King George II attended one of the most elaborate displays of the age at Green Park in London in 1749, following the signing of the Treaty of Aix-la-Chapelle. Handel wrote a ‘grand overture on warlike instruments’, the piece we now know as his Music for the Royal Fireworks. However, Horace Walpole was disappointed that the display itself was ‘pitiful and ill conducted with no change of coloured fires and shapes…and lighted so slowly that scarce anybody had patience to wait for the finishing’. Even if things had gone to his satisfaction, the green of copper would have been the only colour he would have seen apart from the whites and yellows seen in all incandescent fire.
Charles Dickens’s 1836 Sketches by Boz delights in ‘red, blue, and parti-coloured light’ at one display, while in Pendennis (1848) William Thackeray has the girl Fanny Bolton thrilling to fireworks of ‘azure, and emerald, and vermilion!’ Both descriptions imply an intensity of colour far beyond that achievable at the time, and bear witness more to the ever-wishful imagination of the fireworks spectator. Even when strontium and barium salts became available, the red and green colour they gave was often still feeble owing to the presence of impurities.
The early fireworks displays were abstract affairs, but in Victoria’s reign a fashion developed for pictorial representations in flame, with jingoistic re-enactments of Crimean battles and Indian campaigns being especially popular. When there were fewer glorious victories to report, the trend reverted to displays in which there was less to distract from pure pyrotechnic artistry. However, public enthusiasm for fireworks almost died altogether when the novelty of gaslight led to an alternative fad for adorning major buildings with special illuminations at times of celebration.
These days, firework displays are relayed on television, the europium and zinc of the phosphor screen making a feeble imitation of sodium and barium in the night sky, and there are new fears for the pyrotechnist’s art. Hidden among the bushes in a Cambridgeshire layby, I find an unmarked gate that opens to admit me to the redoubt of the Reverend Ron Lancaster, the managing director of Kimbolton Fireworks, Britain’s last remaining maker of display fireworks. Lancaster grew up in Huddersfield, the historical centre of the British firework industry, and began making his own fireworks there during the Second World War. (These were the days when you could easily buy saltpetre and mix your own gunpowder.) He became a curate and later chaplain at Kimbolton School, where he taught the unusual combination of divinity and chemistry. The summer holidays provided ample opportunity for giving firework displays. In 1964, he built a laboratory to pursue his pyrotechnic experiments and finally set up the company.
For a man devoted to bringing joy as well as salvation into people’s lives, I find the reverend in a gloomy mood. The industry cannot survive much longer, he fears. He rattles through a long list of obstacles: ‘health and safety propaganda, supermarket BOGOFs, Chinese imports, bureaucracy’. One protestor wrote to Lancaster: wasn’t he ashamed that his fireworks were filling the atmosphere with cadmium and mercury? ‘I wrote back: look at the crematoria, and the mercury fillings and the exploding pacemakers, I said.’ I can see he faces problems. Following a spate of ‘stupid’ accidents and vigorous consumer campaigning, fireworks retailers have been subjected to a tightening ratchet of restrictions–the noisiest bangers were outlawed, then fireworks with erratic flight, and other fireworks were muffled or tamed. Yet it is anti-social usage rather than the intrinsic danger of fireworks themselves that has driven the new legislation. Most of all, Lancaster regrets the side-effect of all this, which has been to initiate a trend away from back-garden fireworks towards large municipal events, leading to ‘the control of big displays by people who hate fireworks’.
November the Fifth is no help, either. ‘It’s an awful day.’ Lancaster believes Britain would be happier about fireworks if our annual excuse for letting them off did not fall in this dank month. But a kind of Dunkirk spirit means that we stubbornly tough it out each year without ever really enjoying the spectacle. ‘Our phlegmatic approach has killed it. Go to Spain, and see how fireworks have to be part of every fiesta in every community.’ By email, I poll a selection of friends in the United States, Israel, Russia, Italy, Spain…and indeed receive in reply a barrage of festive occasions when fireworks are let off.
Fortunately, perhaps, the Reverend Lancaster’s passion is not running the business, but pyrotechnic research. I steer the conversation on to the problem of colours. Lancaster’s first breakthrough came when he was offered a supply of titanium turnings from an aircraft machine shop. Although they are tricky to handle–they are very hard, which makes them sensitive to friction and hence liable to trigger an accidental ignition–he found a way to incorporate them safely in fireworks, where they burn to produce beautiful silver sparks. A century before, aluminium and magnesium had been introduced into fireworks to similar effect, but titanium is brighter and, moreover, immune to damp. For a time during the 1960s, its white sparkles became quite a fad.
One of Lancaster’s goals was to create new incandescent colours intermediate between those made by the well-known chemical salts. One target was lime-green (barium and copper burn with more of a sea-green colour). Because he is dealing with dazzling light, the pyrotechnist’s craft is more subtle even than that of the artist mixing paints, combining elements of chemistry, ballistics, optics and perception. In the case of lime-green, simply blending the green of copper or barium and the yellow of sodium was not the answer because each colour requires a different flame temperature. Adding magnalium (an alloy of magnesium and aluminium) enabled Lancaster to produce the component colours under greater control at a higher temperature, but this then required the addition of further chemicals to give them intensity.
The creation of a good orange light is likewise not simply a matter of blending the red of strontium, say, and the yellow of sodium. Lancaster discovered that, for some reason to do with human visual perception, a little green is also necessary to produce the desired effect. His eureka moment came at the local cinema as he watched the lights of the Wurlitzer merging from red to green, momentarily producing the colour he was after.
Blue has proved especially elusive. In Napoleonic France, Claude-Fortuné Ruggieri was the first to make systematic use of metal salts to produce coloured flames. These were used for military signalling as well as for public spectacles. He published many editions of his Elémens de Pyrotechnie through the first half of the nineteenth century, giving recipes for many colour compositions but never a blue. No commonly available metal or salt produces a strong blue emission–a blue demands more energy than is typically released from the electronic transitions of excited atoms that generate light. All sorts of substances were tried in the nineteenth century, from ivory to bismuth to zinc, but the best colour that could be managed was a cold white that only looked blue alongside some yellower light. Thackeray’s ‘azure’ was pure exaggeration. Only later was it learnt that copper salts that naturally burnt with a green flame could be chemically modified to burn blue. Before modern regulations, manufacturers sometimes used the poisonous and unstable copper acetoarsenite, the pigment artists call Paris Green, for this purpose. More recently, it has been found that the effect can be produced by the less noxious expedient of burning copper in the presence of chlorine. For good measure, the pyrotechnist will also often trick the eye by sending the blue up together with some contrasting light to produce the illusion of a deeper hue.
I am given to understand that psychology matters as much as chemistry in creating the perfect fireworks display. Today’s organized shows draw large audiences and consume massive amounts of ordnance. The professionalism is admirable, with each firework set off electronically often to the beat of accompanying music with a precision that would have caused Handel to marvel. But the Reverend Lancaster deplores even this development. ‘The problem is that it all happens too quickly, because it is made to be continuous to fit with the music.’ He makes a more subtle point: ‘What you see, and what you thought you saw, depends v
ery much on your viewpoint and the conditions.’ A massive coordinated public display can still disappoint if the weather or the crowds so determine. All the quick-fire razzmatazz can be poor compensation for the cordoned remoteness from the action, whereas a small-scale spontaneous display–Lancaster recalls standing, drink in hand, with friends on the beach at Aldeburgh after the summer carnival, and letting off a few rockets at intervals over the sea–is more likely to be remembered.
And, as I find when November the Fifth rolls round, mild and dry enough, even a modest pack of fireworks is enough to occasion wonder. The colours, red and green, are scorchingly bright. Occasional white flashes produce a retinal burn against which showers of orange sparks from iron filings appear merely brown and hardly luminous. By some chemical or perceptual hocus pocus, one firework produces a quite deep indigo, more an absence than a presence, a momentary void of light in the sky. A simple catherine wheel my nine-year-old son interprets as a solar eclipse, as its bright disc first gathers pace, forcing the firelight centrifugally out to the rim to form a dazzling corona, before rematerializing as a luminous disc once more as it slows and finally dies. The reverend is right. There is more magic here on this muddy field edge, feeling the rain of gritty soot as each rocket goes up and savouring the sulphur fragrance in the misty air.
Cocktails at the Pale Horse
In The Pale Horse by Agatha Christie, a string of murders is found to be attributable to poisoning by the element thallium. Why did Christie choose such a recherché material when she had free rein of all the poisons known to man? How did she know about it?
Thallium was controversial from its first public appearance at the International Exhibition held at South Kensington in 1862, where it was the bone of contention in a sharp scientific dispute. Inspired by Bunsen and Kirchhoff’s discovery of caesium, a young chemist called William Crookes at the Royal College of Chemistry acquired his own spectroscope–one of few in the land–and in 1861 began to turn it on his experiments. Investigating a particular mineral from the Harz mountains, from which he was hoping to obtain tellurium, he observed an unfamiliar line in the green region of the spectrum. ‘Have you ever noticed a single bright green line, almost exactly as far from Na [sodium, yellow] on one side as Li [lithium, red] is on the other side. If not, I have got a new element,’ he wrote to his collaborator. He had indeed got a new element, which he named thallium, after the Greek for the green shoots of new plants, for the discovery was made in the spring. (If thallium weren’t so scarce and poisonous, it might do for Ron Lancaster’s lime-green.) Crookes began scraping together enough of the element to display at the coming exhibition, hopeful that it might assist in his election to the Royal Society.
Meanwhile, Claude-Auguste Lamy, who was professor of science at the University of Lille in France, also isolated thallium, extracting it from residue lining the lead chambers of a sulphuric acid plant. In June 1862, he arrived in London carrying with him a fourteen-gramme ingot of the new metal, which he unveiled at the exhibition, declaring Crookes’s black powder specimen to be no more than an impure sulphide. Crookes was peeved when the Frenchman was awarded an exhibition prize, and enlisted his friends in the scientific press, who loudly proclaimed him as the first British discoverer of an element since Humphry Davy. Crookes duly obtained redress from the exhibition organizers and the following year gained the Royal Society fellowship he coveted.
In Agatha Christie’s thriller, the shady goings-on that we are first made aware of revolve around an old inn, the Pale Horse, which is occupied by three ‘witches’ who are apparently prepared to arrange murders. A hit list is found. Those already found dead have succumbed to sicknesses displaying symptoms of such variety that it is initially supposed they must all have died of unrelated natural causes. However, Mark Easterbrook, the hero of the tale, has his suspicions aroused when he learns that one of the victims’ hair was falling out. ‘Thallium used to be used for depilation at one time–particularly for children with ringworm. Then it was found to be dangerous,’ he explains. ‘It’s mainly used nowadays for rats, I believe.’ It transpires that the coven is a smokescreen, the witches don’t carry out killings to order, and the murders were perpetrated by the ‘witness’ who first implicated them, by replacing objects in his victims’ homes with substitutes contaminated with thallium.
Christie clearly chose thallium in order to prolong the mystery. It is the sheer diversity of the victims’ symptoms that has the book’s characters and us mystified for 300 pages. How did Christie know about it? She tells us through the person of Easterbrook, who is conveniently asked: ‘What put thallium into your head?’ He replies: ‘I read an article on thallium poisoning when I was in America. A lot of workers died one after the other. Their deaths were put down to astonishingly varied causes. Amongst them, if I remember rightly, were…’ and he goes on to itemize twelve diagnosed causes of death and five symptoms (presumably so that we know Christie has done her homework).
The Pale Horse ‘popularized’ thallium, and is surely one reason why it was at first suspected as the poison used against the former Russian spy Alexander Litvinenko, who was assassinated in London in 2006. (The cause of death turned out to be the even more exotic radioactive polonium, although it is likely that the KGB did use thallium in poisoning another dissident, Nikolai Khokhlov, in 1957.)
In other cases, awareness of the dangers of thallium promoted by Christie’s thriller may have helped to foil real-life killers. Reversing the usual presumption that murder fictions encourage copycat killings, The Agatha Christie Companion gives three instances where, it claims, ‘the symptoms of thallium poisoning…were recognized, and lives saved, because of the quick thinking of individuals who just happened to have read The Pale Horse.’ In one instance, a Latin American woman wrote to the author to say that she had identified the symptoms in a man who was being slowly poisoned by his wife. A year or two later, a nineteen-month-old Qatari girl was brought to the Hammersmith Hospital in London apparently dying of a mysterious disease. The doctors were baffled, but a nurse who had read The Pale Horse suggested treatment for thallium poisoning. The infant had ingested thallium used by her parents as insecticide.
The third and most alarming case occurred at the Hadlands photographic works at Bovingdon in Hertfordshire in 1971. Around seventy people were made ill by what became known as the ‘Bovingdon bug’, and two died. The workers suspected environmental pollution, but tests at the factory revealed nothing. At a meeting, the company doctor ruled out heavy-metal contamination, but one worker, Graham Young, interrupted: ‘Do you not think the symptoms are consistent with thallium poisoning?’ The forensic specialist brought in by Scotland Yard, meanwhile, remembered the symptoms described in The Pale Horse. When the police searched Young’s flat they found large quantities of thallium, and in due course he was found guilty of the murders. After the trial, it emerged that he had been recently released from Broadmoor high-security psychiatric hospital, where he had been imprisoned nine years earlier for attempting to poison most of his family including the cat.
The authors of The Agatha Christie Companion don’t comment on the possibility that murderers too might have read The Pale Horse, although Christie herself, thorough as ever, went out of her way to express the hope that they had not. The population at large, meanwhile, remains happily ignorant of the effects of thallium. What else could explain the decision by the perfumer Jacques Evard to launch a men’s fragrance called Thallium, a product whose implied promise includes baldness and impotence?
The Light of the Sun
The search for the elements has always been an edgy business. It happens at the edges of recognized scientific disciplines and at the edges of respectable enquiry. New elements have been found as by-products of the alchemical quest for gold and the philosopher’s stone. Discoveries have been claimed long before there was tangible evidence of pure new material, from the mere colour of a flame or when some inexplicable residue was left after a standard chemical analysis. More of
ten than you would think, these finds have been shown later to be no more than fancies based on these brief, freakish observations and the vain ambition of the would-be discoverer. You could compile a parallel periodic table of a hundred elements that were named in hope and yet never seen. But the story of one element suggests that forgiveness may be more in order than condemnation for those investigators who found themselves caught in these thickets.
Since the spectroscope had revealed new elements in the flames of humble salt and tobacco ash, it was entirely to be expected that before long somebody should take the hot new tool of chemistry and turn it towards the sun. In 1868, the French astronomer Pierre Janssen travelled to the Bay of Bengal to observe the total solar eclipse that would give science its first opportunity to probe the solar atmosphere. Disembarking at Madras, he was greeted by the British governor of the province and invited to set up his observation station where he wished. He chose the cotton town of Guntur, which lay in the middle of the path of the eclipse and nestled between the sea and the mountains, where mist and cloud were unlikely. It rained for several days leading up to the eclipse, and Janssen began to fear that he might have lugged his gear halfway across the world for nothing. However, according to Janssen’s account, on 18 August, ‘the day of the eclipse, the sun shone at rising, although still in a bed of mist; he soon emerged from it, and at the moment when our telescopes gave us notice of the commencement of the eclipse, he shone out in all his brilliancy’. Then, as the darkness enveloped the waiting observers, Janssen recorded: ‘Two spectra, composed of five or six very bright lines, red, yellow, green, blue, and violet’, arising from two ‘magnificent protuberances’ in the corona on either side of the sun at the moment of total eclipse. To the eye, this light appeared not white like full sunlight, but like ‘the flame of a forge fire’. The spectroscope, however, saw discrete lines of colour separated by regions of black, which made it a simple matter to compare them with the spectral lines produced by known elements that had been confirmed in laboratories. While the red and blue lines matched the light–seen also in the normal solar spectrum–emitted by hot atoms of hydrogen, the yellow line did not. Though close in colour, it did not correspond precisely to the characteristic yellow of sodium either. Janssen concluded that this line must be owing to the presence of an unknown element, though, perhaps foolishly, he was not bold enough to give it a name. A couple of months later, the British astronomer Norman Lockyer observed the sun through the autumnal Cambridge sky and, comparing his findings with those from a discharge tube of hydrogen (the principal solar gas), arrived independently at the very same conclusion. Thinking the element might be present only in the sun and not found on earth, Lockyer named it helium after helios, the Greek for sun.
Periodic Tales Page 18
