Читать книгу Faraday: The Life - James Hamilton - Страница 11

Sir Humphry Davy’s arrival in Paris had been eagerly awaited. For weeks before he came French scientists had been discussing the visit, and making plans for the ceremony at the Institut de France on 2 November 1813 when he was to be awarded the Napoleonic gold medal. Ampère had been especially eager to meet the man he considered ‘the greatest chemist that had ever appeared’,¹ and for his part Ampère was the first person Davy had wanted to meet. Davy was majestically received at the Institut de France, and, seated to the President’s right, was told during the éloge by the Secretary Georges Cuvier that the meeting was ‘honoured by the presence of Le Chevalier Davy’.² He attended receptions and dinners in his honour: at the anniversary dinner of the Philomatic Society both he and Underwood were guests of honour. Toasts were drunk, but as a deference to the two Englishmen all declined to drink Napoleon’s health.³ Despite being a guest in a foreign country, Davy did not curb his opinions of people he met. John Ayrton Paris, his first biographer, reported that it had been observed that ‘during his residence … his likes and dislikes to particular persons were violent, and that they were, apparently, not directed by any principle, but were the effect of a sudden impulse’.⁴ Though Davy expressed dislikes privately, they did not appear in the character sketches of French scientists that he wrote some years later, and which were first published by his brother John: the sketches, of Guyton de Morveau, Vauquelin, Cuvier, Humboldt, Gay-Lussac, Berthollet, La Place and Chaptal, are invariably spirited and appreciative.⁵

On 23 November a deputation of three distinguished French scientists called at the Hôtel des Princes to see Sir Humphry, and set him a problem which not only gave renewed purpose and direction to his months in Paris, but delayed his departure for Italy and held him up in January 1814 in the south of France. André-Marie Ampère, Nicolas Clément and Charles Bernard Desormes were shown into Davy’s drawing room. One of them opened a box and took out a bottle of blackish flakes which had a shiny quality, deep violet in the light, lustrous, not unlike the lights that Davy had seen in Vauquelin’s chromium, though less iridescent. They called it ‘Substance X’. There was not much of a smell to it, and one of the scientists said it was quite brittle in larger lumps. The visitors looked enquiringly at Davy – Faraday was hovering behind trying to see but also trying to be invisible – and Davy looked at the flakes. Then one of the French scientists broke the silence, telling Davy that about two years earlier a gunpowder manufacturer, Bernard Courtois, had produced some crystals when making saltpetre at his works. He had had no idea what the stuff was, but when it was heated it gave off a sharp-smelling, poisonous, lurid violet smoke. The extraordinary thing was that it did not liquefy; it just disappeared on heating in a violet cloud.

There was a great deal of money in gunpowder manufacture in France at that time: there was a war on. Many thousands of barrels had been shipped out to supply the French armies in Spain, Portugal, Russia, Italy and the Austro-Hungarian Empire. Yet more was stockpiled in strategic dumps around France, much of it intended to damage English armies and interests. Gunpowder-making was a very sensitive industry, and the discovery of this strange by-product had to be handled carefully. The nature of the material had stumped even the flamboyant young French chemist Joseph Louis Gay-Lussac. He was a brave and daring figure, popular and famous for undertaking dangerous balloon ascents to gather samples of air for analysis and to take measurements of the strength of terrestrial magnetism. With Alexander von Humboldt he had formulated the law that oxygen and hydrogen combine precisely at the ratio of one to two by volume to make water, and that all gaseous reactions are in such simple proportions. These were revelations of the fundamental driving forces of life, and it was a matter of intense pride for Napoleonic France that a Frenchman was leading the way in analysing them. But even Gay-Lussac could not give a clear answer to what ‘Substance X’ was. He had found that it produced an acid very like hydrochloric acid, and both he and Nicolas Clément had ventured that it was indeed the same acid. And yet …

After two years without reaching any serious conclusion, Ampère seems to have decided that the only thing to do was to ask Sir Humphry Davy. There were clear risks; the dangers of asking a citizen of an enemy country to identify a by-product of gunpowder were obvious. But who else was there to ask? And so the deputation made its way to the Hôtel des Princes.

Sir Humphry asked his visitors how the material was obtained, but they could not or would not tell him. Faraday records: ‘The process by which it is obtained is not as yet publicly known. It is said to be obtained from a very common substance and in considerable quantities.’

Davy took out his travelling box of chemical equipment, and heated a few of the flakes. True to form they vaporised in a dramatic and quite beautiful but poisonous violet smoke. The men choked; someone ran to the window and flung it open. When the smoke had cleared, they took some more of the substance and heated it in a sealed jar. It did not need much heat to start to smoke, and very soon, as it cooled again, it condensed into purple crystals around the neck of the jar. They then dissolved some in alcohol, and formed a deep brown liquid which precipitated silver nitrate. Sir Humphry tipped a bit of this onto a sheet of paper and put it in the sun to dry, where it very quickly tarnished to a dirty black.

Then Sir Humphry tried some other tricks. He leant over his tubes and jars like a magician. He rubbed some of the mystery substance with zinc filings and found that a liquid formed. When it was put into a tube with potassium and heated it flared violently, and the men all backed off. It reacted even more violently when heated with phosphorus, and in combination with mercury a heavy metallic liquid formed which on heating became first orange, then black, then red. Faraday was taking notes of all this, as was his practice, and it is because of these notes, later transcribed into his Journal, that we know so much about this critical scientific meeting. In making the chemical combinations that Faraday described – and in a rented hotel room too – Davy was skimming the edges of extreme physical danger, not only from poisoning by the gas but from the effects of being showered by burning phosphorus or potassium or heated mercury. He was also risking expulsion from the hotel.

Over the next few days Davy made more experiments on the mysterious purple flakes. The visitors probably left him to it, but Faraday was present, as his notes, written out in the Journal under 1 December, make clear. There was much controversy in Paris over whether Davy should have been given a sample to work on alone – Thénard and Gay-Lussac were ‘extremely angry’ with Ampère for giving some to Davy, because Gay-Lussac was intending to publish an analysis of ‘Substance X’.⁶

Davy repeated some of the experiments he had earlier tried in the presence of his visitors: bangs, whooshes, smoke and great stinks issued from the hotel room as he tried combining ‘X’ with iron, zinc, tin, potassium, ammonia. It was all done in tiny quantities, but the results were prodigious: ‘When solution of ammonia is poured on to the new substance and left in contact with it for a short time,’ Faraday recorded, ‘a black powder is formed which when separated, dried and heated, detonates with great force.’⁷

In carrying out all these tests, Davy was rapidly eliminating possibilities for the flaky substance, and approaching a definition. He was racing, in the short time he could spare, to find a solution to the puzzle, and above all to find it before Gay-Lussac or any other Frenchman did. Despite Gay-Lussac’s anger over the freedom Davy had been given to work on ‘Substance X’, Davy had a great respect for his rival. He described him as ‘quick, lively, ingenious, and profound, with great activity of mind, and great facility of manipulation. I should place him at the head of the living chemists of France.’⁸

This was undoubtedly a private battle of wits. Nicolas Clément moved into the fray when he gave a paper at the Institut showing that the substance could be produced by passing sulphuric acid through seaweed ash. But Gay-Lussac was the true rival, not least because Davy had unfinished business with him: three years earlier Gay-Lussac had allegedly suppressed the French publication of a paper on alkalis by Davy.⁹ Perhaps to size up the opposition, Davy and Faraday went to hear Gay-Lussac lecture on vapour to his students at the national school of chemistry in the École Polytechnique. ‘My knowledge of French,’ Faraday wrote later, ‘is so little I could hardly make out the lecture, and without the experiments I should have been entirely at a loss.’

After the lecture they were shown the enormous voltaic battery at the École, comprising six hundred pairs of plates, each seven or eight inches square, which at its best could produce six hundred volts. With some grim chagrin, Faraday noted that the battery had been paid for by the French government, while Davy had had to appeal to the patriotism of the Royal Institution Managers to raise money to buy one for England. He did not ask the government – there was not a hope of government money for scientific equipment in England until Charles Babbage drummed money out of the Exchequer for his Difference Engine in 1823.

Ten days after first being introduced to ‘X’, Davy went to the Jardin des Plantes, where Michel Eugène Chevreul had a laboratory, and the two scientists discussed and worked on the flaky substance together. Faraday was with them, taking notes. By 11 December Davy had concluded that it was an element standing alone, and he coined the name ‘iodine’, from the Greek for ‘violet-like’. On that day he did some final, conclusive tests, trying to pass a current through the material using Chevreul’s voltaic pile. He confirmed that it was an element, individual and apart, an analogue of chlorine, and thought it might come to be used to manufacture pigments, and in gunpowder. That was a fine triumph over French science, although as Faraday put it, with a trace of still lingering caution, ‘as yet it must be considered as a simple body’.¹⁰

With characteristic speed, Davy wrote a paper on iodine, with Faraday’s help as secretary in transcribing his atrocious handwriting and crossings out, which he rushed to the Royal Society in London to be read to his peers.¹¹

While Davy was concluding his tests on iodine, Faraday was already expecting to leave Paris – he had written to his mother on 9 December saying as much.¹² Sir Humphry had received his medal from the Institut, he had met fellow scientists, and he had clinched the iodine question. Nevertheless they stayed on for another three weeks, perhaps so that Davy could discuss iodine further and discover economic natural sources for it, less inherently dangerous than saltpetre. The Monday after Davy had reached his conclusions on iodine, Faraday records that he had at last seen the museum at the Jardin des Plantes; if he was accompanying Davy that day it suggests that Davy’s obsession with finding a source for iodine might have led him to pick over the exhibits in the museum and to discuss them with Cuvier, the Professor of Anatomy at the Jardin des Plantes. It is quite within Davy’s impulsive nature that he should change plans at a moment’s notice, and keep his entourage in uncertainty over what was to happen next. Davy had had many conversations with Cuvier. He had found the Frenchman eloquent in conversation, with ‘a great variety of information on scientific as well as popular subjects … the most distinguished man of talents I have known; but I doubt if he is entitled to the appellation of a man of genius’.¹³

From Davy this was a great compliment. Davy too was loquacious, a formidable conversationalist, and, like Cuvier, he came by the end of his life to extend his thought and philosophy to the widest realms of human society and happiness. Davy, however, merely thought and wrote about social progress; Cuvier, as a politician and courtier as well as natural scientist most famous for his interpretations of fossil remains, actually tried to put it into practice. He became a minister after the restoration of the monarchy under Louis XVIII, and stood up to Charles X when he put an end to the freedom of the press in July 1830. Under King Louis-Philippe Cuvier became Minister of the Interior.

The day after Faraday had seen some fossils at the museum in the Jardin des Plantes, those ‘astonishing organic remains’ of mammoths and other mammals that Cuvier had discovered at Montmartre, he walked across the city up the hill to Montmartre to try to find where they had come from, and with luck perhaps to dig up some more. But try as he might, with hand signals, a smattering of French and perhaps some exasperated English, he could not make the plaster-burners in the quarry understand what it was he wanted to see. It could not have been easy to make an early-nineteenth-century French workman understand by hand signals what a fossil was. As a result, Faraday did not get to the cliff to poke about, but he did take a good look at the geology of the place and, remembering Davy’s teaching, noted that ‘The rock is limestone and selenite and is burned for plaster on the spot … This stone is very imperfectly crystallized and looks more like calcarious sandstone. It is nearly all soluble in acids.’¹⁴

If the day had been clear, he might have been rewarded by an incomparable view of Paris. There in the middle distance, then beyond woods and ramparts, lay the city – a small carpet of white, cream, grey, and threads of dark red. The towers of Nôtre Dame stood out crisply, then as now, beside the florid Tour St Jacques, and the roofs of the Louvre draw a line which divides Paris in two along the river. The Seine, low-lying and kept in its place by embankments, is and was then barely visible from Montmartre. Floating upon the city like tethered hot-air balloons are the gleaming domes of the Institut, Les Invalides and the Pantheon, the only building to break the skyline at Montparnasse. But Faraday noted nothing about the view; what instead caught his eye was the clunking telegraph mounted on a tower nearby, which passed its unending semaphore messages to Paris from Boulogne and Lille. By means of the telegraph, Napoleon’s officials could communicate with each other rapidly. According to Andrew Robertson, who also saw the telegraph at work, it took six minutes for a message to reach Lille from Paris, and for an answer to be received.¹⁵ Faraday describes the telegraph relay, and adds a little drawing for good measure. He points out that ‘They are very different to the English telegraphs, being more perfect and simple.’¹⁶

There, standing on a Paris hillside, was a young citizen of an enemy country, who had already aroused the curiosity of the plaster-burners, sketching the equipment that kept Napoleon’s intelligence flowing around the country. How extraordinary that he was not arrested as a spy.

Wandering in these last few days more widely about Paris, Faraday watched a man touting for custom at a ‘Try your Strength’ machine on the Pont des Arts. He also tumbled to the answer to a problem that had been pestering him for some time – what was the occupation of ‘certain men who carry on their backs something like a high tower finely ornamented and painted and surmounted in general with a flag or vane’, which had a flexible pipe attached to it? The answer was that ‘these men are marchands des everything that is fit to drink’,¹⁷ water- or lemonade-carriers.

Sir Humphry had not yet made it clear to the party when they were to leave Paris. It had been on and off for days, but there must have been some indication that departure was imminent because on 18 December Faraday went to the Prefecture of Police to get a passport for interior travel in France, and on Christmas Eve he was writing: ‘we expect shortly to leave this city, and we have no great reason to regret it. It may perhaps be owing partly to the season and partly to ignorance of the language that I have enjoyed the place so little. The weather has been very bad, very cold, much snow, rain &c have continually kept the streets in a foul plight.’¹⁸

But there was one final fine Parisian extravaganza before they departed: Napoleon and the Empress Marie-Louise were to visit the Senate in full state on 19 December. The weather was cold and wet, but Faraday stuck it out on the terrace of the Tuileries, and eventually the long procession of trumpeters, guards and officers of the court wound into sight. At the end of the procession Faraday caught a glimpse of Napoleon in an opulent carriage surmounted by fourteen footmen, ‘sitting in one corner of his carriage covered and almost hidden from sight by an immense robe of ermine, and his face overshadowed by a tremendous plume of feathers that descended from a velvet hat. The distance was too great to distinguish the features well, but he seemed of a dark countenance and somewhat corpulent’ The Emperor was received by his citizens in complete silence: ‘no acclamations were heard where I stood and no comments’.¹⁹

There were, however, joyful acclamations from some members of Sir Humphry Davy’s party in the morning of 29 December, for, as Faraday writes, ‘this morning we left Paris’.²⁰