In the passage, it is pointed out that mercury _____ .

Mercury has a number of interesting properties and a
variety of industrial uses. It expands at a constant rate
through the range of temperatures at which it is a
liquid. Because of this property and because it does
not cling to glass, mercury is often used in
thermometers. At ordinary temperatures it evaporates
very slowly and can thus be left in an open container
for long periods of time. For this reason it is used in
one type of barometer. Mercury is a good electrical
conductor and is used in sealed electrical switches.
An electric current passing through mercury vapour
causes it to give off light, hence its use in certain
kinds of lamps.