the water level
will drop. Then the water starts getting hotter, it expands more than the glass
and so the water level rises.
One important use of this is in the liquid
in glass thermometer. Mercury is often used in thermometers, but for low temperatures alcohol is
preferred because it freezes at a lower temperature.
In a thermometer the
expansion of the liquid is "magnified" by allowing it to expand up a very narrow tube. A small
increase in volume will change the level in the tube a lot.
(N.B a very narrow tube is called
a capillary tube)