Argon (source code)
= Argon
{title2=$\mathrm{Ar}$, $Z=18$}
{wiki}
The <chemical element> with <atomic number> eighteen. <Argon> is a colourless <noble gas>. It can provide a protective atmosphere around hot, reactive materials, for example in <welding>, where excluding <oxygen> limits <oxidation>. Commercial production separates it by <distillation> of liquid air.<Periodic Table by Royal Society of Chemistry/Argon — Element information, properties and uses>[Periodic Table by Royal Society of Chemistry; Fact box, Uses and Natural abundance: atomic number, group, protective atmosphere and liquid-air distillation]{ref}
Its discovery shows why a small disagreement can matter more than a reassuringly repeatable result. Two preparations can each give consistent measurements while producing different <mixtures>. The <Rayleigh-Ramsay argon density experiment> investigated just such a discrepancy. <Gas density> links the weighing to a mean <molar mass>; a separate <separation process> tests which component accounts for it.
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