Today is the 200th anniversary of Robert Bunsen, inventor of the famous Bunsen Burner, with which every school lab is equipped with dozens. He is featured in today's Guardian. His reason for wanting a steady hot flame was to study the spectral properties of elements; the characteristic, brightly coloured light emitted by different elements when they are heated. He went on to split this light into its constituent wavelengths using a prism, in the process inventing a prototype of today's spectroscopes and founding the brand new scientific field of spectroscopy. They discovered that every element emits a distinctive mix of wavelengths that can be used like a fingerprint to identify its presence.
The same trick is used by astronomers to examine stars millions of light years away and say exactly what they're made of. Thousands of chemistry students will have sprayed a solution of sodium chloride in a flame to recognise the characteristic orange color. I remember starting out as a pathology doctor measuring sodium and potassium levels using a moving wire flame photometer. Every window in the building had to be closed lest a stray wind blew out the flame.
Bunsen detected a previously unseen blue spectral line produced by mineral water which he guessed was being emitted by an unknown element. Having gone to the extraordinary length of distilling 40 tonnes of water to isolate 17 grams of the new element, he called it caesium, meaning "deep blue" in Latin.
He also discovered that adding iron oxide hydrate to a solution in which arsenic was dissolved would precipitate the poison and render it harmless. To this day, the compound is used as an antidote for arsenic poisoning.
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