|28 Jun 2023
In preparation for the opening of our Eric Gordon Mallalieu Library, Head of Chemistry, Gordon Prescott has shared two chemistry experiments for display. The first is an ongoing live experiment from 1929, protecting an iron nail from rusting. The second experiment was to produce a silver mirror in a test tube, which was carried out before the Second World War.
Methods of protecting iron from rusting include creating a barrier from the air: greasing, painting, and tinning (for example of food cans).
Sacrificial protection (magnesium slabs on ships and oil rigs; galvanising with zinc) is also used. This experiment from 1929 illustrates that if water vapour is removed from the air in a sealed tube (in this case by being absorbed by anhydrous calcium chloride), an iron nail will not rust for at least 94 years!
Silver Mirror Test
The silver mirror test has been used to distinguish between aldehydes and ketones, and has been used since the 17th century. The reagent, named after its inventor, the German chemist Bernhard Tollens, is a very mild oxidising agent and is warmed with the test reagent in a hot water bath for a few minutes. Aldehydes are very readily oxidised, and they reduce the [Ag(NH3)2]+ which forms part of the solution to silver metal, Ag, which is often deposited on the test tube wall as a silver mirror. This fine example was produced in a Hymers laboratory some time before the Second World War.
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