Making of the Atomic Bomb

by Richard Rhodes

  Then Bohr arrived and the question they discussed was Bohr’s old insight that the order of the elements in the periodic table ought to follow the atomic number rather than, as chemists thought, the atomic weight. (The atomic number of uranium, for example, is 92; the atomic weight of the commonest isotope of uranium is 238; a rarer isotope of uranium has an atomic weight of 235 and the same atomic number.) Harry could look for regular shifts in the wavelengths of X-ray line spectra and prove Bohr’s contention. Atomic number would make a place in the periodic table for all the variant physical forms that had been discovered and that would soon be named isotopes; atomic number, emphasizing the charge on the nucleus as the determiner of the number of electrons and hence of the chemistry, would strongly confirm Rutherford’s nuclear model of the atom; the X-ray spectral lines would further document Bohr’s quantized electron orbits. The work would be Moseley’s alone; Darwin by then had withdrawn to pursue other interests.

  Bohr and the patient Margrethe went on to Cambridge to vacation and polish Bohr’s paper. Rutherford left near the end of July with Mary on an expedition to the idyllic mountains of the Tyrol. Moseley stayed in “unbearably hot and stuffy” Manchester, blowing glass. “Even now near midnight,” he wrote his mother two days after Rutherford’s departure, “I discard coat and waistcoat and work with windows and door open to try to get some air. I will come to you as soon as I can get my apparatus to work before ever I start measurements.”307 On August 13 he was still at it. He wrote his married sister Margery to explain what he was after:

  I want in this way to find the wave-lengths of the X ray spectra of as many elements as possible, as I believe they will prove much more important and fundamental than the ordinary light spectra. The method of finding the wavelengths is to reflect the X rays which come from a target of the element investigated [when such a target is bombarded with cathode rays]. . . . I have then merely to find at which angles the rays are reflected, and that gives the wavelengths. I aim at an accuracy of at least one in a thousand.308

  The Bohrs returned to Copenhagen, the Rutherfords from the Tyrol, and now it was September and time for the annual meeting of the British Association, this year in Birmingham. Bohr had not planned to attend, especially after lingering overlong in Cambridge, but Rutherford thought he should: his quantized atom with its stunning spectral predictions would be the talk of the conference. Bohr relented and rushed over. Birmingham’s hotels were booked tight. He slept the first night on a billiard table.309 Then the resourceful de Hevesy found him a berth in a girls’ college. “And that was very, very practical and wonderful,” Bohr remembered afterward, adding quickly that “the girls were away.”310

  Sir Oliver Lodge, president of the British Association, mentioned Bohr’s work in his opening address. Rutherford touted it in meetings. James Jeans, the Cambridge mathematical physicist, allowed wittily that “the only justification at present put forward for these assumptions is the very weighty one of success.”311 A Cavendish physicist, Francis W. Aston, announced that he had succeeded in separating two different weights of neon by tediously diffusing a large sample over and over again several thousand times through pipe clay—“a definite proof,” de Hevesy noted, “that elements of different atomic weight can have the same chemical properties.”312 Marie Curie came across from France, “shy,” says A. S. Eve, “retiring, self-possessed and noble.”313 She fended off the bulldog British press by praising Rutherford: “great developments,” she predicted, were “likely to transpire” from his work. He was “the one man living who promises to confer some inestimable boon on mankind.”314

  Harald Bohr reported to his brother that autumn that the younger men at Gottingen “do not dare to believe that [your paper] can be objectively right; they find the assumptions too ‘bold’ and ‘fantastic.’ ”315 Against the continuing skepticism of many European physicists Bohr heard from de Hevesy that Einstein himself, encountered at a conference in Vienna, had been deeply impressed. De Hevesy passed along a similar tale to Rutherford:

  Speaking with Einstein on different topics we came to speak on Bohr’s theory, he told me that he had once similar ideas but he did not dare to publish them. “Should Bohr’s theory be right, it is of the greatest importance.” When I told him about the [recent discovery of spectral lines where Bohr’s theory had predicted they should appear] the big eyes of Einstein looked still bigger and he told me “Then it is one of the greatest discoveries.”316

  I felt very happy hearing Einstein saying so.

  So did Bohr.

  Moseley labored on. He had trouble at first making sharp photographs of his X-ray spectra, but once he got the hang of it the results were outstanding. The important spectral lines shifted with absolute regularity as he went up the periodic table, one step at a time. He devised a little staircase of strips of film by matching up the lines. He wrote to Bohr on November 16: “During the last fortnight or so I have been getting results which will interest you. . . . So far I have dealt with the K [spectral line] series from Calcium to Zinc. . . . The results are exceedingly simple and largely what you would expect. . . . K = N − 1, very exactly, N being the atomic number.” He had calcium at 20, scandium at 21, titanium at 22, vanadium at 23, chromium at 24 and so on up to zinc at 30. He concludes that his results “lend great weight to the general principles which you use, and I am delighted that this is so, as your theory is having a splendid effect on Physics.”317 Harry Moseley’s crisp work gave experimental confirmation of the Bohr-Rutherford atom that was far more solidly acceptable than Marsden’s and Geiger’s alpha-scattering experiments. “Because you see,” Bohr said in his last interview, “actually the Rutherford work was not taken seriously. We cannot understand today, but it was not taken seriously at all. . . . The great change came from Moseley.”318

  * * *

  Otto Hahn was called upon once more to demonstrate his radioactive preparations. In the early spring of 1914 the Bayer Dye Works at Leverkusen, near Cologne in the Rhineland, gave a reception to celebrate the opening of a large lecture hall.319 Germany’s chemical industry led the world and Bayer was the largest chemical company in Germany, with more than ten thousand employees. It manufactured some two thousand different dyestuffs, large tonnages of inorganic chemicals, a range of pharmaceuticals. The firm’s managing director, Carl Duisberg, a chemist who preferred industrial management along American lines, had invited the Oberpräsident of the Rhineland to attend the reception; he then invited Hahn to add a glow to the proceedings.

  Hahn lectured to the dignitaries on radioactivity. Near the beginning of the lecture he wrote Duisberg’s name on a sealed photographic plate with a small glass tube filled with strong mesothorium. Technicians developed the plate while he spoke; at the end Hahn projected the radiographic signature onto a screen to appreciative applause.

  The high point of the celebration at the vast 900-acre chemical complex came in the evening. “In the evening there was a banquet,” Hahn remembered with nostalgia; “everything was exquisite. On each of the little tables there was a beautiful orchid, brought from Holland by air.” Orchids delivered by swift biplane might be adequate symbols of German prosperity and power in 1914, but the managing director wanted to demonstrate German technological superiority as well, and found exotic statement: “At many of the tables,” says Hahn, evoking an unrecognizably futuristic past, “the wine was cooled by means of liquid air in thermos vessels.”320

  * * *

  When war broke out Niels and Harald Bohr were hiking in the Austrian Alps, covering as much as twenty-two miles a day. “It is impossible to describe how amazing and wonderful it is,” Niels had written to Margrethe along the way, “when the fog on the mountains suddenly comes driving down from all the peaks, initially as quite small clouds, finally to fill the whole valley.”321 The brothers had planned to return home August 6; the war suddenly came driving down like the mountain fog and they rushed across Germany before the frontiers closed. In October Bohr would sail with his wife from neu
tral Denmark to teach for two years at Manchester. Rutherford, his boys off to war work, needed help.

  Harry Moseley was in Australia with his mother at the beginning of August, attending the 1914 British Association meeting, in his spare time searching out the duck-billed platypus and picturesque silver mines. The patriotism of the Australians, who immediately began mobilizing, triggered his own Etonian spirit of loyalty to King and country. He sailed for England as soon as he could book passage. By late October he had gingered up a reluctant recruiting officer to arrange his commission as a lieutenant in the Royal Engineers ahead of the waiting list.

  * * *

  Chaim Weizmann, the tall, sturdy, Russian-born Jewish biochemist who was Ernest Rutherford’s good friend at Manchester, was a passionate Zionist at a time when many, including many influential British Jews, believed Zionism to be at least visionary and naive if not wrongheaded, fanatic, even a menace. But if Weizmann was a Zionist he was also deeply admiring of British democracy, and one of his first acts after the beginning of the war was to cut himself off from the international Zionist organization because it proposed to remain neutral. Its European leaders hated Czarist Russia, England’s ally, and so did Weizmann, but unlike them he did not believe that Germany in cultural and technological superiority would win the war. He believed that the Western democracies would emerge victorious and that Jewish destiny lay with them.

  He, his wife and his young son had been en route to a holiday in Switzerland at the outbreak of the war. They worked their way back to Paris, where he visited the elderly Baron Edmond de Rothschild, financial mainstay of the pioneering Jewish agricultural settlements in Palestine. To Weizmann’s astonishment Rothschild shared his optimism about the eventual outcome of the war and its possibilities for Jewry. Though Weizmann had no official position in the Zionist movement, Rothschild urged him to seek out and talk to British leaders.

  That matched his own inclinations. His hope of British influence had deep roots. He was the third child among fifteen of a timber merchant who assembled rafts of logs and floated them down the Vistula to Danzig for milling and export. The Weizmanns lived in that impoverished western region of Russia cordoned off for the Jews known as the Pale of Settlement. When Chaim was only eleven he had written a letter that prefigured his work in the war. “The eleven-year-old boy,” reports his biographer Isaiah Berlin, “says that the kings and nations of the world are plainly set upon the ruin of the Jewish nation; the Jews must not let themselves be destroyed; England alone may help them to return and rise again in their ancient land of Palestine.”322

  Young Weizmann’s conviction drove him inexorably west. At eighteen he floated on one of his father’s rafts to West Prussia, worked his way to Berlin and studied at the Technische Hochschule. In 1899 he took his Ph.D. at the University of Fribourg in Switzerland, then sold a patent to Bayer that considerably improved his finances. He moved to England in 1904, a move he thought “a deliberate and desperate step. . . . I was in danger of degenerating into a Luftmensch [literally, an “air-man”], one of those well-meaning, undisciplined and frustrated ‘eternal students.’ ”323 Chemical research would save him from that fate; he settled in Manchester under the sponsorship of William Henry Perkin, Jr., the head of the chemistry department there, whose father had established the British coal-tar dye industry by isolating aniline blue, the purple dye after which the Mauve Decade was named.

  Returning to Manchester from France in late August 1914, Weizmann found a circular on his desk from the British War Office “inviting every scientist in possession of any discovery of military value to report it.” He possessed such a discovery and forthwith offered it to the War Office “without remuneration.”324 The War Office chose not to reply. Weizmann went on with his research. At the same time he began the approach to British leaders that he and Rothschild had discussed that would elaborate into some two thousand interviews before the end of the war.

  Weizmann’s discovery was a bacillus and a process. The bacillus was Clostridium acetobutylicum Weizmann, informally called B-Y (“bacillus-Weizmann”), an anerobic organism that decomposes starch. He was trying to develop a process for making synthetic rubber when he found it, on an ear of corn. He thought he could make synthetic rubber from isoamyl alcohol, which is a minor byproduct of alcoholic fermentation. He went looking for a bacillus—millions of species and subspecies live in the soil and on plants—that converted starch to isoamyl alcohol more efficiently than known strains. “In the course of this investigation I found a bacterium which produced considerable amounts of a liquid smelling very much like isoamyl alcohol.325 But when I distilled it, it turned out to be a mixture of acetone and butyl alcohol in very pure form. Professor Perkins advised me to pour the stuff down the sink, but I retorted that no pure chemical is useless or ought to be thrown away.”

  That creature of serendipity was B-Y. Mixed with a mash of cooked corn it fermented the mash into a solution of water and three solvents—one part ethyl alcohol, three parts acetone, six parts butyl alcohol (butanol). The three solvents could then be separated by straightforward distillation. Weizmann tried developing a process for making synthetic rubber from butanol and succeeded. In the meantime, in the years just prior to the beginning of the war, the price of natural rubber fell and the clamor for synthetic rubber stilled.

  Pursuing his efforts toward a Jewish homeland, Weizmann acquired in Manchester a loyal and influential friend, C. P. Scott, the tall, elderly, liberal editor of the Manchester Guardian. Among his many connections, Scott was David Lloyd George’s most intimate political adviser. Weizmann found himself having breakfast one Friday morning in January 1915 with the vigorous little Welshman who was then Chancellor of the Exchequer and who would become Prime Minister in the middle of the war.326 Lloyd George had been raised on the Bible. He respected the idea of a Jewish return to Palestine, especially when Weizmann eloquently compared rocky, mountainous, diminutive Palestine with rocky, mountainous, diminutive Wales. Besides Lloyd George, Weizmann was surprised to find interest in Zionism among such men as Arthur Balfour, the former Prime Minister who would serve as Foreign Secretary in Lloyd George’s cabinet, and Jan Christiaan Smuts, the highly respected Boer who joined the British War Cabinet in 1917 after serving behind the scenes previously. “Really messianic times are upon us,” Weizmann wrote his wife during this period of early hope.327

  Weizmann had cultured B-Y primarily for its butanol. He happened one day to tell the chief research chemist of the Scottish branch of the Nobel explosives company about his fermentation research. The man was impressed. “You know,” he said to Weizmann, “you may have the key to a very important situation in your hands.”328 A major industrial explosion prevented Nobel from developing the process, but the company let the British government know.

  “So it came about,” writes Weizmann, “that one day in March [1915], I returned from a visit to Paris to find waiting for me a summons to the British Admiralty.”329 The Admiralty, of which Winston Churchill, at fortyone exactly Weizmann’s age, was First Lord, faced a severe shortage of acetone. That acrid solvent was a crucial ingredient in the manufacture of cordite, a propellant used in heavy artillery, including naval guns, that takes its name from the cordlike form in which it is usually extruded. The explosive material that hurled the heavy shells of the British Navy’s big guns from ship to ship and ship to shore across miles of intervening water was a mixture of 64 parts nitrocellulose and 30.2 parts nitroglycerin stabilized with 5 parts petroleum jelly and softened—gelatinized—with 0.8 percent acetone. Cordite could not be manufactured without acetone, and without cordite the guns would need to be extensively rebuilt to accommodate hotter propellants that would otherwise quickly erode their barrels.

  Weizmann agreed to see what he could do. Shortly he was brought into the presence of the First Lord. As Weizmann remembered the experience of meeting the “brisk, fascinating, charming and energetic” Winston Churchill:330

  Almost his first words were: “Well, Dr.
Weizmann, we need thirty thousand tons of acetone. Can you make it?” I was so terrified by this lordly request that I almost turned tail. I answered: “So far I have succeeded in making a few hundred cubic centimeters of acetone at a time by the fermentation process. I do my work in a laboratory. I am not a technician, I am only a research chemist. But, if I were somehow able to produce a ton of acetone, I would be able to multiply that by any factor you chose.” . . . I was given carte blanche by Mr. Churchill and the department, and I took upon myself a task which was to tax all my energies for the next two years.

  That was part one of Weizmann’s acetone experience. Part two came in early June. The British War Cabinet had been shuffled in May because of the enlarging disaster of the Dardanelles campaign at Gallipoli; Herbert Asquith, the Prime Minister, had required Churchill’s resignation as First Lord of the Admiralty and replaced him with Arthur Balfour; Lloyd George had moved from Chancellor of the Exchequer to Minister of Munitions. Lloyd George thus immediately inherited the acetone problem in the wider context of Army as well as Navy needs. Scott of the Manchester Guardian alerted him to Weizmann’s work and the two men met on June 7. Weizmann told him what he had told Churchill previously. Lloyd George was impressed and gave him larger carte blanche to scale up his fermentation process.

  In six months of experiments at the Nicholson gin factory in Bow, Weizmann achieved half-ton scale. The process proved efficient. It fermented 37 tons of solvents—about 11 tons of acetone—from 100 tons of grain. Weizmann began training industrial chemists while the government took over six English, Scottish and Irish distilleries to accommodate them. A shortage of American corn—German submarines strangled British shipping in the First War as in the Second—threatened to shut down the operations. “Horse-chestnuts were plentiful,” notes Lloyd George in his War Memoirs, “and a national collection of them was organised for the purpose of using their starch content as a substitute for maize.”331 Eventually acetone production was shifted to Canada and the United States and back to corn.