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The pressure cooker in many Indian kitchens has a weight on the lid that lifts when the steam pushes hard enough. That idea is more than 340 years old. Denis Papin described it in 1681, together with a calculation of how much pressure the weight would hold. This post looks at what he built, the physics of why it cooks faster, and the lever sum in his own book.
Who was Denis Papin?
The Oxford Dictionary of National Biography lists him as "Papin, Denis (1647–1712?)": even the year of his death is uncertain. A 2024 article in the Comptes Rendus Mécanique of the French Academy of Sciences describes him as a doctor of medicine who never practised, worked as an assistant to Christiaan Huygens and Robert Boyle, and moved from patron to patron because his Protestant faith kept him out of France.
The record of his early work is in the Royal Society's journal. In 1675 the Philosophical Transactions reported experiments in the air pump made by Papin under Huygens's direction. By 1685 his papers carried the line "Dr. Papin, Fellow of the Royal Society".
What was the digester?
In 1681 Papin published A New Digester or Engine for Softning Bones in London. Its long title lists the uses he had in mind: cookery, voyages at sea, confectionery, making drinks, chemistry and dyeing, along with "an account of the price a good big engine will cost".
A French edition followed in Paris in 1682, La manière d'amolir les os, dedicated to the Royal Society of London. In its preface Papin says that Boyle's Latin book of 1680 had already reported some experiments with the screw-closed vessel, but gave neither a description of the machine nor a safe way to use it. So he wrote a separate small treatise for heads of households and craftsmen.
The vessel was a strong metal pot with a lid clamped down by screws. Bones, meat and water went in, the lid went on, and the pot was heated.
Why does food cook faster under pressure?
Water boils when its vapour pressure equals the pressure pressing on it. Raise the pressure and the water must get hotter before it boils. The NIST saturation table for water gives:
100 °C at 101.42 kPa (about 1 atmosphere)
110 °C at 143.38 kPa
120 °C at 198.67 kPa (about 2 atmospheres)
So if a cooker's weight holds the steam at about one atmosphere above the outside air (an illustrative figure, about 2 atmospheres absolute), the water inside sits near 120 °C instead of 100 °C. Cooking reactions speed up sharply with temperature, which is why tough food softens in a fraction of the time.
How did Papin measure the pressure with a lever?
Without a temperature or pressure gauge, a cook could pull food out raw or leave it to burn. Papin's answer, in a section of the French edition headed "pour connoistre la quantité de pression", was a small open tube soldered over a hole in the lid. A valve sat on top of the tube, and an iron rod pressed on the valve like the arm of a steelyard, with a sliding weight. His own numbers make a neat worked example:
Area. The tube was nearly 2/5 inch across. Area scales as diameter squared, so compared with a 1-inch hole the ratio is (2/5)² = 4/25, about one-sixth.
Force from the air. Following Boyle, he took ordinary air pressure on a 1-inch hole as about 12 pounds. A check: 14.7 pounds per square inch times π(0.5 inch)² = 0.785 square inch gives 11.5 pounds. One-sixth of 12 is about 2 pounds on his small tube.
The lever. The rod was 12 inches long and the valve sat 1 inch from the pivot. Taking moments, 1 pound at the far end presses on the valve like 12 pounds sitting on it.
The result. 12 pounds divided by 2 pounds per atmosphere is 6. The valve cannot lift until the pressure inside is about six times ordinary air pressure. Papin added that the rod itself resisted about two more, so when steam escaped with the weight at the end he concluded the pressure was about eight times ordinary.
Common mistakes in this kind of problem: using diameter instead of diameter squared for the area, and forgetting the weight of the lever arm itself, which Papin did not forget. Our post on torque and equilibrium covers taking moments step by step.
What came after the digester?
The Comptes Rendus article notes that Papin went on to set out experimental principles for using steam as a motive force, citing his 1690 paper in Acta Eruditorum on a new way to obtain large driving forces cheaply. Our post on James Watt and the steam engine picks up that later history.
What can a student take from how Papin worked?
Make the danger measurable. He did not just build a strong pot. He built a way to know how hard it was pushing.
Write for the user. He wrote the French book for households and craftsmen, not only for scholars.
Check the numbers. His valve sum uses areas, a lever and a reference pressure, the same steps you use in a JEE-style statics problem.
If moments and pressure still feel abstract, the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read.
Next step: redo Papin's lever sum with a tube 1/2 inch across and find how many atmospheres the same 1-pound weight would hold.
