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Historical profile Blazing a trail Robert Bunsen’s explosive career left an indelible impact – both in advancement of knowledge and the ubiquitous gas burner. Mike Sutton follows in his footsteps CHARLES D. WINTERS/SCIENCE PHOTO LIBRARY PHOTO WINTERS/SCIENCE D. CHARLES 46 | Chemistry World | July 2011 www.chemistryworld.org When Iceland’s Mount Hekla erupted compounds which were both (N≡C–C≡N) – he lost consciousness In short in 1845 there were no airliners for poisonous and inflammable. and was dragged to safety by a it to ground. However, like the ash These were the cacodyl Robert Bunsen is best colleague. His researches showed clouds spewed out of Eyjafjallajökull compounds – a name derived from known as the developer that German charcoal-burning in 2010 and Grímsvötn this year, the the Greek word for ‘stinking’ – of a simple but efficient furnaces wasted almost 50 per cent event aroused considerable scientific and their exact composition was gas burner of their fuel, while a later study interest. The Danish government uncertain until Bunsen tackled them. He was a supreme of British coke-fired furnaces (in commissioned an expedition in 1846 His investigations demonstrated experimentalist and was collaboration with the scientist and which included Robert Bunsen, a that they were all derivatives of called upon to investigate politician Lyon Playfair) indicated German chemist whose experience one parent compound, which we volcanic eruptions, blast a wastage rate of 80 per cent. analysing blast-furnace gases now know as tetramethyldiarsine, furnaces and geysers Ironmasters were reluctant to adopt qualified him for the task. (CH3)2As–As(CH3)2. He made significant Bunsen’s suggestion that recycled Having collected samples inside Bunsen described their impact contributions to exhaust gases might be used as a fuel the still-smouldering crater, he vividly: ‘The cacodyl compounds electrochemistry and supplement, but they eventually lowered thermometers into a appear to exert a specific action on became one of the recognised its advantages. geyser shortly before it was due to the nervous system. It is remarkable fathers of spectroscopy While pursuing this research, expel a massive jet of steam. This that when one is exposed to the He never married and Bunsen greatly improved existing audacity was typical of the man – smell of these compounds the lived a frugal life, devoted techniques of gas analysis, making danger never kept him away from tongue becomes covered with a to teaching and research him an ideal candidate for the 1846 a promising line of research. And black coating, even when no further volcano expedition. Letters to his despite many years of investigating evil effects are noticeable.’5 mother from Iceland give a vivid toxic and explosive substances, he Further evil effects did eventually account of his adventures there: survived into his late 80s. follow. In 1843 a sample of cacodyl ‘The scenery in this far north is full Born in Göttingen on 31 March cyanide exploded in Bunsen’s of desolation but is wonderfully 1811, Robert Wilhelm Eberhard laboratory, permanently blinding beautiful, and I shall never regret Bunsen was the fourth and youngest his right eye and poisoning him so that I have seen it, even though it son of Christian Bunsen, professor severely that his life hung in the cost me the unbelievable privations of philology at Göttingen University. balance. But he returned to the and exertions to which we are In later life, Robert recalled that his bench and successfully completed subjected here.’3 youthful stubbornness had been the investigation. After descending through a severe trial for his parents and clouds of steam and fumes into teachers – only his beloved mother Fumes and volcanoes Hekla’s crater – which had been had been able to keep him in check. An industrial project which occupied in full eruption only three months But there was no doubting his Bunsen intermittently from 1838 previously – Bunsen collected intelligence, and he completed his to 1846 exposed him to further A prolific teacher and hundreds of samples for analysis. doctorate at Göttingen aged 19. After risks. While analysing blast furnace committed experimenter, When he lowered his thermometer pursuing further studies in Paris, exhaust gases – which included Bunsen’s name is familiar down the shaft of a quiescent geyser, Berlin and Vienna, he returned home carbon monoxide and cyanogen to every chemist it revealed that the pressure at lower in 1834 to become a privatdozent (a levels was keeping the water liquid licensed but unsalaried university at a temperature well above its tutor) in chemistry. normal boiling point. From 1836 Bunsen taught at the However, the water at the bottom polytechnic school in Kassel, moving of a geyser is in direct contact with on in 1838 to Marburg University, extremely hot rocks, and sooner where he became a full professor or later it boils, despite the intense in 1842. 10 years later he succeeded pressure. The resulting steam Leopold Gmelin as chair of chemistry pushes the superheated water above at the University of Heidelberg, it up the shaft, causing it to boil and remained there until retiring explosively as the pressure on it falls. in 1889. During more than half a These explosions usually (though century of teaching and research not always) occur at predictable he made valuable contributions to intervals – on one occasion Bunsen’s several areas of chemistry. Many geyser blasted a column of steam of his former students also had 50m into the air moments after he distinguished careers. had retreated from it. Stinking poisons Elemental electricity Bunsen’s first significant research Bunsen also made significant (published in 1834) was on the salts improvements to electrical cells. of arsenious acid. It produced the In 1841 he replaced the Grove cell’s important discovery that freshly platinum cathode with a cheaper precipitated ferric hydroxide was one made from specially processed an effective antidote to arsenic carbon, and used a battery of 44 such poisoning. In 1835–6, he isolated cells to power a brilliant arc light. and analysed several previously To measure its intensity accurately, unknown (and highly toxic) he invented a simple but effective cyanide compounds. And between instrument – the grease-spot 1837 and 1843 he investigated photometer – which was widely a family of organo-arsenic used for many years. LIBRARY PHOTO SCIENCE / BRITAIN GREAT OF INSTITUTION ROYAL www.chemistryworld.org Chemistry World | July 2011 | 47 Historical profile From 1852 Bunsen employed this battery to prepare pure samples of reactive metals – including THINKSTOCK strontium, barium, aluminium, and several rare earths – by electrolysing their molten salts. He then determined their specific heats using a sensitive calorimeter of his own design, which measured volume changes in a mixture of ice and water kept at a constant temperature of 0°C. Having obtained reliable specific heat values, Bunsen was able to estimate the atomic weights of these elements, using the law proposed by French chemists Pierre Dulong and Alexis Petit. This helped his former pupils Lothar Meyer and Dmitri Mendeleev to develop their periodic classification systems for the elements – a process which they both began by arranging the elements in ascending order of atomic weight. Bunsen was also the first to prepare pure magnesium in quantity, and in 1859 he recommended burning it as a light source for photography. Commercial portrait photographers soon took up his suggestion and by the end of the century flash powder was a standard ingredient of photo-journalism. Self-contained and disposable magnesium lights were not available until the 1920s, but Bunsen can be legitimately described as the grandfather of the flash-bulb. However, photographic work formed only a small part of his photochemical investigations during the 1850s. Together with his former student Henry Roscoe, Bunsen made an extended study of the photo-catalysed combination of chlorine with hydrogen – a reaction furnace, he designed a novel gas Bunsen’s experiments on by discovering two new elements, which John Draper had already burner in collaboration with his geysers and volcanoes rubidium and caesium. struggled with in New York. Bunsen technician, Peter Desaga. Other often carried great Other mid-19th century and Roscoe found that the rate of workers, including Aimé Argand personal risk scientists – among them George reaction was proportional to the and Michael Faraday, had already Stokes and Anders Ångström – intensity of illumination, but only experimented with gas burners, but argued that an element’s spectrum after an initial ‘induction period’. Bunsen’s version rapidly became the might yield information about They were unable to explain this standard model. its atomic structure. Their hopes delay, but later studies (by David The burner proved particularly were reasonable, but premature Chapman and others) showed that useful for flame tests. However, in – another half-century passed it was caused by traces of organic 1859 Bunsen’s friend, the physicist before Niels Bohr began relating impurities combining with the Gustav Kirchhoff, alerted him to spectral lines to sub-atomic energy photo-activated chlorine. the possibility of improving this exchanges. Meanwhile, Kirchoff and analytical technique by employing Bunsen abstained from theoretical The burner and spectroscopy a prism. The origins of the speculation on this topic, as they did Bunsen’s best known invention spectroscope can