Benoît Paul Émile Clapeyron (; 26 January 1799 – 28 January 1864) was a French

engineer Engineers, as practitioners of engineering, are professionals who Invention, invent, design, build, maintain and test machines, complex systems, structures, gadgets and materials. They aim to fulfill functional objectives and requirements while ...

and

physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...

, one of the founders of

thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed b ...

Life

Born in

Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...

, Clapeyron studied at the

École polytechnique (, ; also known as Polytechnique or l'X ) is a ''grande école'' located in Palaiseau, France. It specializes in science and engineering and is a founding member of the Polytechnic Institute of Paris. The school was founded in 1794 by mat ...

, graduating in 1818. He also studied at École des mines. In 1820 he and

Gabriel Lamé Gabriel Lamé (22 July 1795 – 1 May 1870) was a French mathematician who contributed to the theory of partial differential equations by the use of curvilinear coordinates, and the mathematical theory of elasticity (for which linear elasticity ...

went to

Saint Petersburg Saint Petersburg, formerly known as Petrograd and later Leningrad, is the List of cities and towns in Russia by population, second-largest city in Russia after Moscow. It is situated on the Neva, River Neva, at the head of the Gulf of Finland ...

to teach and work at the school of public works there. He returned to Paris only after the Revolution of July 1830, supervising the construction of the first

railway Rail transport (also known as train transport) is a means of transport using wheeled vehicles running in railway track, tracks, which usually consist of two parallel steel railway track, rails. Rail transport is one of the two primary means of ...

lines connecting Paris to

Versailles The Palace of Versailles ( ; ) is a former royal residence commissioned by King Louis XIV located in Versailles, Yvelines, Versailles, about west of Paris, in the Yvelines, Yvelines Department of Île-de-France, Île-de-France region in Franc ...

and Paris to Saint-Germain. The half brothers Stéphane Mony and Eugène Flachat collaborated in this project, which was financed by Adolphe d'Eichthal^{( fr)},

Rothschild Rothschild () is a name derived from the German ''zum rothen Schild'' (with the old spelling "th"), meaning "to the red shield", in reference to the houses where these family members lived or had lived. At the time, houses were designated by signs ...

, Auguste Thurneyssen, Sanson Davillier and the Péreire brothers. Clapeyron took his

steam engine A steam engine is a heat engine that performs Work (physics), mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a Cylinder (locomotive), cyl ...

designs to England in 1836 to find a manufacturer and engaged Sharp, Roberts and Co. From 1844 to 1859 Clapeyron was a professor at École des Ponts et Chaussées. Clapeyron married Mélanie Bazaine, daughter of Pierre-Dominique Bazaine (mathematician and ingénieur des ponts), and older sister of Pierre-Dominique (Adolphe) Bazaine (railway engineer) and

François Achille Bazaine François Achille Bazaine (13 February 181123 September 1888) was an officer of the French army. Rising from the ranks, during four decades of distinguished service (including 35 years on campaign) under Louis-Philippe I, Louis-Philippe and then ...

(Marshal of France).

Work

In 1834, he made his first contribution to the creation of modern thermodynamics by publishing a report entitled ''Mémoire sur la puissance motrice de la chaleur'' (''Memoir on the Motive Power of Heat''), in which he developed the work of the physicist

Nicolas Léonard Sadi Carnot Nicolas Léonard Sadi Carnot (; 1 June 1796 – 24 August 1832) was a French people, French military engineering, military engineer and physicist. A graduate of the École polytechnique, Carnot served as an officer in the Engineering Arm (''le ...

, deceased two years before. Though Carnot had developed a compelling analysis of a generalised

heat engine A heat engine is a system that transfers thermal energy to do mechanical or electrical work. While originally conceived in the context of mechanical energy, the concept of the heat engine has been applied to various other kinds of energy, pa ...

, he had employed the clumsy and already unfashionable

caloric theory The caloric theory is an obsolete scientific theory that heat consists of a self-repellent fluid called caloric that flows from hotter bodies to colder bodies. Caloric was also thought of as a weightless gas that could pass in and out of pores ...

. Clapeyron, in his memoire, presented Carnot's work in a more accessible and analytic graphical form, showing the

Carnot cycle A Carnot cycle is an ideal thermodynamic cycle proposed by French physicist Nicolas Léonard Sadi Carnot, Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. By Carnot's theorem (thermodynamics), Carnot's theorem, it provides ...

as a closed

curve In mathematics, a curve (also called a curved line in older texts) is an object similar to a line, but that does not have to be straight. Intuitively, a curve may be thought of as the trace left by a moving point. This is the definition that ...

on an

indicator diagram An indicator diagram is a chart used to measure the thermal, or cylinder, performance of Reciprocating engine, reciprocating steam and Internal combustion engine, internal combustion engines and compressors. An indicator chart records the press ...

, a

chart A chart (sometimes known as a graph) is a graphics, graphical representation for data visualization, in which "the data is represented by symbols, such as bars in a bar chart, lines in a line chart, or slices in a pie chart". A chart can repres ...

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

against

volume Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...

(named in his honor Clapeyron's graph). Clapeyron's analysis of Carnot was more broadly disseminated in 1843 when Johann Poggendorff translated it into German. In 1842 Clapeyron published his findings on the "optimal position for the piston at which the various valves should be opened or closed." In 1843, Clapeyron further developed the idea of a reversible process, already suggested by Carnot and made a definitive statement of ''Carnot's principle'', what is now known as the

second law of thermodynamics The second law of thermodynamics is a physical law based on Universal (metaphysics), universal empirical observation concerning heat and Energy transformation, energy interconversions. A simple statement of the law is that heat always flows spont ...

. These foundations enabled him to make substantive extensions of Clausius' work, including the formula, now known as the

Clausius–Clapeyron relation The Clausius–Clapeyron relation, in chemical thermodynamics, specifies the temperature dependence of pressure, most importantly vapor pressure, at a discontinuous phase transition between two phases of matter of a single constituent. It is nam ...

, which characterises the

phase transition In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic Sta ...

between two phases of

matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic pa ...

. He further considered questions of phase transitions in what later became known as Stefan problems. Clapeyron also worked on the characterisation of

perfect gas In physics, engineering, and physical chemistry, a perfect gas is a theoretical gas model that differs from real gases in specific ways that makes certain calculations easier to handle. In all perfect gas models, intermolecular forces are neglecte ...

es, the equilibrium of homogeneous

solid Solid is a state of matter where molecules are closely packed and can not slide past each other. Solids resist compression, expansion, or external forces that would alter its shape, with the degree to which they are resisted dependent upon the ...

s, and calculations of the

statics Statics is the branch of classical mechanics that is concerned with the analysis of force and torque acting on a physical system that does not experience an acceleration, but rather is in mechanical equilibrium, equilibrium with its environment ...

of continuous beams, notably the theorem of three moments (Clapeyron's

theorem In mathematics and formal logic, a theorem is a statement (logic), statement that has been Mathematical proof, proven, or can be proven. The ''proof'' of a theorem is a logical argument that uses the inference rules of a deductive system to esta ...

Honors

*Member of the

Académie des Sciences The French Academy of Sciences (, ) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French Scientific method, scientific research. It was at the forefron ...

, (1858). *The Rue Clapeyron in

' 8th arrondissementbr>(here)
is named for him. *His name is one of the 72 names inscribed on the Eiffel Tower.

Publications

* * (source
The Internet Archive

References

External links

* {{DEFAULTSORT:Clapeyron, Benoit Paul Emile 1799 births 1864 deaths Scientists from Paris French physicists Thermodynamicists École Polytechnique alumni Mines Paris - PSL alumni Corps des mines Members of the French Academy of Sciences Corresponding members of the Saint Petersburg Academy of Sciences French fluid dynamicists