100 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, APRIL 1986, VOL. 1 Historical Corner Analytical Spectroscopy: the Beginnings and the Scottish Connection The origins of both atomic absorption and flame emission are to be found in the report produced by Wollastonl in 1802 of dark lines, the Fraunhofer lines, in the prism spectrum of daylight and, in the spectrum of candlelight, the bright yellow lines, later recognised as the Na doublet, and the five distinct coloured bands of the Swan C2 system although their origin was not realised at the time. Wollaston’s report pre-dated Fraunhofer’s more detailed work2 by some 15 years. Fifty years earlier, in 1752, Thomas Melvill, from Glasgow, observed the light emerging from a prism illuminated by a salt-loaded spirit flame through a circular hole in a sheet of pasteboard.He noted that “all sorts of rays were emitted, but not in equal quantities; the yellow being vastly more copious than all the rest put together; and the red more faint than the green and blue. The hole seen through the prism appears uniformly yellow and as distinctly terminated as through a plain glass. . . . Because the hole appears thro’ the prism quite circular and uniform in colour the bright yellow . . . must be of one determined degree of refrangibility and the transition from it to the fainter colour adjoining, not gradual but im- mediate.” The promise of this perceptive work was not realised because of his death the following year at the age of 27 and were it not for this and his unfortunate choice of a circular aperture the discovery of spectral emission lines might have occurred half a century earlier than it did.His lecture was not published until 1756,3 four years after its presentation to a “society in Edinburgh”; contributors to JAAS please note the improved publica- tion times offered now. The later Scottish involvement in flame spectroscopy largely stemmed from the interest in and the work on the properties of light of a remarkable scientist and character, Sir David Brewster, born in Jedburgh in 1781. Licensed as a minister, his extreme nervousness as a preacher induced him to leave the ministry and take up work as a private tutor. He continued his scientific studies, however, and following a series of papers to the Royal Society mainly on the polarisation of light, was elected a Fellow in 1815 and was subsequently awarded the Copley and Rumford medals. He was intimate with most of the scientists of the day including Henry Fox Talbot, then engaged in his early studies on photo- graphy.He was associated with the found- ing of the British Association in 1831 and held the post of Principal of Edinburgh University until his death in 1868. His connection over many years with the Royal Society of Edinburgh as Secretary and finally as President brought many scientists to Edinburgh to report their work. Brewsters contribution in this field included the construction of a monochro- matic lamp based on an alcohol flame,4 which was much used by other investi- gators including Talbot who studied the spectra of the alcohol flame when loaded with a variety of solutions.Talbot,’ dis- cussing the intense homogeneous yellow light then produced, found that “the same effect takes place whether the wick of the lamp is steeped in the muriate (chloride) sulphate or carbonate of soda while the nitrate, chlorate, sulphate and carbonate of potash agree in giving a blueish-white tinge to the flame. Hence the yellow rays may indicate the presence of soda, but they, nevertheless, frequently appear where no soda can be supposed to be present.” Despite his reservations as to the source of the yellow ray, which can be attributed to the failure to realise that the method was so sensitive that trace con- tamination of other solutions with soda was sufficient to produce the yellow ray, his identification of a red ray of a “definite refrangibility and to be characteristic of the salts of potash,” led him to suggest that “whenever the prism shows a homogeneous ray of any colour to exist in a flame this ray indicates the formation orJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, APRIL 1986, VOL.1 101 the presence of a definite chemical com- pound.” These observations and conclu- sions surely take us to the brink of analytical flame spectroscopy. Talbot, referring to the earlier work of Herschel6 who reported the first diagrammatic rep- resentation of salt-loaded alcohol flames, also opines that the “orange ray in the red fire of the theatres may be the effect of the strontia since Mr. Herschel found in the flame of muriate of strontia a ray of that flames containing specific elements and analytical atomic spectroscopy was born. I am indebted to the work of the late R. L. Mitchell8 who drew our attention again to the well-nigh forgotten contribu- tion of Thomas Melvill. References 1. Wollaston, W. H., Phil. Trans., 1802, 92, 365. 2. Fraunhofer, J . , Ann. Physik., 1817, 56, 264. -- .. colour . ” 3. Melvill, T., “Essays and Observations, It was not, however, until 1840 that Physical and Literary,” Volume 2, G . Kirchoff and Bunsen7 showed that Hamilton and J. Balfour, Edinburgh, specific spectral lines were emitted from 1756, p. 12. 4. Brewster, D . , Trans. R. SOC. Edin- burgh, 1823,9,433. 5. Talbot, H. F., Edinburgh 1. Sci., 1826, 5, 77. 6. Herschel, J . F. W . , Trans. R. SOC. Edinburgh, 1823, 9, 445. 7. Kirchoff, G . , and Bunsen, R. W., Ann. Physik., 1860, 110, 161. 8. Mitchell, R. L., in Dean, J . A., and Rains, T. C., Editors, “Flame Emission and Atomic Absorption Spectrometry,’’ Volume 1, Marcel Dekker, New York, 1969, p. 1. Allan M. Ure Macaulay Institute, Aberdeen, UK