Page 5 - Curriculum Visions Dynamic Book

discovered a wide range of alloys in which zinc can play a vital role. About one-tenth of all zinc is now used for making the cases of dry cells (dry batteries).
Mercury
Mercury, symbol Hg, is the only metal that is a liquid at room temperature. It is one of the rarest metals, and yet it is found in many homes – in the form of the silvery liquid in thermometers.
Mercury is named after the planet and has been recognised since ancient times. This is perhaps because the bright red ore of mercury, called cinnabar, was attractive to ancient civilisations as a pigment for paint. Ancient civilisations also discovered that by simply heating the cinnabar, liquid mercury flows out.
The Greeks named the element hydrargyros, after its “quicksilver” properties. This is why the chemical symbol for mercury is Hg.
Cadmium
Cadmium, symbol Cd, gets its name from the old term
for zinc ore, cadmia, because it was first discovered with zinc ore. Like zinc, cadmium is a reactive metal that
readily plates onto other metals. Its special advantage
is that cadmium has a very low friction, making it ideal
for use on ball bearings and other moving parts. But it
is in batteries and in photoelectric cells that cadmium becomes part of everyday life. Every time street lights come on automatically at dusk, or we rely on the automatic exposure meter of a camera, we are making use of photosensitive cells made with cadmium compounds.
 A piece of zinc reacting with dilute hydrochloric acid results in bubbles of hydrogen gas.
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