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 90 Scientific American January 1997 Copyright 1996 Scientific American, Inc. The Einstein-Szilard Refrigerators MANN T .G. ORBIS-BET ODI, © A.E I/C OR UP T K 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 The Einstein-Szilard Refrigerators Copyright 1996 Scientific American, Inc. Scientific American January 1997 91 a b .G. ODI, © A.E OR T K TESY OF ALBER OUR GENE DANNEN C 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.