They had tried to make tungsten cannonballs at the beginning of the century, he added, but found the metal too hard to work – though they used it sometimes for the bobs of pendulums. If one wanted to weigh the earth, Uncle Dave suggested, and to use a very dense, compact mass to ‘balance’ against it, one could do no better than to use a huge sphere of tungsten. A ball only two feet across, he calculated, would weigh five thousand pounds.
One of tungsten’s mineral ores, scheelite, Uncle Dave told me, was named after the great Swedish chemist Carl Wilhelm Scheele, who was the first to show that it contained a new element. The ore was so dense that miners called it ‘heavy stone’ or tung sten, the name subsequently given to the element itself. Scheelite was found in beautiful orange crystals that fluoresced bright blue in ultraviolet light. Uncle Dave kept specimens of scheelite and other fluorescent minerals in a special cabinet in his office. The dim light of Farringdon Road on a November evening, it seemed to me, would be transformed when he turned on his Wood’s lamp and the luminous chunks in the cabinet suddenly glowed orange, turquoise, crimson, green.
Though scheelite was the largest source of tungsten, the metal had first been obtained from a different mineral, called wolframite. Indeed, tungsten was sometimes called wolfram, and still retained the chemical symbol W. This thrilled me, because my own middle name was Wolf. Heavy seams of the tungsten ores were often found with tin ore, and the tungsten made it more difficult to isolate the tin. This was why, my uncle continued, they had originally called the metal wolfram – for, like a hungry animal, it ‘stole’ the tin. I liked the name wolfram, its sharp, animal quality, its evocation of a ravening, mystical wolf – and thought of it as a tie between Uncle Tungsten, Uncle Wolfram, and myself, O. Wolf Sacks.
‘Nature offers you copper and silver and gold native, as pure metals’, Uncle would say, ‘and in South America and the Urals, she offers the platinum metals, too.’ He liked to pull out the native metals from his cabinet – twists and spangles of rosy copper; wiry, darkened silver; grains of gold panned by miners in South Africa. ‘Think how it must have been’, he said, ‘seeing metal for the first time – sudden glints of reflected sunlight, sudden shinings in a rock or at the bottom of a stream!’
But most metals occurred in the form of oxides, or ‘earths.’ Earths, he said, were sometimes called calxes, and these ores were known to be insoluble, incombustible, infusible, and to be, as one eighteenth-century chemist wrote, ‘destitute of metallic splendour.’ And yet, it was realized, they were very close to metals and could indeed be converted into metals if heated with charcoal; while pure metals became calxes if heated in air. What actually occurred in these processes, however, was not understood. There can be a deep practical knowledge, Uncle said, long before theory: it was appreciated, in practical terms, how one could smelt ores and make metals, even if there was no correct understanding of what actually went on.
He would conjure up the first smelting of metal, how cavemen might have used rocks containing a copper mineral – green malachite perhaps – to surround a cooking fire and suddenly realized as the wood turned to charcoal that the green rock was bleeding, turning into a red liquid, molten copper.
We know now, he went on, that when one heats the oxides with charcoal, the carbon in the charcoal combines with their oxygen and in this way ‘reduces’ them, leaving the pure metal. Without the ability to reduce metals from their oxides, he would say, we would never have known any metals other than the handful of native ones. There would never have been a bronze age, much less an iron age; there would never have been the fascinating discoveries of the eighteenth century, when a dozen and a half new metals (including tungsten!) were extracted from their ores.
Uncle Dave showed me some pure tungstic oxide obtained from scheelite, the same substance as Scheele and the d’Elhuyars, the discoverers of tungsten, had prepared.[4] I took the bottle from him; it contained a dense yellow powder that was surprisingly heavy, almost as heavy as iron. ‘All we need to do’, he said, ‘is heat it with some carbon in a crucible until it’s red-hot.’ He mixed the yellow oxide and the carbon together, and put the crucible in a corner of the huge furnace. A few minutes later, he withdrew it with long tongs, and as it cooled, I was able to see that an exciting change had occurred. The carbon was all gone, as was most of the yellow powder, and in their place were grains of dully shining grey metal, just as the d’Elhuyars had seen in 1783.
‘There’s another way we could make it’, Uncle said. ‘It’s more spectacular.’ He mixed the tungstic oxide with finely powdered aluminium, and then placed some sugar, some potassium perchlorate, and a little sulphuric acid on top. The sugar and perchlorate and acid took fire at once, and this in turn ignited the aluminium and tungstic oxide, which burned furiously, sending up a shower of brilliant sparks. When the sparks cleared, I saw a white-hot globule of tungsten in the crucible. ‘That is one of the most violent reactions there is’, said Uncle. ‘They call this the thermite process; you can see why. It can generate a temperature of three thousand degrees or more – enough to melt the tungsten. You see I had to use a special crucible lined with magnesia, to withstand the temperature. It’s a tricky business, things can explode if you’re not careful – and in the war, of course, they used this process to make incendiary bombs. But if conditions are right, it’s a wonderful method, and it has been used to obtain all the difficult metals – chromium, molybdenum, tungsten, titanium, zirconium, vanadium, niobium, tantalum.’
We scraped out the tungsten grains, washed them carefully with distilled water, examined them with a magnifying glass, and weighed them. He pulled out a tiny, 0.5-milliliter graduated cylinder, filled it to the 0.4-milliliter mark with water, then tipped in the tungsten grains. The water rose a twentieth of a milliliter. I jotted down the exact figures, and worked them out – the tungsten weighed a little less than a gram, and had a density of 19. ‘That’s very good’, Uncle said, ‘that’s pretty much what the d’Elhuyars got when they first made it back in the 1780s.
‘Now I’ve got several different metals here, all in little grains. Why don’t you get some practice weighing these, measuring their volume, working out their density?’ I spent the next hour delightedly doing this and found that Uncle had indeed given me a huge range, from one silvery metal, a little tarnished, which had a density of less than 2, to one of his osmiridium grains (I recognized it), which was almost a dozen times as dense. When I measured the density of a little yellow grain, it was exactly the same as that of tungsten – 19.3, to be exact. ‘You see’, said Uncle, ‘gold’s density is almost the same as tungsten’s, but silver is much lighter. It is easy to feel the difference between pure gold and gilded silver – but you would have a problem with gold-plated tungsten.’
Scheele was one of Uncle Dave’s great heroes. Not only had he discovered tungstic acid and molybdic acid (from which the new element molybdenum was made), but hydrofluoric acid, hydrogen sulfide, arsine, and prussic acid, and a dozen organic acids, too. All this, Uncle Dave said, he did by himself, with no assistants, no funds, no university position or salary, but working alone, trying to make ends meet as an apothecary in a small provincial Swedish town. He had discovered oxygen, not by a fluke, but by making it in several different ways; he had discovered chlorine; and he had pointed the way to the discovery of manganese, of barium, of a dozen other things.
4
The d’Elhuyar brothers, Juan Jose and Fausto, were members of the Basque Society of Friends for Their Country, a society devoted to the cultivation of arts and sciences that would meet every evening, discussing mathematics on Monday evenings, experimenting with electrical machines and air pumps on Tuesday evenings, and so on. In 1777 the brothers were sent abroad, one to study mineralogy, the other metallurgy. Their travels took them all over Europe, and one of them, Juan Jose, visited Scheele in 1782.
After they returned to Spain, the brothers explored the heavy black mineral wolframite and obtained from it a dense yellow powder (‘wolframic acid’) which they realized to be identical to the tungstic acid Scheele had obtained from the mineral ‘tung-sten’ in Sweden, and which, he was convinced, contained a new element. They went ahead, as Scheele had not, to heat this with charcoal, and obtained the pure new metallic element (which they named wolframium) in 1783.