Berthelot, Marcellin (1827-1907), a French chemist, is best remembered for his work on organic synthesis and in thermo-chemistry.

Pierre Eugene Marcellin Berthelot was the son of a doctor who tended the poor of Paris. Berthelot was a shy but brilliant student who at 19 won first prize for philosophy in a national competition. After completing courses in the faculties of medicine and science at the Sorbonne in 1849, he gained practical experience in a private chemistry laboratory. Although he earned a small salary while filling the post of laboratory instructor at the College de France, Berthelot was over 30 before he became financially independent of his none-too-wealthy father. In 1859, he was appointed to the chair of organic chemistry at the School of Pharmacy in Paris, from which he had graduated with a degree in pharmacy the previous year. In 1865, he was appointed to the chair of organic chemistry at the College de France, and for the rest of his life when he was in Paris he worked on a daily basis at his laboratory there.

During the city's siege in the Franco-Prussian War (1870-1871), Berthelot became president of the Scientific Committee for the Defense of Paris. Although he had not put forth his candidacy, he nonetheless was elected to the Senate in 1871. Three years later, he was appointed to a war ministry explosives commission, and in 1878, he became president of its successor. In 1881, the Senate elected Berthelot to a permanent senatorial seat. Among the cabinet positions he held were minister of education (1886-1887) and foreign minister (1895), each for only a few months.

Berthelot's political activities did not keep him from carrying out important research in many fields of chemistry that resulted in 1,600 publications. His contributions to organic chemistry are the most important. For his thesis in 1854, he demonstrated that glycerol is a triatomic alcohol. He was able to synthesize fats, including some that do not occur naturally, by combining glycerol with fatty acids. This work, completed when he was still in his 20's, supported the view that organic chemistry deals with all carbon compounds, not only those formed and found in nature. Next Berthelot investigated sugars, identifying them as both alcohols and aldehydes. Among the many simple organic compounds he succeeded in synthesizing are methane, methyl alcohol (methanol), formic acid (methanoic acid), ethyl alcohol (ethanol), acetylene (ethyne), and benzene. Berthelot also synthesized the hydrocarbons naphthalene and anthracene. In 1860, he summarized his previous decade's work in Organic Chemistry Based on Synthesis. Although the methods were crude and the yields low, Berthelot's preferred synthesizing techniques were reduction using red-hot copper and silent electric discharge.

Berthelot's interest in using an acid and an alcohol to create esters led him to study the kinetics of reversible reactions. Together with Péan de Saint Gilles, he produced an equation for the reaction velocity in 1862. Although the equation was incorrect, it stimulated University of Oslo chemists Cato Guldberg and Peter Waage to present the law of mass action in 1864.

In 1864, Berthelot began his studies of thermochemistry, which deals with the relationship between chemical action and heat. He had already established in 1856, in the course of his investigations of esters, that an ester's heat of combustion is almost exactly equal to the sum of the heats of combustion of the alcohol and acid from which it is formed. He went on to establish several principles about the heat involved in chemical changes. Best known is Berthelot's third principle or law of maximum work : “Every chemical change accomplished without the intervention of energy from outside tends toward the production of a body or system of bodies which produce the most heat.” The Danish chemist Julius Thomsen had independently arrived at the same principle in 1853, 20 years earlier than Berthelot. Although the principle was soon recognized as strictly true only at a temperature of absolute zero, Berthelot and Thomsen share the honor of inaugurating a new epoch in thermochemistry.

Berthelot's thermochemical research led him to invent the bomb calorimeter, an apparatus consisting of a strong container in which a sample of fuel or food is sealed with excess oxygen and ignited electrically. The heat of combustion, or calorific value, can be calculated from the resulting rise in temperature more accurately than had been possible before then. In an 1879 book, Chemical Mechanics, the terms “exothermic” to describe a reaction that releases heat and “endothermic” for one that absorbs heat, appeared in print for the first time. Berthelot had previously introduced the terms in his lectures at the Collége de France. Chemical Mechanics, along with Berthelot's 1897 Thermochemistry, provided the underpinnings of thermochemical science.

While presiding over the scientific commission set up to help defend Paris during the Franco-Prussian War (1870-1871), Berthelot investigated the extraction of saltpeter for gunpowder. In the following decade, he studied the thermochemistry of nitrogen compounds used to make explosives. Together with French ordnance engineer Paul Vieille, Berthelot laid the foundations of a new scientific study of the mechanism of explosions. Berthelot and Vieille noted that low velocity flames propagating in a reactive gaseous mixture could suddenly acquire very high velocities, accompanied by a dramatic rise in temperature and pressure near the flame front. Vieille and Berthelot thus discovered the detonation wave, an extremely strong shock wave closely followed by an exothermic reaction capable of providing enough energy to sustain it. Berthelot was adamant that his explosives research could have peacetime applications. In 1896, in the wake of accidents with liquid acetylene used for lighting, he and Vieille worked together to investigate how acetylene could be used safely.

During the final 25 years of his career, Berthelot conducted important research in agricultural chemistry. In 1883, he established an agricultural station outside Paris in Meudon. There he rediscovered the role that microorganisms play in the fixation of nitrogen in soils. In 1893, he succeeded in isolating and preparing a culture of such microorganisms. He summarized his work in this field in his 1899 book, Vegetable and Agricultural Chemistry .

Berthelot not only made significant advances in chemistry but also illuminated its history. His analysis of ancient metallic objects from Mesopotamia and Egypt, which he visited in 1869 on the occasion of the opening of the Suez Canal, was crucial to the development of chemical archaeology. In 1889, the centennial of the French Revolution (1789-1799) was celebrated. As secretary of the French Academy of Sciences, to which he had been elected in 1873, Berthelot was asked to commemorate French scientists. In response he wrote a book about the pioneering chemist Antoine Laurent Lavoisier and the revolution in chemistry. Berthelot's publication of extracts from Lavoisier's lab notebooks was an important contribution to the history of science.

Over the years, Berthelot also developed his ideas about science as a comprehensive philosophy in books on the relationships between science and philosophy (1886), morality (1897), education (1901), and free thought (1905). He believed that by the year 2000, science would bring about a state of Utopia, and that in this ideal world, chemistry would play a central role by making the best use possible of the earth's natural resources and agricultural potential.

In 1861, Berthelot married Sophie Caroline Niaudet, a descendant of the renowned Swiss-born clockmaker Abraham-Louis Breguet. They had six children. Berthelot died within hours of his wife's death. By special law of Parliament, the couple was interred together in the Panthéon, the national monument in Paris used as a sepulcher for eminent French individuals.