Page 34 - Curriculum Visions Dynamic Book

Everyday uses of silver
One of the most common objects around the home
is the mirror. Mirrors reflect light rays to form an image.
The earliest form of mirror was a disk of polished bronze. However, although this gave some kind of image, the poor reflecting properties of bronze, and the fact that it tarnishes quickly, were serious drawbacks.
The next improvement, and in common use in the Middle Ages, was to use sheets of glass with metal foil attached to the back. Silver was the preferred metal for this because it is soft and could be beaten into thin sheets, and because it is highly reflective.
However, silver tarnishes over time in polluted air (the surface develops a dark silver sulphide coating). To produce a durable mirror, it was necessary to combine the strength of glass and the reflecting properties of silver by binding
the silver to the glass so that hydrogen sulphide in the polluted air could not tarnish the surface.
In 1835 Justus von Liebig developed a way of depositing silver onto glass. The method, known as silvering, is still in use today.
Making a mirror in a tube
To make a mirror in a test tube, silver nitrate, silver hydroxide and ammonia are mixed together in solution together with a reducing agent, in this case glucose.
The tube is then placed in a bath of hot water. Silver is precipitated onto the warm glass tube.
 A silvered mirror produced on the inside of a test tube.
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