![]() Not only did they realise that the pattern of lines in the spectrum provided a unique fingerprint for a particular element, but that a novel spectrum would indicate the presence of a previously unreported element: However, it was Bunsen and Kirchhoff who took the next step, recognising its wider application to the chemical analysis of the elements. Source: © Sheila Terry/Science Photo Libraryįlame emission spectra of the alkali metals Alter showed that the spectrum derived from brass was indeed made up from the spectra of its two components: zinc and copper. Following on from this work, William Allen Miller, professor of chemistry at King's College London, and David Alter, an American physician and inventor, published in 18, respectively, the emission spectra of various elements. Talbot later differentiated between lithium and strontium compounds using this method: both give red-coloured flames, but their spectra are quite different. Pioneer British photographer William Fox Talbot took this work further and in 1826 reported:Ī glance at the prismatic spectrum of a flame may show it to contain substances which it would otherwise require a laborious chemical analysis to detect. Nearly 30 years before, in 1822, John Herschel had passed light from various coloured flames through a prism and noticed patterns of bright, coloured lines separated by regions of darkness, but made little of it. Kirchhoff's suggestion was crucial, but scarcely novel. 3 This would separate yellow sodium light from the more distant violet colour of potassium. Kirchhoff suggested to Bunsen that he could improve on this by passing the light through a prism. A deep blue 'cobalt' glass filter transmits the violet hue of potassium but blocks the yellow of sodium (which is a common impurity in potassium salts). Melvill's observations languished for 70 years before prisms were again used to analyse light emitted by coloured flames, and it was a century before Bunsen tried to develop a method of analysis from this phenomenon.Īware that the intensity of some colours, such as those from sodium compounds, could mask less intense colours of other elements, Bunsen used filters to cut out some colours. Sodium compounds 'burnt' with a yellow flame while potassium salts produced violet flames. Five years later, chemist Andreas Sigismund Marggraf reported that he could distinguish between sodium and potassium compounds by their different coloured flames. Sadly, Melvill died in 1753, aged only 27. Gustav Kirchhoff (left) and Robert Bunsen (right)
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