The Einstein- Szilard Refrigerators

Two visionary theoretical physicists joined forces in the 1920s to reinvent the household refrigerator

by Gene Dannen SanUniversity of California, Diego

n July 1939 Leo Szilard visited Al- ty of Jerusalem), a detailed picture of bert Einstein to discuss the danger the Einstein-Szilard collaboration has I of atomic bombs. Szilard was emerged. The project was more exten- alarmed by the recent discovery of ura- sive, more profitable and more techni- nium fission: he had realized almost six cally successful than anyone guessed. years earlier how a “chain reaction” The story illuminates Einstein’s unlikely could dangerously multiply such a pro- role as a practical inventor. cess. Szilard’s warning that nuclear weapons might be possible—and that Inventing with Einstein Nazi Germany might build them—con- vinced Einstein to write his famous let- zilard and Einstein met in Berlin in LIBRARY MANDEVILLE SPECIAL COLLECTIONS LEO SZILARD PAPERS, ter to President Franklin D. Roosevelt 1920. Einstein, then 41, was already S REFRIGERATOR CABINET (center), seen urging faster research efforts. the world’s most renowned physicist. from the rear, awaits installation of an electro- When Szilard visited Einstein on Long Szilard, at 22, was a brilliant and gregar- magnetic pump invented by Leo Szilard (left) Island, N.Y., that day, he was also reviv- ious Hungarian studying for his doctor- ing a collaboration dating from Berlin’s ate in physics at the University of Berlin. golden age of physics. It is part of the For his dissertation, Szilard extended nized as the cornerstone of information lore of physics that Szilard and Einstein classical thermodynamics to fluctuating theory. In late 1924 Nobel laureate held many joint patents, filed in the late systems, applying the theory in a way Max von Laue selected Szilard to be his 1920s, on ingenious types of home re- that Einstein had said was impossible. assistant at the university’s Institute for frigerators without moving parts. But The “Herr Professor” was impressed, Theoretical Physics. little information beyond the patents and a friendship grew. By the mid-1920s, Szilard had become was thought to survive. After graduation, Szilard later re- a frequent visitor to Einstein’s home. In In the process of researching Szilard’s called, Einstein advised him to take a some ways, the two men were opposites. life, I have been able to piece together job in the patent office. “It is not a good Szilard was outgoing and self-confident almost the full story of this partnership. thing for a scientist to be dependent on (some said arrogant); Einstein was mod- In Stockholm, I discovered that appli- laying golden eggs,” Einstein said. est and retiring. In more important ways, ance manufacturer AB Electrolux still “When I worked in the patent office, however, they were kindred spirits. They keeps files on two patents purchased that was my best time of all.” shared a joy in ideas, a strong social con- from Einstein and Szilard. And in Bu- Despite this suggestion, Szilard chose science—and a fondness for invention. dapest, the primary engineer for the in- an academic career at his alma mater According to the late Massachusetts ventions, Albert Korodi, shared cher- and soon solved the problem of Max- Institute of Technology physicist Ber- ished memories of the enterprise. Koro- well’s Demon. This imp, first imagined nard Feld, who heard the story from di, who died recently at the age of 96, by James Maxwell, could seemingly vi- Szilard, the refrigerator collaboration be- had preserved copies of engineering re- olate the second law of thermodynam- gan with a newspaper article. One day ports—including the only known pho- ics by sorting fast and slow molecules, Einstein read about an entire family— tographs of the Einstein-Szilard proto- thus confounding their natural tenden- parents and several children—who had types—that were long believed lost. cy to become disordered. The demon been killed in their beds by the poison- From these sources and from corre- could then power a perpetual-motion ous gases leaking from the pump of their spondence in the Leo Szilard Papers at machine. Szilard showed that this was refrigerator. At the time, such accidents the University of California at San Di- false: the apparent gain in order was were a growing hazard. Mechanical ego and from the Albert Einstein Ar- supplied by the information used to home refrigerators were starting to re- chives at Princeton University (originals produce the effect. His solution includ- place traditional iceboxes. Chemistry, of the latter are at the Hebrew Universi- ed the idea of a “bit,” later to be recog- however, had yet to produce a nontoxic

and Albert Einstein (right). The refrigerator, developed at

TESY OF ALBER the A.E.G. Research Institute in Berlin, was never marketed,

OUR partly because of the Great Depression. C refrigerant. The three cooling gases then ed young friend, agreed to a collabora- trolux, was considered a breakthrough. commonly used—methyl chloride, am- tion. A letter from Szilard to Einstein Szilard devised an improvement. monia and sulfur dioxide—were all tox- preserves the terms of their agreement. In fact, the entrepreneurs did not stop ic, and the quantities in a refrigerator All inventions by either of them in the with a single design; they came up with could kill. field of refrigeration would be joint many. Einstein’s experience as a patent Einstein was distressed by the tragedy. property. Szilard would have first claim examiner allowed them to do without “There must be a better way,” he said on profits if his income fell below the the usual attorneys, and in early 1926 to Szilard. The two scientists reasoned salary of a university assistant. Other- Szilard began filing a series of patent that the problem was not just the refrig- wise, all royalties would be shared applications on their inventions. By the erant. Such leakages, from bearings and equally. fall, they had decided on the three most seals, were inevitable in systems with promising designs. moving parts. From their knowledge of Early Designs Each refrigerator, it seems, was based thermodynamics, however, they could on an entirely different physical con- derive many ways to produce cooling hen, as now, most refrigerators used cept—absorption, diffusion or electro- without mechanical motion. Why not Tmechanical compressor motors. A magnetism. In a letter to his brother, put these to use? refrigerant gas is compressed, liquefy- Bela, written in October, Szilard de- There was personal incentive to try. ing as its excess heat is discharged to scribed their progress. “The matter of At that time, evidently the winter of the surroundings. When the liquid is al- the refrigerator patents, which I applied 1925–1926, Szilard was preparing to lowed to expand again, it cools and can for together with Professor Einstein, has take the next step in a German academ- absorb heat from an interior chamber. now come so far that I feel it is a reason- ic career—to become a privatdocent, or Einstein and Szilard considered a differ- able time to get into contact with indus- instructor. As an assistant, he received a ent concept, used in so-called absorp- try,” he wrote. “All three machines work salary; as an instructor, however, he tion refrigerators, to be the safer. In these without moving parts, and are hermeti- would be forced to scrape by on small devices, heat from a natural gas flame— cally sealed.... One of these three types fees collected from students. The inven- rather than the push of a piston—drives is nearly identical with one of the Elec- tions, if successful, could support Szi- the cooling cycle. One new design, by trolux company’s machines (in my opin- lard’s budding career. Swedish inventors Baltzar von Platen and ion the best at the moment).... The other Einstein, who wanted to help his gift- Carl Munters, and marketed by AB Elec- two types are completely different from

DIVERSE PRINCIPLES lie behind the Einstein-Szilard refriger- chamber 1 (at right), taking up heat. The gaseous mixture pass- ators. An absorption design (a) purchased by AB Electrolux uses es to chamber 6 (center), where water absorbs the ammonia, a heat source and a combination of fluids to drive the refriger- freeing liquid butane to be recirculated. The electromagnetic ant, butane, through a complex circuit. The butane, initially a pump (b) developed by A.E.G. pushes a liquid metal through a liquid, vaporizes in the presence of ammonia in the refrigerant cylinder; here it is using mercury for test purposes. The any other machines known until now.” er he followed Szilard to Berlin, where even so, Szilard and Einstein earned Szilard quickly negotiated a contract they lived in the same apartment build- roughly $10,000 in today’s dollars. with the Bamag-Meguin company, a ing and became close friends. The application for a U.S. patent on large manufacturer primarily of gas- Unfortunately, the agreement with the absorption device caused some po- work equipment with factories in Ber- Bamag-Meguin lasted less than a year. lite consternation. “I would be interest- lin and Anhalt. In late 1926 Szilard be- “Bamag-Meguin got in difficulties at ed to know if Albert Einstein is the same gan to supervise the development of that time. I think they dropped all un- person who propounded the theory of prototypes at the laboratories of the In- certain projects,” Korodi recalled. With- relativity,” wrote back the American stitute of Technology in Berlin. Albert in months, however, the inventors patent attorney responsible for the case. Kornfeld, a Hungarian graduate from reached agreements with two other com- If so, he continued, the patent office the electrical engineering department of panies, one Swedish and one German. should not object to Einstein’s unusual the institute, started working on the re- The Swedish company was AB Elec- claim of dual Swiss-German citizen- frigerators at this time. (Kornfeld later trolux. On December 2, 1927, Platen- ship: “Albert Einstein is listed in the changed his name to Korodi, and I will Munters Refrigerating System, a divi- Standard Dictionary under the word use that name hereafter.) In 1916 Korodi sion of Electrolux in Stockholm, bought ‘Einstein’ as an adjective denoting a had won the Eötvös Prize, the presti- a patent application for an absorption theory of relativity. The dictionary ex- gious Hungarian mathematics competi- refrigerator from the two inventors for plains that the name is derived from Al- tion for 18-year-old students. After meet- 3,150 reichsmarks, or $750. Both par- bert Einstein, a citizen of both Switzer- ing Szilard through the Eötvös compe- ties were pleased with the transaction. land and Germany. With this designa- tition, Korodi had studied with him at Electrolux’s files show that it consid- tion in one of the accepted dictionaries, the Budapest Technical University. Lat- ered the purchase price “very cheap”; I think the Patent Office will not object

blueprint (c) shows the cylinder lengthwise (above) and in cross tassium-sodium alloy—the pump is the dark vertical cylinder section (below). Alternating current flowing through coils (ar- near the bottom—and a pentane refrigerant. The prominent ar- ranged like spokes of a wheel) provides electromagnetic induc- ray of condenser coils operates the same way as in modern re- tion to drive the liquid, which acts as a piston to compress a refrigerators. The two photographs, from 1932, were recently dis- frigerant. A nearly complete refrigerator assembly (d) uses a po- covered by the author. to the statement that Prof. Einstein is a The device, Korodi recalled, was “a tail quantities did not turn out to be as citizen of two different countries.” small immersion cooler that could be cheap as expected. But more important, Electrolux also later purchased the dipped for instance in a cup of some the ingenious cooler, which required re- diffusion design; the patent it took out beverage to be cooled.” Requiring no liable water pressure, met its match in on this invention, however, does not conventional power source, it operated the haphazard German water system. mention Einstein or Szilard. Nor did solely off the pressure of a water tap. At the time, the pressure of tap water Electrolux ever develop either of the two The pressure powered a water-jet pump, varied between buildings as well as patents. The documents show that, de- producing a vacuum in a chamber from from floor to floor within a building. In spite admiration for their ingenuity, the which water and a small amount of the end the variations proved too great, firm bought the designs mostly to safe- methanol were evaporated. The metha- and the invention was not marketed. guard their own pending applications. nol was slowly used up, but the liquid Another, much different Einstein-Szi- was cheap and readily available. It could The Einstein-Szilard Pump lard design produced a partnership with be expended and replaced, Korodi ex- the Citogel company in Hamburg (the plained: “That was the idea of Einstein.” he most revolutionary, and most company’s name means “quick freeze” The cooler worked well, and a proto- Tsuccessful, invention would become in Latin). According to Korodi, the in- type was demonstrated under the Cito- known as the Einstein-Szilard electro- vention was Einstein’s response to the gel name at the Leipzig Fair in early magnetic pump. It was a fully function- diabolical complexity of absorption de- 1928. Korodi, who moved to Hamburg al pump without mechanical moving signs: “[He] proposed a quite simple to work with Citogel on the invention, parts. Instead a traveling electromagnet- and cheap system especially suited for remembered Szilard’s exasperation at ic field caused a liquid metal to move. small refrigerators.” the eventual outcome. Methanol in re- The metallic fluid, in turn, was used as

The Einstein-Szilard Refrigerators Copyright 1996 Scientific American, Inc. Scientific American January 1997 93 WATER PRESSURE from a reer. At the University of Berlin, Szilard tap drives this small cooling was teaching seminars in quantum the- device, developed (in simpler ory and theoretical physics with John form) by Citogel in Hamburg. von Neumann and Erwin Schrödinger. Methanol contained in cham- His other inventions during this period ber 3 evaporates in chamber 2, cooling the surrounding included the linear accelerator, cyclo- compartment 13. Turbine 14 tron and electron microscope. Einstein, churns ice cream or other meanwhile, continued his tireless pur- frozen foods. The methanol suit of the Uniﬁed Field Theory but also dissolves in water in chamber worked with other inventors on a gyro- 1 and ﬂows out, so it has to be compass and a hearing aid. replenished. The device was Even as the refrigerator advanced, not marketed because of vari- however, dark clouds were gathering.

able water pressure in German In the Reichstag elections of September . buildings.

14, 1930, the tiny Nazi party received U.C.S.D Y

almost 20 percent of the vote. Szilard, AR with his legendary foresight, saw what ity. “It was worthwhile to others did not. On September 27 he make such a compressor,” wrote to Einstein with a prophetic warn- OLLECTIONS LIBR he stated: an Einstein-Szilard ing: “From week to week I detect new pump would not leak or fail. symptoms, if my nose doesn’t deceive ECIAL C In the fall of 1928 the All- me, that peaceful [political] develop- VILLE SP gemeine Elektrizitäts Gesell- ment in Europe in the next ten years is schaft (German General Elec- not to be counted on.... Indeed, I don’t ERS, MANDE

tric Company), or A.E.G., know if it will be possible to build our AP agreed to develop the pump refrigerator in Europe.” ARD P for refrigeration. The A.E.G.

was a prosperous Berlin firm A Working Refrigerator LEO SZIL with its own research insti- a piston to compress a refrigerant. (The tute, where it established a special de- ntil recently, the only known detail refrigerant cycle, after that point, was partment led by two full-time engineers. Uof the Einstein-Szilard electromag- the same as in standard refrigerators.) Korodi was hired to develop electrical netic pump prototype was its objection- Korodi remembered vividly that the aspects of the invention. Another Hun- able noise. Although expected to be si- device was first envisioned as an elec- garian engineer friend of Szilard’s, Lazi- lent, the pump suffered from cavita- tromagnetic conduction pump, with an slas Bihaly, was taken on to develop the tion—the expansion and collapse of tiny electric current passing through the liq- mechanical side. Szilard, with the title voids or cavities—as the liquid metal was uid metal. Mercury was an obvious first of consultant, directed the team. forced through the pump. Physicist Den- choice, but its low conductivity would Korodi and Szilard received salaries nis Gabor, who was one of Szilard’s best provide very poor efficiency. Szilard then of 500 reichsmarks a month, the equiv- friends in Berlin, once commented that suggested an alternative liquid metal—a alent of $120. “It was a good salary,” the pump “howled like a jackal.” An- potassium-sodium alloy with much bet- Korodi observed, at a time when “a car, other “earwitness,” according to Amer- ter conductivity. Although potassium a Ford, cost $300.” For Szilard, the ican physicist Philip Morrison, said it and sodium were both solids at room A.E.G. contract was even more lucra- wailed “like a banshee.” temperature, an optimal mixture of the tive. Patent royalties, in addition to his Korodi, on the other hand, described two was liquid above its melting point consulting fees, eventually brought his the sound as resembling that of rushing of –11 degrees Celsius. Unfortunately, income to a comfortable $3,000 a year water. Furthermore, as detailed in the the metals were chemically aggressive (worth roughly $40,000 today). A.E.G. final report, the noise depended and would attack the insulation of the Szilard and Einstein kept a joint on the force and speed of the pump. A wires carrying current to the mixture. bank account, but the sum Einstein ac- combination of tricks—reducing the Szilard and Korodi considered differ- tually accepted from the partnership re- voltage at the start of each stroke, for ent insulating materials, then Szilard mains unknown. Korodi described Ein- example—eventually lowered the noise took the problem back to Einstein. “Ein- stein as far from a silent partner, how- to acceptable levels. stein thought a few minutes,” Korodi ever: he visited the laboratory at each From an engineering viewpoint, the related, and proposed eliminating the stage of construction to check on the noise problem was mostly cosmetic. need for such wires by applying indirect prototypes. Korodi also remembered The truly interesting challenges arose in force from exterior coils, by induction. visiting Einstein’s Berlin apartment with working with chemically reactive met- The invention therefore became an Szilard, perhaps a dozen times, to talk als. Special equipment was developed induction pump. Korodi, who calculat- about new inventions. “I didn’t talk to to fill the pump without the (possibly ed the expected efficiency of the pump Einstein about physics,” he recalled with explosive) oxidation of the sodium and for potassium-sodium alloys, found that a laugh. potassium. Despite this difficulty, Koro- it was still much less efficient than stan- For Szilard, who did discuss physics di emphasized that there would have dard compressors. What it lacked in with Einstein, the collaboration was been no danger to refrigerator owners. efficiency, however, it gained in reliabil- funding an increasingly productive ca- The Einstein-Szilard refrigerator was a

94 Scientific American January 1997 Copyright 1996 Scientific American, Inc. The Einstein-Szilard Refrigerators sealed system, with the liquid metals ful- avail. In 1932 the A.E.G. Research In- ly contained in welded stainless steel. stitute was reduced by half, eliminating Many problems had been solved, but all but essential projects. Korodi helped the noise was still under attack, when a to write the 104-page final report on full prototype was constructed. “In two the Einstein-Szilard refrigerator devel- years,” Korodi stated, “a complete re- opment: A.E.G. Technischer Bericht frigerator was built, which worked— 689, dated August 16, 1932. (It is for- operated—as a refrigerator.” On July tunate that Korodi kept a copy of this 31, 1931, an Einstein-Szilard refrigera- manuscript, because the A.E.G.’s files tor went into continuous operation at were destroyed in World War II.) the A.E.G. Research Institute. For com- Only months later Adolf Hitler’s ap- parison with existing units, the appara- pointment as chancellor ended Berlin’s tus was mounted in the cabinet of a golden age of physics. Szilard fled to four-cubic-foot (120-liter) General Elec- Britain and then to America. Einstein tric model G40 refrigerator. With a po- found refuge at the Institute for Ad- tassium-sodium alloy as its liquid metal vanced Study in Princeton, N.J. Korodi and pentane as a refrigerant, the proto- returned to Budapest, where he found type operated at 136 watts, consuming work with the Hungarian division of 2.3 kilowatt-hours a day. Philips and built a successful career in “The efficiency was as good as it was telecommunications. He died in Buda- calculated,” Korodi insisted. But for the pest on March 28, 1995. A.E.G., battered by the growing world- wide depression, the refrigerator was Applied Physics not good enough. Improvements in con-

ventional refrigerators, in addition to n the seven years of their collabora- ULSON A the economic slump, were shrinking the tion, Szilard and Einstein ﬁled more I AM P potential market. The 1930 American than 45 patent applications in at least OL GR AR

demonstration of a nontoxic “Freon” six countries. Although none of their C refrigerant, in particular, promised to refrigerators reached consumers, the eliminate the danger of leaks. (Only de- designs were ingenious applications of ALBERT KORODI (1898–1995) was the cades later, of course, would it be real- physical principles. The Einstein-Szilard primary engineer for the inventions. He is holding the Tivadar Puskás Award of the ized that such chlorofluorocarbons might pump, in particular, eventually proved Hungarian Scientific Society for Telecom- endanger the ozone layer of the entire its value. The built-in safety of its de- munications, which he received in 1993. planet.) sign later found a more critical task in Work continued in the A.E.G. labo- cooling breeder reactors. ratory for another year, resulting in im- As intended, the inventions had sup- chosen to design refrigerators. Today, proved pump prototypes and a change ported Szilard’s academic career in Ger- with refrigeration technology again a in liquid metals. The internal heat of many. His savings, moreover, saw him priority—this time the earth’s ozone lay- the pump had proved sufficient to keep through two more years in Britain. Af- er might be at stake—the challenge of pure potassium above its melting point ter selflessly helping fellow refugee schol- the problem has become clear. For Szi- of 63 degrees C. A four-month-long test ars find university positions, he turned lard and Einstein, the inventions were operation with potassium was success- to nuclear physics and conceived the more than a brief interlude. From their ful, increasing the electrical efficiency neutron chain reaction in the autumn of first collaboration in physics to their lat- from 16 to 26 percent. The Depression- 1933. Szilard’s early research on atomic er efforts in controlling the threat of nu- ravaged A.E.G., however, was not per- energy was in fact made possible by clear weapons, Szilard’s and Einstein’s suaded to continue the research. this money. scientific accomplishments and their Szilard tried to interest manufactur- For decades, it seemed a mere curios- commitment to humanity were closely ers in Britain and America, also to no ity that Szilard and Einstein should have intertwined. SA

The Author Further Reading

GENE DANNEN is an independent scholar who has The Collected Works of Leo Szilard: Scientific Papers. Edited by been researching the life of Leo Szilard for 15 years. This Bernard T. Feld and Gertrud Weiss Szilard. MIT Press, 1972. article is adapted from his forthcoming book on Szilard’s Leo Szilard: His Version of the Facts; Selected Recollections and role in the birth of the nuclear age. He owes special thanks Correspondence. Edited by Spencer R. Weart and Gertrud Weiss Szilard. to the Mandeville Special Collections Library at the Univer- MIT Press, 1978. sity of California, San Diego; the department of rare books Einstein as Inventor. Georg Alefeld in Physics Today, Vol. 33, No. 5, and manuscripts at Princeton University Libraries; Egon pages 9–13; May 1980. Weiss for permission to use Szilard’s unpublished letters; Handbook of Electromagnetic Pump Technology. Richard S. Baker Henry Throop and Carol Paulson for conducting inter- and Manuel J. Tessier. Elsevier, 1987. views with Albert Korodi; and Mihály Korodi. Dannen can The author maintains a Leo Szilard Page on the World Wide Web at be reached by e-mail at [email protected] http://www.peak.org/~danneng/szilard.html