From France the wedding party moved by stages to Italy, with experiments along the way: collecting crystals from the rim of Vesuvius; analyzing gas from natural vents in the mountains (it turned out to be, Davy found, identical with marsh gas, or methane); and, for the first time, performing a chemical analysis of paint samples from old masterworks (‘mere atoms’, he announced).
In Florence, he experimented with burning a diamond under controlled conditions, with a giant magnifying glass. Despite the demonstration of diamond’s inflammability by Lavoisier, Davy had been reluctant, up to this point, to believe that diamond and charcoal were, in fact, one and the same element. It was rather rare for elements to have a number of quite different physical forms (this was before the discovery of red phosphorus, or the allotropes of sulphur). Davy wondered if these might represent different forms of ‘aggregation’ of the atoms themselves, but it was only much later, with the rise of structural chemistry, that this could be defined (the hardness of diamond, it was then shown, was due to the tetrahedral form of its atomic lattices, the softness and greasiness of graphite due to the packing of its hexagonal lattices in parallel sheets).
Davy returned to London after his honeymoon to one of the grandest practical challenges of his lifetime. The Industrial Revolution, now warming up, was devouring ever huger amounts of coal; coal mines were being dug ever deeper, deep enough now to run into the inflammable and poisonous gases of ‘fire-damp’ (methane) and ‘choke-damp’ (carbon dioxide). A canary carried down in a cage could serve as a warning of the presence of asphyxiating choke-damp; but the first indication of fire-damp was, all too often, a fatal explosion. It was desperately important to design a miner’s lamp that could be carried into the lightless depths of the mines without any danger of igniting pockets of fire-damp.
Davy made a crucial observation – that a flame could not pass through a wire mesh or gauze, as long as this were kept cool.[27] He made many different sorts of lamps incorporating this principle, the simplest and most reliable being an oil lamp in which the only way air could get in or out was through screens of wire mesh. The perfected lamps were tried in 1816 and proved not only safe but also, by the appearance of the flame, reliable indicators of fire-damp.
In a further discovery, Davy found that if a platinum wire was put in an explosive mixture, it would become red-hot and glow. He had discovered the miracle of catalysis: how certain substances, such as the platinum metals, might induce a continuing chemical reaction on their surfaces, without being themselves consumed. Thus, for instance, the platinum loop we kept above the kitchen stove would glow when put in the stream of gas, and, becoming red-hot, ignite it. This principle of catalysis was to become indispensable in thousands of industrial processes.[28]
To an extent that I was only to realize later, Humphry Davy and his discoveries were part of our lives, from the electroplated cutlery to the catalytic gas-lighting loop, to photography (which he had been one of the first to perform, making photographs on leather, thirty years or more before others rediscovered the process), to the dazzling arc lamp used to project films in the local cinema. Aluminium, once costlier than gold (Napoleon III, famously, used to give his guests plates of gold, while he himself dined on aluminium), had become cheap and available only with the use of Davyan electrolysis to extract it. And the thousand and one synthetics all around us, from artificial fertilizers to our gleaming bakelite telephones, were all made possible by the magic of catalysis. But, crucially, it was Davy’s personality that appealed to me – not modest, like Scheele, not systematic, like Lavoisier, but filled with the exuberance and enthusiasm of a boy, with a wonderful adventur-ousness and sometimes dangerous impulsiveness – he was always at the point of going too far – and it was this which captured my imagination above all.
12. Images
Photography had become another passion of mine, and my little lab, already so overfull, often doubled as a darkroom as well. If I try to remember what drew me to photography, I think of the chemicals involved – my hands were often stained with pyrogallol, and seemed to smell of ‘hypo’, sodium hyposulphite, all the while; of the special lights – the deep ruby safelight; the large flashbulbs stuffed with shiny, crinkly, inflammable metal foil (usually magnesium or aluminium, occasionally zirconium). I think of the optics – the tiny, flattened image of the world on a ground-glass screen; the delight of different f-stops, of focusing, of different lenses; of all the intriguing emulsions one could use – it was, above all, the processes of photography that fascinated me.
But there was also, of course, the sense of being able to make a very personal and perhaps fugitive perception objective and permanent, especially as I lacked the ability to draw or paint. This was fanned, even before the war, by family photo albums, especially those which went back before my birth, to the beach scenes and bathing machines of the 1920s, the street scenes of London at the turn of the century, the stiffly posed grandparents and great-aunts and great-uncles of the 1870s. There were also, most precious of all, a couple of daguerreotypes, in special frames, dating from the 1850s; these had a detail, a finish, that seemed much finer, more brilliant, than those of the later paper prints. My mother particularly cherished one of these, a photo of her mother’s mother, Judith Weiskopf, taken in Leipzig in 1853.
Then there was the whole wide world outside the family, the printed photos in books and newspapers, some of which struck me with great vividness, like the dramatic photos of the Crystal Palace on fire (these confirmed – or did they suggest? – my own very early memories of it) and photos of airships majestically floating (and another of a Zeppelin coming down in flames). I loved photos of distant people and places, most of all the photos in the National Geographic magazine, which would arrive, with its yellow-edged cover, each month. The National Geographic, moreover, had pictures in color, and these affected me especially. I had seen hand-tinted photos – Auntie Birdie was adept at such tinting – but I had never seen actual color photos before. An H.G. Wells tale, ‘The Queer Story of Brownlow’s Newspaper’, which I read around this time, describes how Brownlow receives one day, instead of his usual 1931 paper, a newspaper dated 1971. What first arouses Mr. Brownlow’s attention, making him realize that he is confronting something incredible, is the fact that this newspaper has photographs in color – something inconceivable to him, living in the 1930s:
Never in all his life had he seen such colour printing – and the buildings and scenery and costumes in the pictures were strange. Strange and yet credible. They were colour photographs of actuality forty years from now.
27
Davy went on with his investigations of flame, and, a year after the safety lamp, published
28
Enlarging on Davy’s observation of catalysis, Dobereiner found in 1822 that platinum, if finely divided, would not only become white-hot, but would ignite a stream of hydrogen passing over it. On this basis he made a lamp consisting basically of a tightly sealed bottle containing a piece of zinc which could be lowered into sulphuric acid, generating hydrogen. When the stopcock of the bottle was opened, hydrogen gushed out into a small container holding a bit of platinum sponge, and instantly burst into flame (a slightly dangerous flame, because it was virtually invisible, and one had to be cautious to avoid being burned). Within five years, there were twenty thousand Dobereiner lamps in use in Germany and England, so Davy had the satisfaction of seeing catalysis at work, indispensable in thousands of homes.