In 1926, Albert Einstein read a Berlin newspaper article about a family — including several children — killed by toxic fumes leaking from their refrigerator's mechanical seal. Early refrigerators used gases like methyl chloride and sulfur dioxide as coolants, and when the pump seals failed, the results were lethal. Einstein was disturbed enough to do something about it.

He called his former student, the Hungarian physicist Leo Szilard (who would later help conceive the nuclear chain reaction), and the two spent the next several years designing refrigerators that had no moving parts whatsoever — meaning no seals that could fail and leak poison gas.

The result was US Patent 1,781,541, filed on December 16, 1927, and granted on November 11, 1930. It describes an absorption refrigerator that uses heat as its only energy input. Instead of a mechanical compressor driven by an electric motor, the Einstein-Szilard design uses pressurized butane, ammonia, and water in a closed loop. Heat applied to one chamber drives a thermodynamic cycle that absorbs heat from another chamber, producing a cooling effect. No pistons. No compressors. No seals. Nothing moves except the fluid itself.

The physics is elegant: liquid butane evaporates in a low-pressure environment (absorbing heat and creating cold), ammonia gas is used to manipulate the partial pressure so the butane evaporates at useful temperatures, and an external heat source drives the ammonia back out of solution to restart the cycle. The entire system is hermetically sealed with no mechanical weak points.

Einstein and Szilard actually filed 45 patent applications across several countries for various refrigerator designs between 1926 and 1933. The collaboration produced three distinct approaches: absorption, diffusion, and electromagnetic pump designs. But none of them reached mass production. The reason? In 1930, Freon was introduced — a non-toxic refrigerant that made mechanical compressors safe enough for home use. The Einstein-Szilard refrigerator was suddenly a solution to a problem that no longer existed.

Then the world changed again.

Freon and its CFC relatives turned out to be destroying the ozone layer. Modern HFC refrigerants are potent greenhouse gases — some with a global warming potential thousands of times greater than CO2. And mechanical compressors still require electricity, typically from fossil fuels. Suddenly, a refrigerator that runs on heat — including solar thermal energy, waste heat from industrial processes, or even a simple gas flame — looks remarkably attractive.

Researchers at Oxford University revived the Einstein-Szilard design in 2008, led by Malcolm McCulloch, and demonstrated a working prototype using modern materials. Their updated version replaced butane with more environmentally friendly pressurizing gases. The key advantage for the developing world is striking: these refrigerators can run on solar heat, need no electricity, have no moving parts to break, and can keep vaccines cold in remote clinics where grid power is unreliable or nonexistent.

The design also has applications in spacecraft thermal management, where mechanical compressors are a reliability risk, and in off-grid housing, where waste heat from cooking or heating could drive cooling for food storage. Several startups as of the mid-2020s are exploring thermally-driven cooling based on absorption cycles directly descended from the Einstein-Szilard concept.

There is something poetic about a patent born from a newspaper tragedy in Weimar-era Berlin — designed by arguably the greatest physicist who ever lived — sitting dormant for nearly a century, only to become relevant again because the "better" solution turned out to be an environmental catastrophe.