Seeing the minerals in the museum incited me to get little bags of ‘mixed minerals’ from a local shop for a few pennies; these would contain little pieces of pyrites, galena, fluorite, cuprite, hematite, gypsum, siderite, malachite, and different forms of quartz, to which Uncle Dave might contribute rarer things, like tiny fragments of scheelite which had broken off his larger piece. Most of my mineral specimens were rather battered, often tiny ones that a real collector would sniff at, but they gave me a feeling of having a sample of nature for myself.
It was from looking at minerals in the Geological Museum and studying their chemical formulas that I learned about their composition. Some were simple and invariable in composition – this was true of cinnabar, a mercury sulphide that always contained the same proportion of mercury and sulphur, no matter where a particular specimen was found. But it was different with many other minerals, including Uncle Dave’s favorite scheelite. While scheelite was ideally pure calcium tungstate, some specimens contained a certain amount of calcium molybdate as well. Pure calcium molybdate, conversely, occurred naturally as the mineral powellite, but some specimens of powellite also contained small amounts of calcium tungstate. One might, in fact, have any intermediate between the two, from a mineral that was 99 percent tungstate and 1 percent molybdate to one that was 99 percent molybdate and 1 percent tungstate. This was because tungsten and molybdenum had atoms, ions, of similar size, so that an ion of one element could replace the other within the mineral’s crystal lattice. But above all, it was because tungsten and molybdenum belonged to the same chemical group or family, and nature treated them, with their similar chemical and physical properties, very much alike. Thus both tungsten and molybdenum tended to form similar compounds with other elements, and both tended to occur naturally as acidic salts that crystallized from solution under similar conditions.
These two elements formed a natural pair, were chemical brothers. This fraternal relationship was even closer with the elements niobium and tantalum, which usually occurred together in the same minerals. And the fraternity approached identical twinship in the elements zirconium and hafnium, which not only invariably occurred together in the same minerals, but were so similar chemically that it took a century to distinguish them – Nature herself could hardly do so.
Wandering through the Geological Museum, I also got a sense of the enormous range, the thousands of different minerals in the earth’s crust, and of the relative abundances of the elements that made them up. Oxygen and silicon were overwhelmingly common – there were more silicate minerals than any others, to say nothing of all the world’s sands. And with the standard rocks of the world – the chalks and feldspars, granites and dolomites – one could see that magnesium, aluminium, calcium, sodium, and potassium must make up nine-tenths or more of the earth’s crust. Iron, too, was common; there seemed to be whole areas of Australia as iron-red as Mars. And I could add little fragments of all these elements, in the form of minerals, to my own collection.
The eighteenth century, Uncle told me, had been a grand time for the discovery and isolation of new metals (not only tungsten, but a dozen others, too), and the greatest challenge to eighteenth-century chemists was how to separate these new metals from their ores. This is how chemistry, real chemistry, got on its feet, investigating countless different minerals, analyzing them, breaking them down, to see what they contained. Real chemical analysis – seeing what minerals would react with, or how they behaved when heated or dissolved – of course required a laboratory, but there were elementary observations one could do almost anywhere. One could weigh a mineral in one’s hand, estimate its density, observe its luster, the color of its streak on a porcelain plate. Hardness varied hugely, and one could easily get a rough approximation – talc and gypsum one could scratch with a fingernail; calcite with a coin; fluorite and apatite with a steel knife; and orthoclase with a steel file. Quartz would scratch glass, and corundum would scratch anything but diamond.
A classical way of determining the relative density or specific gravity of a specimen was to weigh a fragment of mineral twice, in air and in water, to give the ratio of its density to that of water. Another, simpler way, and one which gave me a peculiar pleasure, was to examine the buoyancy of different minerals in liquids of different specific gravity – ’heavy’ liquids had to be used here, for all minerals, except ice, were denser than water. I got a series of heavy liquids: first bromoform, which was almost three times as dense as water, then methylene iodide, which was even denser, and then a saturated solution of two thallium salts called Clerici solution. This had a specific gravity of well over four, and even though it looked like ordinary water, many minerals and even some metals would easily float in it. I loved taking my little bottle of Clerici solution to school, asking people to hold it, and seeing their look of surprise as they experienced its weight, almost five times what they might have expected.
I was on the shy side at school (one school report called me ‘diffident’) and Braefield had added a special timidity, but when I had a natural wonder – whether it was shrapnel from a bomb; or a piece of bismuth with its terraces of prisms resembling a miniature Aztec village; or my little bottle of arm-droppingly dense, sensorily stunning, Clerici solution; or gallium, which melted in the hand (I later got a mold, and made a teaspoon of gallium, which would shrink and melt as one stirred the tea with it) – I lost all my diffidence, and freely approached others, all my fear forgotten.
7. Chemical Recreations
My parents and my brothers had introduced me, even before the war, to some kitchen chemistry: pouring vinegar on a piece of chalk in a tumbler and watching it fizz, then pouring the heavy gas this produced, like an invisible cataract, over a candle flame, putting it out straightaway. Or taking red cabbage, pickled with vinegar, and adding household ammonia to neutralize it. This would lead to an amazing transformation, the juice going through all sorts of colors, from red to various shades of purple, to turquoise and blue, and finally to green.
After the war, with my new interest in minerals and colors, my brother David, who had grown some crystals when he did chemistry at school, showed me how to do this myself. He showed me how to make a supersaturated solution by dissolving a salt like alum or copper sulphate in very hot water and then letting it cool. One needed to hang something – a thread or a bit of metal – in the solution to start the process off. I did this first with a thread of wool in a copper sulphate solution, and in a few hours this produced a beautiful chain of bright blue crystals climbing along the thread.
But if I used an alum solution and a good seed crystal to start it off, I discovered, the crystal would grow evenly, on every face, giving me a single large, perfectly octahedral crystal of alum.
I later commandeered the kitchen table to make a ‘chemical garden’, sowing a syrupy solution of sodium silicate, or water-glass, with differently colored salts of iron and copper and chromium and manganese. This produced not crystals but twisted, plantlike growths in the water-glass, distending, budding, bursting, continually reshaping themselves before my eyes.[7] This sort of growth, David told me, was due to osmosis, the gelatinous silica of the water-glass acting as a ‘semipermeable membrane’, allowing water to be drawn in to the concentrated mineral solution inside it. Such processes, he said, were crucial in living organisms, though they occurred in the earth’s crust as well, and this reminded me of the gigantic nodular, kidneylike masses of hematite I had seen in the museum – the label said this was ‘kidney ore’ (though Marcus had once told me they were the fossilized kidneys of dinosaurs).
7
Thomas Mann provides a lovely description of silica gardens in
I shall never forget the sight. The vessel… was three-quarters full of slightly muddy water – that is, dilute water-glass – and from the sandy bottom there strove upwards a grotesque little landscape of variously coloured growths: a confused vegetation of blue, green, and brown shoots which reminded one of algae, mushrooms, attached polyps, also moss, then mussels, fruit pods, little trees or twigs from trees, here and there of limbs. It was the most remarkable sight I ever saw, and remarkable not so much for its appearance, strange and amazing though that was, as on account of its profoundly melancholy nature. For when Father Leverkuhn asked us what we thought of it and we timidly answered him that they might be plants: ‘No,’ he replied, ‘they are not, they only act that way. But do not think the less of them. Precisely because they do, because they try to as hard as they can, they are worthy of all respect.’