The Early History of Spectroscopy PLATINUM CONTRIBUTES TO ITS DEVELOPMENT By Michael A. Sutton Newcastle upon Tyne Polytechnic For over half a century spectroscopy has been flame spectra of a considerable number of a valuable aid in the analysis of the platinum metals. The list did include platinum, but the metals (I), indeed Johnson Matthey purchased only line Miller attributed to it was the distinc- its first spectrograph in 1920(2). For almost a tive yellow one which coincided with century before that, platinum apparatus had Fraunhofer’s dark solar “D” line. In 1856, played an important part in the development of William Swan showed that this almost omni- spectroscopy itself. It therefore seems ap- present yellow line was due to contamination by propriate that William Hyde Wollaston, who small quantities of sodium. He described his developed the first practical method for work- experimental procedure thus: ing platinum (3), was also the first to publish, “One-tenth of a grain of common salt, carefully in 1802,a description of the distinctive patterns weighed in a balance indicating I/I~of a grain, of bright and dark lines in the prismatic spectra was dissolved in 5000 grains of distilled water. of light from the sun, and from various ter- Two perfectly similar slips of platinum foil were then carefully ignited by the Bunsen lamp, until restrial light sources (4). they nearly ceased to tinge the flame with yellow Wollaston himself did not pursue these observations, but several other scientists did so during the first quarter of the nineteenth cen- tury. Joseph von Fraunhofer mapped the dark lines in the solar spectrum which now bear his name (5). John Herschel and David Brewster independently investigated the spectra of several coloured flames; like Fraunhofer, they had been seeking a reliable source of monochromatic light for optical experiments (6). But it was William Fox Talbot who first suggested, in 1826,that their distinctive line patterns could be used in chemical analysis (7). Talbot’s method was to dip a piece of platinum foil into an alcoholic solution of the salt to be analysed, and insert it into the flame of a spirit lamp. Many subsequent experimenters used platinum for this purpose since it did not con- taminate the flame. Brewster, Talbot and Herschel all continued to experiment and publish, and in 1835 Charles William Allen Miller Wheatstone described some spark spectra to 1817-1870 the British Association (8), but the next major Born in lpswich and educated at King’s College effort came from William Allen Miller, Pro- and at Giessen, Miller collaborated with J. F. Daniel1 on electrochemistry. For nine years he fessor of Chemistry at King’s College London was Treasurer of the Royal Society (9). In 1845 Miller published diagrams of the Courtrn or thr Rn\d Swirh d Chmii.tr\ Platinum Metals Rev., 1988, 32, (l), 28-30 28 light; for to obtain the total absence of yellow light necessary precaution, as the spectra might be is apparently impossible. One of the slips was dip- affected even by the minute quantities of salts ped into the solution of salt, and the other into distilled water, the quantity of the solution of salt dissolved from glass containers. adhering to the slip being considerably less than These ultra-pure samples were ignited in 1/20grain, and both slips were held over the lamp Bunsen’s gas burner, which gave a much hotter until the water had evaporated. They were then flame than the old spirit-lamps; but as in most simultaneously introduced into opposite sides of the flame; when the slip which had been dipped previous experiments, they were supported on into the solution of salt, invariably communicated a platinum wire to avoid contaminating the to a considerable proportion of the flame a bright flame. Whether the wire was dipped into a solu- yellow light, easily distinguishable from that caus- tion of the salt to be analysed, or tipped with a ed by the slip which had been dipped into pure water. It is thus proved that a portion of chloride bead of fused crystals, the relatively short dura- of sodium, weighing less than ~/~,ooo,oooof a tion of the coloured light remained a handicap. grain is able to tinge a flame with bright yellow In I 862 Alexander Mitscherlich described an light . .” (10) . ingenious means of overcoming this difficulty. Further studies of spark spectra were It consisted ofan “L” shaped glass tube, open at published in 1859by V. S. M. Van der Willigen the top so that it could be refilled as necessary who also used platinum to support his samples, and closed at the bottom with a plug made of having found that it contributed no lines of its fine platinum threads twisted around a thicker own (I I); but the vital significance of Swan’s wire, so that a steady supply of the solution was break-through was fully recognised by Robert drawn into the flame by capillary action (13). Bunsen and Gustav Kirchhoff, who succeeded Many further technical refinements were in converting this promising but hitherto developed in the next few years, as other unreliable technique into a systematic method physicists and chemists responded to the of chemical anaysis, which they publicised challenge thrown down by Bunsen and Kir- dramatically by announcing the discovery of a chhoff; new elements were discovered, and new new element in I 860 (12).Caesium was isolated theories of radiation, and of the internal struc- from mineral water by the precipitation of its ture of matter, were debated (14).One of the platino-chloride; with this, as with all Bunsen’s most exciting initiatives was the application of samples for spectrum analysis, purity was en- spectrum analysis to the stars, this had been at- sured by recrystallisation (sometimes up to tempted by Fraunhofer but it was only with the fourteen times) in platinum vessels - a more accurate instruments now available that Some examples of line spectra photographed by Huggins and Miller in the early 1860s: from Sir William Huggins, Philos. Trans., 1862, 152, 888. The top band is the solar spectrum, then is descend- ing order the others are platinum in carbon, platinum in nitrogen, plati- num in chlorine, platinum in carbon dioxide and finally gold in carbon monoxide Platinum Metals Rev., 1988, 32, (1) 29 the project became feasible. In the late 1850s Acknowledgement William Huggins had become The idea for this paper came from the late “. a little dissatisfied with the routine Dr. Leslie B. Hunt, then Editor of Platinum character of ordinary astronomical work, and in a Meruls Review, and I am indebted to him for a vague way sought about in my mind for the number of valuable references and helpful sug- possibility of research upon the heavens in a new direction or by new methods. It was just at this gestions. Without his encouragement it would time, when a vague longing after new methods of never have been completed, and I deeply regret observation for attacking many of the problems of that he did not live to see it in its present form. the heavenly bodies filled my mind, that the news reached me of Kirchhoff s great discovery of the true nature and the chemical constitution of the References sun from his interpretation of the Fraunhofer lines. This news was to me like the coming upon F. E. Beamish and J. C. Van Loon, “Analysis of Noble Metals: Overview and Selected Methods”, a spring of water in a dry and thirsty land.” (15) New York, 1977,pp. 33-76; S. I. Ginzburg et al, Shortly afterwards, Huggins encountered W. “Analytical Chemistry of the Platinum Metals”, Transl. W. Kaner, ed. P. Shelnitz, New York, A. Miller at an evening meeting of the Phar- 1975, PP. 346-370 maceutical Society on the subject of spectrum A. R. Powell, Platinum Metals Rev., 1968, 12, analysis. Being neighbours, they walked home (I),22-28 together, continuing the discussion as they M. E. Weeks and H. M. Leicester, “Discovery of the Elements”, (;Rh Edn.), Easton, Pa., 1968, went; this chance event led to a joint research Ch. 9, pp. 385-431; D. McDonald and L. B. project, and to a series of important papers Hunt, “A History of Platinum and its Allied Metals”, London, Ch. pp. (16). They devised an instrument which com- 1982, 9, 147-177 W.H. Wollaston, Philos. Trans., 1802,92, 378 pared directly the spectrum of light from a J. von Fraunhofer, Denkschr. Kon. Akad. Win. celestial source with that of a flame or spark in Miinchen, 1817,5, 193-228; reprinted in Edin- the laboratory, and with it they began to ex- burgh Philos. J., 1823, 9, 26-40, and in “Harper’s Scientific Memoirs”, no. 2, ed. and plore the chemistry of the sun and the stars. Transl. J. S. Ames, London and New York, 1898 Their publications included diagrams and D. Brewster, Trans. Roy. SOC.Edinburgh, 1822, photographs of the flame and spark spectra of 9, 433-4 many elements. Since the purity of the samples W. H. F. Talbot, Edinburgh J. Sci., 1826, 5, 77-81 was of concern to anyone who might be C. Wheatstone, BA Repor?, 1835, 11-12;Chem. repeating their work, they were careful to cite News, 1861,3, 198-201 their sources: thus Huggins records that “I 9 W. A. Miller, Philos. Mag., 1845,27, 81-91 have procured from Messrs. Johnson and Mat- 10 W. Swan, Trans. Roy. SOC.Edinburgh, 1856,21, 41 1-30 they tellurium, palladium, osmium, rhodium, II V. S. M. Van der Willigen, Ann.