Berthelot, Pierre Eugène Marcellin¹

(b. Paris, France, 25 October 1827; d. Paris, 18 March 1907)

chemistry.

His father, Jacques Martin Berthelot, had married Ernestine Sophie Claudine Biard in 1824. Marcellin was the second of three children; the first died in infancy. The father, who was from a family of ironsmiths in the region of Orléans, had come to Paris in 1822 to study medicine. After qualifying he spent most of his life tending the sick in the poorer districts of Paris. Only in his heroic work during the cholera epidemic of 1832, about which he wrote a book, did he rise above obscurity. His income was just sufficient to support his family, and his wife, who came from the bourgeoisie, brought only a small dowry.

At the age of eleven Marcellin Berthelot entered the College Henri IV in Paris. He showed himself reserved in the extreme but brilliant at his lessons, distinguishing himself particularly in Latin verse. In 1846 he won first prize for philosophy among pupils from lycées throughout France. At fourteen Berthelot became a boarder; four years later he met Ernest Renan, whose room was adjacent to his in the pension. Renan was twenty-two and was employed as an assistant master. In 1847 Berthelot became bachelierés lettres and then attended courses in the Paris Faculty of Medicine and the Faculty of Science, graduating from the latter in July 1849. He undertook a rigorous program of reading, including languages and the main branches of science. Berthelot asserted his independence by deliberately avoiding the two great educational institutions, the École Polytechnique and the École Normale, the training ground of so many French men of science. He obtained entry to the private laboratory of the chemist Pelouze, where he learned some practical chemistry. In February 1851 there was a vacancy for the post of demonstrator to Balard at the Collège de France. Berthelot accepted the post although it carried only a nominal salary; in his spare time he prepared for his doctorate. On 24 June 1854 he defended his thesis, “Mémoire sur les combinaisons de la glycérine avec les acides et sur la synthése des principes immédiats des graisses des animaux.” Berthelot carried out further studies at the École de Pharmacie in Paris, graduating as a pharmacist on 29 November 1858. He also visited Italy and Germany during this time. Thus, until he was over thirty, Berthelot lived the life of a student, relying on his father for financial support.

Berthelot became a leading advocate in France of science as an ideal with direct moral implications. Although his parents were Roman Catholic and brought him up in the same faith, he reacted to his philosophy course at school by soon questioning the validity of religion and becoming a skeptic. In this he was influenced by Renan but also by his republican feelings, since the Roman Catholic Church in mid-nineteenth-century France was unsympathetic to radical thought. In his later writings Berthelot attacked clerical influence, particularly in education.

On 30 May 1861 Berthelot married Sophie Caroline Niaudet, a girl from a Protestant family and ten years Younger than he. His wife was a descendant of the famous clockmaker Breguet. The couple had six children. They were devoted to each other for forty-five years, and within an hour of the death of Sophie Berthelot, Marcellin, who had tended her night and day, also died. A special law was passed to permit Berthelot and his wife to be buried together in the Panthéon.

Berthelot was appointed to a chair of organic chemistry created at the École de Pharmacie on 2 December 1859. The success of his book La chimie Organique fondée sur la synthése resulted in his giving a course of lectures at the College de France (1863–1864), and on 8 August 1865 this course was attached to a chair of organic chemistry entrusted to Berthelot. From that time until his death, if Berthelot was in Paris he went daily to his laboratory at the Collège de France. Although he gave more attention to research than to teaching, he had a number of distinguished students, including Jungfteisch, Sabatier, and A. Werner. Berthelot was elected to the Académie de Médecine in 1863, and the Académie des’ Sciences (after three unsuccessful attempts) in 1873. He was made permanent secretary of the latter in 1889. He became a member of the Académie Française in 1901. First nominated as chevalier of the Legion of Honor in 1861, he received the highest grade, Grand-Croix, in 1900. He was also a member of a large number of foreign Académies.

When Paris came under siege in the Franco-Prussian War (1870–1871), Berthelot was made president of the Comité Scientifique pour la Défense de Paris. His activities during the siege of Paris called much attention to himself, and in the election of 1871 he was given a large vote, although he had not put himself forward as a candidate. He first took his seat in the Senate in 1871. In 1874 he was appointed to a War Ministry commission on explosives, and in 1878, when a new commission on explosives was formed, Berthelot was named president. In July 1881 the Senate elected him to a permanent senatorship. Berthelot sat with the parties on the Left and spoke frequently on educational matters. In 1886 he presided over a commission on the laicization of primary education. Berthelot was minister of education from 11 December 1886 to 30 May 1887 in the cabinet of René Goblet. In 1895 he was appointed foreign minister in the cabinet of Léon Bourgeois but resigned after five months because of disagreements over policy on Egypt and the Sudan.

In 1869, on the occasion of the opening of the Suez Canal, Berthelot visited Egypt, the country traditionally associated with the birth of chemistry; but it was not until 1884 that he committed to paper a few ideas on alchemy. Attracted both by the mysticism of the alchemists and by the connection of other parts of their art with the rational science he professed he began, to use his knowledge of Greek to interpret unpublished alchemical manuscripts. Like Hermann Kopp, Berthelot took the view that alchemy had developed as a misunderstanding of the earlier empirical knowledge of Egyptian metalworkers. He and Kopp were the two nineteenth-century figures who were able not only to make outstanding contributions to chemistry but also to undertake an extensive study of its history. Berthelot studied the transmission of ancient alchemy to the Middle Ages. He distinguished a practical tradition, exemplified by the Liberignium of Marcus Graecus, from a theoretical approach transmitted through Syriac and Arabic sources. He argued that the Latin author Geber was distinct from Jābir ibn Ḥayyān. In much of his alchemical studies Berthelot was dependent on his collaborators, who translated the original Syriac and Arabic manuscripts. His interpretation was, therefore, not faultless.

On a more practical plane, Berthelot’s analysis of metallic objects from ancient Egypt and Mesopotamialaid the foundations of chemical archaeology. In 1889, to celebrate the centenary of the French Revolution, Berthelot, as secretary of the Académie des Sciences, was called upon to commemorate men of science. He prepared material for a lecture on Lavoisier, and on the basis of this and Grimaux’s study of 1888 he produced a book, La révolution chimique, Lavoisier. One detects special sympathy by the patriotic nineteenth-century French chemist for the eighteenth-century liberal who had also used his scientific knowledge to help his country. Berthelot’s publication of extracts from the laboratory notebooks of Lavoisier, which were in the possession of the Academy, performed a valuable service to the history of science. Whatever criticisms may be leveled at Berthelot’searlier publications on the history of chemistry, this study was an astonishing achievement for a man who was simultaneously carrying out important research on thermochemistry and agricultural chemistry.

In the last years of his life Berthelot published books that suggest his concept of science as an all-embracing philosophy: Science et philosophie (1886), Science et morale (1897), Science et education (1901), Science et libre pensée (1905). He regarded it as unreasonable to assign limits to the possible progress of science. He foresaw a Utopia through science that could be realized by the year 2000. In this new world he considered chemistry to have a central place not only because of its almost unlimited powers of synthesis but also through the exploitation of agriculture and natural resources. Berthelot continually fought against clerical influence in education. He wanted a greater place for science in the school curriculum, but not at the expense of classical studies. The moral value of science for Berthelot lay not only in its respect for truth but also in its justification for work. Berthelot, like Claude Bernard, favored a positivistic philosophy. It was in this spirit of accepting only the observable that he regarded atomic and molecular theories with great suspicion.

Berthelot’s publications were particularly numerous. Jungfleisch lists 1,600 titles of papers on inorganic, organic, physical, analytical, technical, agricultural, and physiological chemistry, as well as on the history of chemistry. His work in organic chemistry may, however, be singled out as being of special importance; and if his contributions to physical chemistry hold second place, even they may be considered as originating in the context of his interest in the reactions and formation of organic compounds. In order to systematize Berthelot’s vast work, covering a period of sixty years, Graebe divided his productive life into four periods:

(1) The first organic period, 1850–1860. This covers his work on alcohols and includes his early work on synthesis. In the fall of 1860 he published his definitive work on organic synthesis.

(2) The second organic period, 1861–1869. This period is characterized by research and synthesis of acetylene, benzene, and aromatic compounds occurring in coal tar. It was in the early 1860’s that Berthelot collaborated with Péan de Saint-Gilles on the formation and decomposition of esters, research that constituted a bridge between his interest in organic and physical chemistry. At the end of this period Berthelot was using hydrogen iodide to reduce organic compounds.

(3) The period 1869–1885, which covers Berthelot’s most important contributions to thermo chemistry.

(4) The period 1885–1907, in which Berthelot’s most original work was his contribution to agricultural chemistry and to the history of chemistry.

Berthelot’s first publication, read to the Académie des Sciences on 27 May 1850, was concerned with a simple method of liquefying a gas by applying pressure. The choice of this physical topic may have been inspired by his admiration for Regnault, but in the next year his deep interest in organic chemistry revealed itself. He studied the action of red heat on alcohol and acetic acid. It was already known that at high temperatures alcohol could be transformed into a crystalline solid, naphthalene. Berthelot was able to show that in addition benzene and phenol were formed. Acetic acid at red heat produced naphthalene and benzene. He concluded very significantly that the synthesis (synthèse) of naphthalene, benzene, and possibly phenol, could now be considered as an established fact, since they could all be obtained from acetic acid, which in turn could be prepared via the respective Stages: carbon disulfide, carbon tetrachloride, trichloracetic acid. This was one of the first examples of the use of the word synthesis to denote the production of organic compounds from their elements.²

Two compounds to which Berthelot gave considerable attention were oil of turpentine and camphor. It was known that on reaction with hydrochloric acid, turpentine formed a hydrochloride, C₁₀H₁₆. · HCL. In 1852 Berthelot showed that the reaction could be taken further to produce a product identical with oil of lemon. It was Berthelot who first discovered isomeric changes in oil of turpentine, from which he obtained the solid hydrocarbon camphene. He distinguished what we would now call d-pinene and l-pinene and d-, l-, and dl-camphene. He found that camphene may be oxidized by chromic acid (or by air in the presence of platinum black) into a camphor like substance; in 1870 he proved that the product was true camphor.

The classical work on fats had been carried out by Chevreul. In 1853 and 1854, Berthelot established his reputation in this field by his research on the derivatives of glycerin. By heating glycerin with hydrochloric acid and a selection of fatty acids, he obtained compounds of glycerin with acetic, valeric, benzoic, and sebacic acids. He went on to obtain compounds of glycerin with one, two, or three molecules of acid, the other product being contained in natural fats, e.g., tristearin. Thus, with stearic acid and glycerin he obtained successively monostearin, distearin, and tristearin. He also investigated the products of glycerin with other acids, including acetic acid, the reactions for which he formulated as follows (C = 6, O =8):

Whichever of the above esters was hydrolyzed, the product was glycerin. From these reactions Berthelot concluded that glycerin in organic chemistry corresponded to phosphoric acid in inorganic chemistry as alcohol corresponded to nitric acid. In other words, this was the beginning of the idea that, corresponding to polybasic acids in inorganic chemistry, there were polyatomic alcohols in organic chemistry. Berthelot’s younger contemporary and rival, Adolphe Wurtz, is sometimes given credit for this work, although Wurtz’s contribution in 1855 was to make the correct analogy between different salts of the same (ortho-phosphoric) acid rather than the three different acids of phosphorus to which Berthelot had referred. Berthelot’s most important contribution in his work on glycerin was to introduce the concept (and name) of polyatomic alcohols, but hardly less important was his synthesis of stearin and palmitin, the chief constituents of ordinary hard fats. He also carried out further work on the esterification of glycerin, some of it in collaboration with his pupil S. de Luca.

From glycerin Berthelot turned his attention to sugars and succeeded in isolating several new sugars. He showed that sugars behave partly as polyatomic alcohols (i.e., with the—OH group) and partly as aldehydes (i.e., with the —COH group). With the object of systematizing the confused knowledge of sugars, he divided carbohydrates into three classes: (1) ordinary sugars, which are like either (a) glucose (i.e., monosaccharides) or (b) cane sugar (i.e., polysaccharides); (2) carbohydrates, such as starch, cellulose, etc.; and (3) polysaccharides, which On hydrolysis combine with water to form glucoses:

Berthelot gave cane sugar the systematic name saccharose. From his researches on sugar and alcohol he naturally had an interest in fermentation. He showed that the conversion of cane sugar into invertsugar in fermentation is caused by an enzyme (ferment glucosique) present in yeast. He succeeded in obtaining it from an extract of yeast through precipitation by alcohol. Having obtained new sugars and thrown some light on the relation of sugars to other compounds, Berthelot turned to the alcohols. He prepared new alcohols from cholesterol, ethal, Borneo camphor, etc. He gave a definition of alcohols as neutral compounds consisting of carbon, hydrogen, and oxygen, and which with acids had water eliminated to form another neutral compound. The latter was capable of taking up water to form the original alcohol and acid. He was the first to consider the phenols as a group, which he characterized in a similar way.

One of the earliest of Berthelot’s triumphs in his program of synthesis was in the preparation of alcohol. This was, of course, traditionally the product of fermentation of sugars with yeast; but in 1854 Berthelot showed that it could be prepared from ethylene. When ethylene was subjected to prolonged and vigorous shaking with sulfuric acid, it dissolved; and when the product was heated with water and distilled, the alcohol passed over. An obvious objection to this preparation was that the ethylene had itself been obtained from alcohol. Berthelot therefore obtained ethylene from coal gas as ethylene iodide by passing the crude gas into a solution containing iodine. Hennel had already suggested in 1828 thatethylene could be converted to alcohol by treatment with sulfuric acid but had been criticized by Liebig, so that most chemists in the mid-nineteenth century regarded the possibility of this conversion as doubtful. The fact that previous work had been done on the subject was emphasized by Chevreul in an attack on Berthelot, who had neglected to mention this. By a similar method Berthelot synthesized isopropyl alcohol from propylene.

Berthelot had now begun his program of general synthesis of organic compounds, and in 1856 he set out to prepare formic acid. He reasoned that formic acid was related to carbon monoxide in the same way as alcohol was to ethylene. As he wrote it:

As he had produced alcohol by adding Water to ethylene in the presence of an acid capable of fixing the alcohol, so he should be able to react water with carbon monoxide in the presence of an alkali to fix the acid product. He accordingly heated moist caustic potash in an atmosphere of carbon monoxide for Seventy hours. This produced potassium formate, which, when distilled with sulfuric acid, yielded formic acid in no way different from that occurring naturally in the ant.

Berthelot then synthesized methane (contaminated with a little ethylene) by passing a mixture of carbondisulfide vapor and hydrogen sulfide over red-hotcopper. Then in 1857, by reacting methane with chlorine, he obtained methyl chloride, which, on hydrolysis, formed methyl alcohol. There is an obvious parallel between the success of Cannizzaro two years earlier in obtaining benzyl alcohol from toluenevia benzyl chloride. Berthelot, nevertheless, achieved the first true synthesis of an aliphatic alcohol, and in 1858 he summarized his achievements in a long table, “Sur la synthèse des carbures d’hydrogène,” in which he described his preparation of the hydrocarbons methane, ethylene, propylene, butylene, amylene, ethane, and propane, as well as benzene and naphthalene. The first stage in synthesis, the preparation of these hydrocarbons and their conversion to the corresponding alcohol, was the most difficult stage; but once the alcohol had been prepared, it was possible “to achieve the synthesis of an almost infinite number of organic compounds.” Berthelot attacked the idea of a vital force distinguishing organic from inorganic compounds. Chemistry had proceeded upto then by the method of analysis, but by the complementary method of synthesis he claimed to have shown that the forces acting in organic chemistry were no different from those operating in inorganic compounds.

In Berthelot’s memoir of 1858 he wrote that “carbon does not combine directly with hydrogen.” Before he achieved this he wrote his monumental Chimie organique fondée sur la synthèse, in which he presented a review of his work in organic chemistry during the previous ten years. The work begins with an extensive historical introduction, which contains no more than a passing reference to Wöhler’s preparation of urea in 1828. One obtains the impression from the book that the author was the first to recognize the importance of synthesis in organic chemistry and that it was he who had undertaken the basic research. The first volume is devoted to a discussion of the synthesis of hydrocarbons and the synthesis of alcohols. In the second volume glycerin and sugars are discussed, and toward the end there is a chapter dealing with the evidence for genuine synthesis and the implications for physiological chemistry. Berthelot emphasized throughout the work that the success of synthesis in organic chemistry meant that the claim of vitalists that vegetable and animal substances were essentially different from those made in the laboratory was no longer tenable. There were not two chemistries but one, and chemical reactions in both the inorganic and organic realms depended ultimately on purely mechanical factors. In his conclusion Berthelot argued that chemistry differed from a descriptive science such as natural history by being creative and that in this it resembled the mathematical sciences.

Acetylene was first prepared in 1836 by Edmund Davy, for whom it was “a new carburet of hydrogen.” The gas was then forgotten until it was rediscovered by Berthelot in 1860. Berthelot prepared it by passing either ethylene, or methyl or ethyl alcohol in the vapor state, or ether through a red-hot tube. Alternatively it could be prepared by passing an electric discharge through a mixture of cyanogen and hydrogen. To isolate it he made use of its reaction with ammoniacal cuprous chloride solution to form cuprous acetylide, a substance discovered by Quet in 1858. Berthelot gave the gas the name “acetylene,” saying that it was derived from acetyl (C₂H₃—H) in the same way that ethylene was related to ethyl (C₂H₅—H). Having already found that acetylene is the product formed when ethylene or methane is strongly heated or sparked, Berthelot concluded that it is the most stable of hydrocarbons and might therefore be produced by direct combination of carbon and hydrogen. Taking special precautions to ensure the purity of his materials, he therefore passed hydrogen through an electric arc formed between carbon poles. By reduction of acetylene Berthelot obtained ethylene and, ethane and by oxidation, acetic acid and oxalic acid, all reactions of great use to their author in extending his program of synthesis. As the direct reaction of acetylene with chlorine usually produced an explosion, Berthelot and Jungfleisch used antimony chloride (as a negative catalyst) and succeeded in obtaining two addition products.

Berthelot opened a new field when he carried out a systematic investigation of hydrocarbons obtained by heating suitable substances in the temperature range from red to white heat. His most famous experiment was that in which he heated acetylene in a glass tube; polymerization took place, forming benzene with some toluene. This was the first demonstration that it was possible to effect a simple conversion of an aliphatic to an aromatic compound. By passing benzene vapor through a red-hot iron tube filled with broken glass, Berthelot obtained diphenyl. Similarly, he obtained styrolene and naphthalene from benzene and acetylene, and acenaphthene from naphthalene and ethylene. These reactions had the additional value of throwing light on the formation of by-products in the manufacture of coal gas. For example, Berthelot first discovered acenaphthene (C₁₀H₆. · C₂H₄) as described above and then as a constituent of coal tar. He also discovered fluorene (C₁₃H₁₀) in crude anthracene and heavy coal-tar oil.

After Berthelot’s success in obtaining acetylene directly from carbon and hydrogen, he considered acetylene to be the most important starting point in his whole system of synthesis, since from it could be obtained ethylene, methane, and benzene:

Previously Berthelot had deliberately used molecular formulas only, but from 1864, when he gave a lecture on isomerism to the Société Chimique in Paris, he began to develop the molecular implications of his researches. Nevertheless, he remained outside the development of the theory of chemical structure developed by Butlerov and Kekulé and the notational reforms arising from the Karlsruhe Congress of 1860, so that he continued to use the old equivalent notation. He distinguished hydrocarbons according to their degree of saturation, as follows (using modern atomic weights):

According to this system, and wishing to call attention to its method of synthesis, Berthelot considered benzene an incomplete hydrocarbon of the fourth order. This formulation was acceptable for its reduction to hexane but was unsatisfactory in accounting for the majority of benzene’s reactions, where it behaves as a saturated hydrocarbon. Berthelot rejected Kekulé’s formula for benzene (1865–1866), and it was not until 1897 that he accepted modern structural formulas.

Berthelot’s last major research in organic chemistry was the application of hydrogen iodide as a reducing agent—he called it “une méthode universelle d’hydrogenation.” His publications on this research covered the period 1867–1870. Although he claimed that they were a continuation of work published in 1855, it must be mentioned that meanwhile Lautemann had already used hydrogen iodide as a reducing agent in organic chemistry. Berthelot, anxious to carry out even the most difficult reductions, was prepared to use concentrated hydriodic acid saturated at 0°C and heated with the substance to be reduced in an oil bath up to 280°C. He succeeded in reducing a large number of unsaturated aliphatic hydrocarbons. His results with aromatic hydrocarbons were less definite. His study of the mechanism of decomposition of hydrogen iodide provides a further link with his work in physical chemistry.

One of the earliest papers in which Berthelot revealed his interest in physical chemistry was published in 1856. In this he paid special attention to the boiling point, specific gravity, specific heat, heat of combustion, and refractive index of organic compounds, particularly esters. His great contributions to physical chemistry began in the 1860’s. Berthelot later explained how he had become interested in physical chemistry:

In a succession of publications for several years I endeavored to compare experimentally the origins of organic compounds with those of inorganic compounds and to formulate general methods of synthesis. To extend my research I considered it appropriate to make a special study of the mechanism of these changes. The experiments which I have published on the laws governing the production of esters were published with this intention. Now I propose to examine what thermal phenomena accompany the formation and the decomposition of organic compounds—in other words the extent of the energy change [le travail des forces vives] necessary to bring about their synthesis.³

Thus Berthelot’s contributions to physical chemistry arose directly from his consuming interest in the synthesis of organic compounds. His studies on chemical equilibrium published in 1862 and 1863 were followed by equally fundamental work on thermochemistry.

Berthelot and L. Péan de Saint-Gilles studied the reaction of alcohols with acids to form the corresponding ester and water. They found that the reaction never went to completion but arrived at an equilibrium state that was independent of the quantities (measured in equivalents) of alcohol, acid, ester, or water present at the beginning. On the other hand, the rate of reaction did depend on the quantities of alcohol and acid present: “The amount of ester produced at each moment is proportional to the product of the active masses [masses actives] present.” ⁴ Such a statement appears to be an anticipation of the law of mass action later formulated by Guldberg and Waage. Berthelot attempted a mathematical treatment and drew graphs illustrating the formation and decomposition of esters. Berthelot and Saint-Gilles, however, while appreciating that the equilibrium was affected by the reverse reaction (ester + water), failed to take this into consideration in deriving a general mathematical expression. In their comprehensive experiments they varied temperature, pressure, concentration, and types of alcohols and acids used. They recorded the increase in reaction velocity with rise of temperature, although the final position of equilibrium was found to be almost independent of temperature. As one of their experiments on the effect of mass, one equivalent of ethyl alcohol was reacted with increasing amounts of acetic acid and the various yields of ester formed were recorded. With one equivalent of acid reacting with x equivalents of alcohol the amount of ester formed was also recorded:

During their investigation of a large number of alcohols Berthelot and Saint-Gilles found that the rate of reaction of borneol with acids was excessively slow, but it was left to Menschutkin to clear up the relation between the constitution of an alcohol and its rate of esterification. When Guldberg and Waage announced their law of mass action, they fully acknowledged their debt to the studies of esterification by Berthelotand Saint-Gilles.

In 1856, in the course of his investigations of esters, Berthelot established that the heat of combustion of an ester is almost exactly equal to the sum of the heats of combustion of the alcohol and acid from which it is formed. In this, as in some later work, he was able to make use of the experimental results of Favre and Silbermann. It was not until 1865, however, that Berthelot seriously turned his attention to problems of thermochemistry. He chose this subject for his lectures at the Collège de France, but he made it clear from the beginning that his interest was really in the heat changes involved in the formation and decomposition of organic compounds so that these could be compared with the comParatively well-known basic thermochemistry of inorganic chemistry as a further basis of comparison between the two branches of the science. It was in these lectures that Berthelot introduced the terms exothermic and endothermic.

Berthelot enunciated the principle that the heat evolved or absorbed in a chemical change depends only on the initial and final states of the reactants and products, provided no external work is done. This is Berthelot’s “second principle,” analogous to Hess’s law of constant heat summation. He based this principle on the assumption of an equivalence between internal work (Ie travail moléculaire) and heat changes in a chemical reaction (Berthelot’s “first principle”). Best known is Berthelot’s “third principle,” or “law maximum work,” which was first published in its complete form in 1873: “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.” In the same publication Berthelot introduced the expression “principle of maximum work.” The honor of beginning a new epoch in thermochemistry must be shared between Berthelot and Julius Thomsen, who had arrived in 1853 at essentially the same principle as that established by Berthelot in 1873. The principle was soon recognized as no more than a useful approximation, strictly true only at a temperature of absolute Zero; it was superseded by the researches of Helmholtz, Gibbs, and van’t Hoff. The accuracy of Berthelot thermochemical data has often been Criticized, but sometimes it was his arithmetic rather than his experimental work that was at fault. In interpreting nineteenth-century thermochemical data it is also necessary to know that Berthelot’s calories refer to water at 0° C., whereas Thomsen, for example, used the range 18°C. -20°C.

Berthelot tried to improve the experimental technique of thermochemistry. Recognizing the unreliability of the mercury calorimeter used by Favre and Silbermann, for example, he used a water calorimeter and either a platinum reaction chamber or one made of glass to facilitate direct observation. By the use of a water jacket, a mechanical stirrer, and a thermometer reading to .005°C., he was able to carry out experiments accurately over small temperature ranges. After more than ten years’ research on thermochemistry, Berthelot published a major two-volume work for which he significantly chose the title Essai de mécanique chimique fondée sur la thermochimie. In the first volume, entitled Calorimétrie, Berthelot gave a general survey of thermochemistry, with particular reference to his own apparatus and results. The second volume, entitled Mécanique, was a general account of chemical reactions and decompositions. Berthelot continued his thermochemical research by determining the heats of combustion of gases. He introduced the use of the bomb calorimeter, in which the gas under test was mixed with excess oxygen compressed to 20–25 atmospheres and then sparked. This method enabled him to determine heats of combustion with an accuracy hitherto unattainable. With his bomb calorimeter, Berthelot made a fundamental contribution to both pure and applied chemistry. This was immediately recognized, and a stream of foreign scientists came to Paris to acquire firsthand knowledge from Berthelot of the new thermochemical methods. Through Berthelot, his pupils, and such collaborators as Vieille and Recoura, there was established a substantial body of reliable data of heats of combustion, solution, neutralization, and so on. Berthelot’s continuing interest in thermochemistry is suggested by the publication in 1897, when he was seventy years old, of another two-volume work, Thermochimie. Données et lois’ numériques. He had already devoted to practical methods the smaller work Traité pratique de calorimétrie chimique (1893).

Almost as important was the fundamental work carried out by Berthelot, largely in collaboration with Jungfleisch, and published in the years 1869 and 1872. Studying the distribution of a solute between two immiscible solvents (e.g., water and benzene) or partially miscible solvents (e.g., water and ether), they were able to enunciate the partition law: At a given temperature the quantities of solute dissolved by equal volumes of two solvents is a constant.” They called this constant the partition coefficient (coefficientde partage). Some twenty years later Nernst investigated some apparent exceptions to this law.

While serving as president of the scientific commission appointed to bring any possible aid from science to help in the defense of Paris during the Franco-Prussian War, Berthelot investigated the possibility within the city of extracting saltpeter for gunpowder. Also in November 1870 he presented to the Académie des Sciences three memoirs on explosives, which were published in full in the Comptes rendus under the heading “Art militaire.” Combining his patriotic duty as a Frenchman and his interest in thermochemistry, Berthelot showed how the power of explosive materials could be quantitatively expressed. He expanded this research in his book Sur la force des matières explosives d’après la thermochimie, first published in 1871 but greatly expanded in the two-volume definitive work published as a third edition in 1883. In the intervening period Berthelot had made a particular study of the thermochemistry of nitrogen compounds used as the basis of explosives. But it was his work carried out in collaboration with Vieille that laid the foundations of a new scientific study of the mechanism of explosions. They found that explosions were propagated in a manner in many ways analogous to that of a sound wave. They accordingly introduced the concept of an explosive wave (onde explosive), found to have a velocity much greater than that of sound; for example, with an explosive mixture of hydrogen and oxygen the velocity was 2,841 meters per second. The explosive wave was propagated uniformly. Its velocity depended on the nature of the explosive rather than on the material or dimensions of the vessel. Apart from its direct utility, Berthelot found his research on explosives interesting because in it he witnessed natural forces acting under extreme conditions. He insisted that his studies of explosives could have peaceful uses; and in 1896, after accidents with liquid acetylene used for illumination, he and Vieille collaborated in a study to establish how acetylene could be used with safety.

The possibility of finding new reactions by using a silent electric discharge also appealed to Berthelot. He constructed an ozonizer, essentially the same as that devised earlier by Brodie. By passing a silent electric discharge for up to ten hours through a mixture of sulfur dioxide and oxygen, Berthelot discovered persulfuric anhydride, S²O⁷. This is the anhydride of an acid of both theoretical and practical importance for the use of its salts as oxidizing agents. It was Berthelot’s lifelong interest in energy states that prompted his studies of allotropic forms of sulfur, phosphorus, and arsenic, and his discovery in 1891 (simultaneously with Mond and Quincke) of iron carbonyl.

Berthelot’s first study of animal heat was in 1865, and in this he followed the thermal tradition of Lavoisier and Laplace. In 1890 he took up the subject again, carefully distinguishing the heat produced in the lungs by the action of oxygen in the blood from the later reaction in which carbon dioxide is produced, and he was able to show that the former reaction produced only one-seventh of the total heat.

In other experiments Berthelot was able to show that the combustion of foodstuffs in the laboratory produced no less heat than in the body. There was therefore no energy to relate to any vital force, a conclusion in which Berthelot took particular satisfaction. He opposed Pasteur’s vitalistic interpretation of fermentation, preferring a theory of fermentation fully analogous to that of inorganic catalysts, thus once more championing the view of the strict parallel between the organic and the inorganic.

In 1883 Berthelot founded a research establishment for vegetable chemistry, and during the last twenty-five years of his life he undertook research into aspects of chemistry useful to agriculture. He found that certain carbohydrates, such as cellulose, could be made to absorb nitrogen under the action of a silent electric discharge. By treating them with lime, the absorbed nitrogen was liberated as ammonia. He was able to demonstrate that the fixation of atmospheric nitrogen by sparking is parallel to the natural process in plants. In 1885 he made his first reference to microorganisms capable of fixing nitrogen and in 1893, in collaboration with Guignard, he succeeded in isolating and forming a culture of such bacteria. In accordance with his usual practice, he brought together work done by himself and his collaborators (particularly G. André) and published it in book form. The result was his Chimie végétale et agricole (1899). Berthelot’s last chemical book, Traité pratique de l’analyse des gaz (1906), concerned a subject he had studied practically from the time of his early syntheses of hydrocarbons.

NOTES

1. The spelling “Marcelin” was used on his birth certificate, and Berthelot himself sometimes Wrote it that way, particularly toward the end of his life in the signing of official documents.

2. In 1850 Williamson had described the production of ethyl methyl ether from sodium ethoxide and methyl iodide as a “synthesis,” Philosophical Magazine, 3rd ser., 37 (1850), 350.

3.Annales de chimie et de physique, 4th ser., 6 (1865), 290–291.

4. Ibid 3rd ser., 66 (1862), 112.

BIBLIOGRAPHY

I. Original Works. Berthelot wrote the following books (all published in Paris): Chimie organique fondée sur la synthèse, 2 vols. (1860); De la synthèse en chimie organique. Leçon professée le 16 Mars 1860 à la Sociéié chimique de Paris (1861); Sur les principes sucrés. Leçons professées à la Société chimique de Paris (1863); Leçons sur les méthodes générales de synthése en chimie organique, professées au Collège de France (1864; 1876; 1879: 1880; 1883; 1887; 1891; 1897; 1903; 1910); Sur l’isomérie. Leçons de chimie professées devant la société chimique de Paris (1866); Sur la force de la poudre et des matiéres explosives (1871; 2nd ed. 1872; see also Sur la force…, 1883): Traité élémentaire de chimie organique (1872: later eds. with Jungfleisch, 2 vols., 1881, 1886, 1898 [Vol. I]; 1904 [Vol II]: new ed. of Vol. I, 1908); Essai de mécanique chimique fondée sur la thermochimie, 2 vols. (1879; supp., 1881); Sur la force des mattéres explosives d’après la thermochimie, 3rd ed., 2 vols. (1883); Les origines de l’alchimie (1885) Science et philosophie (1886; 1905); Collection des anciens alchimistes Grecs, 3 vols. (1887–1888); Introduction à l’étude de la chimie des anciens et du moyen age (1889); La révolution chimique, Lavoisier (1890; 2nd ed., 1902); Histoire des sciences. La chimie au moyen age, 3 vols. (1893); Traité pratique de calorimétrie chimique (1893; 2nd ed., 1905); Science et morale (1897); Thermochimie. Données et lois numériques, 2 vols, (1897); Chaleur animale. Principes chimiques de la production de la chaleur chez les êtres vivants, 2 vols. (1899); Chimie végétale et agricole. Station de chimie végétale de Meudon, 4 vols. (1899); Les carbures d’hytirogène, 1851–1901. Recherches expérimentales, 3 vols. (1901); Science et éducation (1901); Science et libre pensée (1905); Archélogie et histoire des sciences (1906); Trailé pratique de l’analyse des gaz (1906).

A selection from Berthelot’s principal research papers is listed below. The order follows that of the text. “Sur un procédé simple et sans danger pour démontrer la liquéfaction des gaz et celie de I’acide carbonique en particulier,” in Comptes rendus, 30 (1850), 666–667; “Action de In chaleur rouge Stir I’alcool et sur l’acide acétique,” in Annales de chimie et de physique, 33 (1851), 295–302: “Sur le bichlorbydrate d’essence de térébenthine,” in Comples rendus, 35 (1852), 136–738; “Sur les diverses sortes d’essence de térébenthine,” ibid., 36 (1853), 425–429 (see also Annales, 38 [1853], 38; 39 [1853], 5; 40 [1854], 5); “Sur la série camphénique,” in Comptes rendus, 47 (1858), 266–268; “Sur l’oxidation des carbures d’hydrogène,” in Annales, 19 (1870), 427–429; “Sur les combinaisons de la glycérine avec les acides,” in Comptes rendus, 36 (1853), 27–29: ‘Mémoire sur les combinaisons de la glycérine avec les acides et sur la synthèse des principes immédiats des graisses des animaux,” in Annales, 41 (1854), 216–319, esp. 296; “Sur quelques matières sucrées,” ibid., 46 (1856); 66–89; “Sur divers carbures contenus dans le goudron de houille,” ibid., 12 (1867), 195–243; “Sur plusicurs alcools nouveaux. Combinaisons des acides avec la cholesterine, l’éthal, le camphre de Bornéo et la méconine,” ibid., 56 (1859), 51–98; “Sur la reproduction de l’alcool par le bicarbure d’hydrogène,” in Comptes rendus, 40 (1855), 102–106; “Transformation de l’oxyde de carbone en acide formique,” ibid., 41 (1855); 955; “Synthèse des carbures d’hydrogène,” ibid., 43 (]856), 236–238; “Synthèse de l’esprit-do-bois,” ibid., 45 (1857), 916–920; “Sur la synthèsedes carbures d’hydrogène,” in Annales, 53 (1858). 69–208; “Note sur une nouvelle séne de composés organiques, le quadricarbure d’hydrogène et ses dérivés,” in Comptesrendus, 50 (1860), 805–808; “Recherches sur l’acétylène,” in Annales, 67 (1863), 52–77, esp. 65–68; “Nouvelle méthode pour la synthèse de l’acide oxalique et des acides homologues.” in Comptes rendus, 64 (1867), 35–38; “Les polymères de l’acétylène. Première partie: Synthèse de la benzine,” ibid., 63 (1866), 479–484; “Action de la chaleur sur quelques carbures d’hydrogéne,” in Annales, 9 (1866), 445–469, esp. 454; “Action reciproque des carbures d’hydrogéne. Synthése du styrolene, de la naphtaline, de l’anthracène,” ibid., 12 (1867), 5–52; “Sur divers carbures contenus dans le goudron de houille,” ibid., 195–243; “Méthode universelle pour réduire et saturer d’hydrogèneles composés organiques,” in Comptes rendus, 64 (1867), 710–715, 760–764, 786–791, 829–832; “Remarques sur quelques propriétés physiques des corps conjugués,” in Annales, 48 (1856), 332–347; “Recherches sur les affinités:—De la formation et de la décomposition des éthers,” ibid., 65 (1862), 385–422; 66 , 5–110; 68 (1863), 225–359, esp. 290–291, written with Péan de St. Gilles; “Recherches de thermochimie. Premier mémoire. Sur la chaleur dégagée dans les réactions chimiques,” ibid., 6 (1865), 290–328; “Sur la statique des dissolutions salines,” in Comptes rendus, 76 (1873). 94–98; “Méthode pour mesurer la chaleur de combustion des gaz par detonation.” in Annales, 23 (1881), 160–187; “Nouvelle méthode pour la mesure de la chaleur de combustion du charbon et des composés organiques,” in Comptes rendus, 99 (1884), 1097–1103, written with Vieille; “Sur les lois qui président au partage d’un corps entre deux dissolvants (expériences),” ibid ., 69 (1869), 338–342, written with Jungfleisch; “L’onde explosive,” in Annales, 28 (1881), 289–332, written with Vieille; “Sur l’acide persulfurique, nouvel acide oxygéné du soufre,” in Comptes rendus, 86 (1878), 20–26; “Sur la chaleur animale, chaleur dégagée par l’action de l’oxygènesur le sang,” in Annales, 20 (1890); 117–202, esp. 199; “Fixation directe de l’azote atmosphérique libre par certains terrains argileux,” in Comptes rendus, 101 (1885), 775–184; “Nouvelles recherches sur les microorganismes fixateurs de l’azote,” in Annales, 30 (1893), 419–431.

II. Secondary Literature. The following studies describe Berthelot’s life and work. The articles by Graebe and Jungtleisch are particularly thorough, H. E. Armstrong. “Marcelin Berthelot and Synthetic Chemistry,” in Journal of the Royal Society of Arts, 76 (1927–1928), 145–171; A. A. Ashdown, “Marcellin Berthelot,” in Journal of Chemical Education, 4 (1921), 1217–1232; G. Bredig, “Marcelin Berthelot,” in Zeitschrift für angewandete Chemie, 20 , pt. 1 (1907), 689–694: A. Boutaric, Marcellin Berthelot (Paris, 1927); E. Farber, “Berthelot,” in Das Buch der grossen Chemiker, G. Bugge, ed., II (Berlin, 1930), 190–199, trans. in E. Farber, ed., Great Chemists (1961), pp. 677–685; C. Graebe, “Marcelin Berthelot:’ in Berichte der Deutschen Chemischen Gesellschaft, 41 (1908), IIIB. 4805–4872; E. Jungfleisch. “Notice sur la vie et les travaux de Marcellin Berthelot,” in Bulletin de la Société chimique de France, 13 (1913), i–cclx; L. Velluz, Vie de Berthelot (Paris, 1964); and R. Virtanen, Marcelin Berthelot. A Study of a Scientist’s Public Role, University of Nebraska Studies, no. 31 (Lincoln, 1965).

M. P. Crosland