WORKS AND ACTIVITIES OF MARCELLIN BERTHELOT1

Camille Matignon, Paris.

MARCELLIN BERTHELOT (1827—1907)

Among the names of the greatest representatives of humanity that illuminate the nineteenth century, the name of the chemist who created organic synthesis and established the laws of thermochemistry shines with a quite special brilliance. The works of M. Berthelot2 are extensive and brilliant. The result of his activity was about 1,500 memoirs, of which the first was printed in May 1850 in the Annales de Chimie et de Physique and concerned his work carried out in Pelouze’s chemical school, while the last was presented to the Academy of Sciences in the very month in which Berthelot died—namely, in March 1907.

All, or almost all, of his investigations concern four questions: the synthetic preparation of complex organic substances, the study of the forces that are connected with the combination and decomposition of chemical substances, then agriculture and the history of chemistry. We shall try briefly to set forth the most essential points, without going into the details of these works, and outlin—

drawing with rough general lines these beautiful creations, among the most remarkable productions of the human mind¹).

TWO CHEMICAL REVOLUTIONS.

In 1889, precisely in the year of the centenary of the French Revolution, Berthelot assumed the duties of permanent secretary of the Academy of Sciences and delivered, at a public meeting of the Academy, an address devoted to Lavoisier. With documents in hand, and in an exposition extraordinarily profound in thought, he showed the nature and character of the fundamental reform carried out by Lavoisier in the field of chemical theories at the end of the eighteenth century.

The law of the conservation of matter and Lavoisier. Berthelot clarified the significance of the principal discovery of the “founder of modern chemistry,” the discovery from which all his subsequent work follows and which consists in a clear understanding of the difference between ponderable bodies and imponderable agents, which can influence ponderable bodies without changing their weight. The creator of the true chemical method, Lavoisier, formulated the concept of a simple body and proved that the composition of a substance must be determined with complete precision by analysis and synthesis. Having proclaimed his principle of the conservation of matter in the course of chemical reactions, he created a genuine chemical revolution, the theoretical and practical consequences of which were of such great importance that it is impossible even to imagine them²). Marcellin Berthelot, who noted

¹) See “Notice sur la vie et les travaux de Marcelin Berthelot” by Émile Jungfleisch, Bull. Soc. Chim. France. 5 February 1913. Address delivered at the unveiling of the monument to Marcelin Berthelot. French Institute, 1917.

²) In an excellent report at the Academy of Sciences in Paris (summer 1927), on the occasion of the presentation of the work by P. P. Lazarev, “Aperçu historique du développement des sciences exactes en Russie,” C. Matignon pointed out to French chemists a fact hitherto unknown to them: that the law of conservation of mass had been discovered both theoretically and experimentally several decades before Lavoisier by Lomonosov. It is curious that even so great a chemist as D. I. Mendeleev, who knew the history of science deeply, did not note this fact (see Principles of Chemistry, first edition). P. L.

revolutionary character of Lavoisier’s works, himself produced a revolution in chemistry by creating, in the period from 1854 to 1867, organic synthesis; just like Lavoisier, he gave science and technology incalculable riches.

Chemical synthesis and Berthelot. Before Berthelot’s work, scholarly opinion accepted a fundamental distinction between organic and mineral chemistry. For the production of organic substances within living organisms, the indispensable action of a vital force was admitted. In 1842 Charles Gerhardt said: “The chemist does exactly the opposite of what living nature does; he burns, destroys, acts by analysis; only the vital force acts by synthesis; it restores what has been destroyed by chemical forces.” In Berthelot’s work, which appeared in 1843, the assertion of a complete difference between mineral and organic chemistry was likewise clearly formulated. “If it were possible,” said the famous scholar, “to find the cause of this difference, one might obtain the key to the theory of organic chemistry; but this theory is so complex and inaccessible that we cannot hope for its creation, at least at the present time.”

In the same work, after saying a few words concerning the synthesis of urea carried out by Wöhler, Berthelot wrote: “Even in the event that, in time, we are able to obtain from inorganic substances certain compounds of composition analogous to organic substances, this incomplete imitation will be too limited for us to hope to obtain organic bodies as we succeed, in most cases, in doing for inorganic bodies, confirming the analysis of these bodies by their synthesis.” Wurtz in 1850 was less decisive; one may even say that he regarded with a certain optimism the possibility of chemical synthesis in this field. “If,” he said, “by means of reactions consisting in the substitution of hydrocarbon radicals in place of hydrogen, it should someday be possible to build up organic molecules with the same ease with which at present some of them can be decomposed, then this creation of artificial organic substances, from the point of view

theory, will have to place science on a higher level, and this will at once lead to the greatest applications.”

We stand on the threshold of the second chemical revolution. Berthelot, in a letter written in his youth to Renan, spoke of his belief in the unity of the universe, in the unity of its phenomena and its laws. He could not imagine any distinction between the living world and the mineral world, and it may be asserted that his guiding idea in the synthesis of organic substances had a very remote origin. In 1851, when he was only 24 years old, studying the decomposition of alcohol and acetic acid by means of heating, he established the formation of benzene, naphthalene, phenol, and other substances contained in the products of the distillation of mineral oils or fatty oils. He noted that the synthesis of these substances should be regarded as an already accomplished fact, since they could be obtained by means of acetic acid, which had earlier been prepared synthetically by Kolbe. Wöhler, with his synthesis of urea in 1828, and Kolbe, with his synthesis of acetic acid in 1825, were in fact Berthelot’s predecessors, but their works remained isolated, and their theoretical significance was not clarified. The facts they discovered were regarded as separate cases, constituting an exception to the doctrine—then considered almost irrefutable—of the absolute difference between the phenomena of mineral chemistry and the chemistry of the substances of the living organism.

A complete change, an entire revolution, was brought about by Berthelot’s works. At first he carried out the partial synthesis of natural fats by means of fatty acids and glycerin; then there followed a “decisive series of experiments,” as Charles Moureu calls it: the syntheses of allyl isosulphocyanate, or mustard oil (1854), and of ethyl alcohol (1855), formic acid (1855), methyl alcohol (1857), acetylene (1862), and benzene (1867).

One of these discoveries must attract our special attention, since it aroused a general and profound interest in organic synthesis.

Two elements are taken in the free state: hydrogen and carbon. Applying the voltaic arc, Berthelot combines them into a molecule of acetylene. This substance then, by hydrogenation, then by condensation, by the addition of oxygen or carbon, yields, according to the circumstances, either hydrocarbons (ethylene, formene, benzene), or acids (acetic, oxalic, hydrocyanic); and from that moment, from the moment of Berthelot’s synthesis, all the paths of organic chemistry appeared more or less open. Biological phenomena could thus be reproduced in the laboratory; moreover, it could be foreseen that combinations not existing in nature might be created, as Berthelot himself noted. “The domain in which chemical synthesis will one day manifest its creative power is more extensive than the domain of nature as it actually exists.”

This assertion, full of boldness, was bound to have extraordinary consequences. Without doubt, at the moment when Berthelot’s first experimental results were published, it appeared only in a hidden form. Nevertheless, it was bound to lead to works that advanced organic synthesis to the possible limits of perfection which it has attained in our day, creating an important field in the technology of medicines, perfumes, and synthetic dyes.

Thermochemistry.

The establishment of the first general methods for the synthesis of organic substances and their connection with the doctrine of the physico-chemical unity of the phenomena of the living world and the mineral world inevitably led Marcellin Berthelot to the study of the mechanism of chemical reaction. When Berthelot carried out the synthesis of formic acid (1855), combining the elements of water and carbon monoxide, he drew attention to the extreme slowness with which this simple but interesting reaction proceeds. In 1864, studying the already observed facts, he saw that the heat of combustion of formic acid was greater than the heat of combustion of carbon monoxide, which was the starting product for it. Hence the conclusion: in the synthesis of formic ...

acids, heat is absorbed. This reaction is an endothermic reaction, in contrast to exothermic reactions, which liberate heat. Hence there arises the conception of chemical affinity, which Berthelot regards not as some indeterminate force, but as a quantity that can be measured by investigating the absorption or release of heat.

Calorimetry. Calorimetry was splendidly developed thanks to the work of Lavoisier and Laplace, Favre and Silbermann, Thomson and Regnault. Berthelot enriched it with an enormous number of his theoretical discoveries, an enormous number of experimental determinations and numerical data. In the field of calorimetry he created new, precise, and simple methods, well suited to laboratory chemical work and allowing the use of the calorimetric bomb that bears Berthelot’s name. The number of determinations carried out by Berthelot, his collaborators, and his pupils for the thermochemical study of reactions is enormous. All these data, subsequently collected by Berthelot, beginning in 1865, relate to all kinds of reactions and transformations. They enabled Berthelot, also relying on the work of foreign scientists, to formulate three laws that give the measure of the molecular work performed during the course of a chemical transformation and that govern these transformations. These works are of interest for pure science; their role is no less great in application to physiology, agriculture, military affairs, metallurgy, and the electrical industry. They increased our knowledge of the composition of bodies and made the characterization of chemical phenomena more precise.

Berthelot’s three principles. Berthelot established the following three principles of thermochemistry:

1) The principle of molecular work, according to which the amount of heat released in a chemical reaction measures the sum of the chemical and physical work performed during that reaction.

2) The principle of the initial and final states, which is expressed thus: if a system of simple or comp—

WORKS AND ACTIVITY OF MARCELLIN BERTHELOT

of bodies, taken under definite conditions, undergoes physical or chemical transformations capable of bringing it into a new state, and no external mechanical effect is observed in the system, then the quantity of heat evolved or absorbed owing to these transformations depends only on the initial and final states of the system; the thermal effect remains the same, whatever the nature and order of the intermediate states may be.

3) Principle of maximum work: every chemical transformation occurring without the mediation of external energy, at constant temperature, tends to create such a system of substances as evolves the greatest quantity of heat. This third principle is of quite special significance, since it makes it possible to predict the direction in which chemical reactions must proceed. This principle is not an absolute law, but a law with a limited field of application—an extremely general and very valuable empirical rule (Armand Gautier).

The principle of greatest work, which ought rather to be called the principle of greatest heat, attains complete exactness if one separates from the heat of chemical reaction the heat dependent on a change of physical state. At absolute zero maximum work is strictly equivalent to heat of reaction, and one and the same reaction would exist at any temperature if the heats of reaction remained unchanged, which is approximately true for solids, for which there is an almost complete equality of specific heats in different states.

At ordinary temperature Berthelot’s principle applies almost rigorously to the case of reactions between solid bodies.

Nernst regards this principle as a consequence of Carnot’s principle of the dissipation of energy. Exothermic reactions are most numerous at moderate temperatures, when there are neither false nor true equilibria; this applies to the case most common in practice, when it is easy to obtain the corresponding temperatures.

CAMILLE MATIGNON

Research on explosive substances. Berthelot used the principle of thermochemistry in his investigations of explosive substances. Beginning in 1871, he set himself the problem of the strength of powders and explosive substances, noting that to determine the strength of explosive substances four quantities are necessary: 1) the chemical composition of the explosive substance; 2) the composition of the explosion products; 3) the volume of the gases produced; 4) the amount of heat released in the reaction.

This last quantity, he said, measures the maximum work that can be produced by an explosive substance, whereas the initial pressure depends on the volume of the gases obtained in the explosion and on their temperature.

Proceeding from these new points of view, Berthelot made a major contribution to the study of the phenomena of decomposition of powders and explosive substances. In this investigation Vieille found the first data that led him to the discovery of smokeless powder. Together with Vieille, Berthelot came to the admissibility of recognizing a special wave-like motion, characteristic of the transmission of explosive reactions—the explosive wave.

The action of this motion may be compared with the action of a sound wave, with, however, the fundamental difference that the sound wave is transmitted from layer to layer with little living force, with a small change in pressure, and with a definite velocity depending only on the physical composition of the vibrating medium, whereas the change in chemical composition, propagating together with the explosive wave, gives the latter enormous living force and an enormous excess of pressure1.

Animal heat. The study of the development of heat in living beings constitutes a chapter of thermochemistry of enormous importance for physiologists and animal husbandry specialists. The first data concerning animal heat were obtained by Lavoisier, who regarded the origin of this heat as the result of the combustion of carbon in the oxygen inhaled by the animal.

The quantity of heat, according to Dulong (in 1820), must be proportional not to the weight of the oxygen absorbed, but to the weight of the carbon dioxide and water formed.

Berthelot showed that measurements of the quantities of oxygen absorbed and of carbon dioxide and water obtained do not make it possible to calculate the phenomenon of heat production with sufficient accuracy. The method of thermochemical determination made it possible to elucidate and distinguish the generation of heat depending on complete and incomplete direct or indirect oxidations, on reactions of hydration, hydrolysis, polymerization, and synthesis. The production of heat by living beings thus proved, in reality, to be more complex. The transformations of the chemical substances that constitute food occur according to the very same physico-chemical laws in the organism and in laboratory apparatus: the amount of energy that is liberated in the process is always one and the same, whatever the intermediate states may be through which these substances have passed in order to go from their initial state to the final state; the maintenance of life requires no energy of any kind that would be characteristic of the phenomena of life.

Agronomical Chemistry

The development of general methods of organic synthesis led Berthelot to the study of the synthesis of nitrogenous substances through the fixation of nitrogen by substances, and subsequently to work on the assimilation of nitrogen by plants.

Before Berthelot’s work, this subject had given rise to numerous disputes among chemist-agronomists.

In 1876 Berthelot discovered that pure nitrogen, or nitrogen taken from the air, is absorbed by organic substances at ordinary temperature under the influence of electrical discharges, yielding nitrogenous compounds belonging to humic substances. When, in 1883, an agronomical-chemistry station, located on land belonging to the old château at Meudon, was attached to the laboratory of organic chemistry of the Collège de France, Berthelot again took up the study of this question.

He confirmed his initial observations and in 1890 obtained the absorption of nitrogen by plants enclosed in a closed vessel in an electric field, under conditions analogous to those found in nature.

Seeking to deepen the reaction of nitrogen fixation under the influence of electric effluvia, Berthelot discovered in 1885 new and far more general conditions for the direct utilization of nitrogen: “the action of clay soils and of the organisms enclosed in them.”

This discovery was destined to lead to important consequences, which appeared in Hellriegel’s works in 1886: among these are the discovery of the role of the nodules of certain plants (leguminosae) and of their bacteria in the phenomena of direct assimilation of nitrogen by plants; here also belong the discoveries of Schloesing and Laurent concerning the activity of microorganisms in the phenomena of soil nitrogen fixation; finally, here too belongs the discovery of the nitrogen-fixing bacillus made by Winogradsky.

All these remarkable works, just like the investigations of other scientists, reveal the full significance of Berthelot’s original assertion. “The starting point of nitrogen fixation must be sought not in the higher plants, but in certain lower microorganisms which live in the soil.”

In other parts of the vast field of agricultural chemistry Berthelot displayed brilliant activity. Together with Buignet he studied the formation of grape sugar in the tissue of fruits. He carried out investigations on the formation of ethers in wines and vinegar, on the chemical processes in plants occurring under the influence of light, and on soil chemistry, together with André.

Four thick volumes, which appeared in 1899, sum up Berthelot’s work in the field of agricultural chemistry.

History of Chemistry.

Berthelot’s works are predominantly philosophical; by this we mean that these works proceed from broad and profound ideas, and their practical embodiment

in reality was, in a certain sense, an adaptation to results obtained by experience. Berthelot’s activity did not consist of a consecutive series of precise experiments in the laboratory, unconnected with one another, isolated and standing apart; rather, it was a vast whole, governed by a general principle: the principle of the unity of the natural forces and the laws to which they are subject.

Berthelot, by the natural inclinations of his mind, was drawn into the study of the sources of human knowledge and wrote a series of works on the history of chemistry; this series is highly significant. As early as 1869 Berthelot began investigations on this question and set about collecting the necessary data. But only in 1885 did his book appear on the foundations of alchemy, on the Greek, Roman, and Arabic sources of it. Considerable development and clarification were brought to this work by the publication of the Collection of Ancient Greek Alchemists, based on a manuscript from the end of the tenth century, and by the publication of the book Introduction to the Chemistry of the Ancients and to the Chemistry of the Middle Ages. Three volumes were devoted by Berthelot to the chemistry of the Middle Ages. Then mention must be made of Archaeology and the History of the Sciences and, finally, of the book entitled The Chemical Revolution of Lavoisier. This book was an expansion of an address delivered at a public meeting of the Academy of Sciences in 1889, the address of which we spoke at the beginning of the present article.

Various Other Works

Marcelin Berthelot’s investigations also comprised a certain number of works connected only indirectly with the four principal directions that we have briefly examined. Among these the following may be mentioned: liquefaction of gases (1850), fractional distillation of liquids (1850), turpentine (1851/52), complex ammonias, polyatomic alcohols, compounds of mixed functions, etherification, closed vessels; sugars, laws of etherification; one of the laws of etherification subsequently became, thanks to the generalization of Guldberg and Waage, the law of mass action; coefficient of distribution; general method

hydrogenation of organic substances by the action of hydriodic acid acting at high temperatures, specific refractive power, supersulfuric acid, the action of electric discharges, allotropy, the origin of petroleum. Berthelot further studied specifically the phenomena of the action of ferments and the role of microorganisms in chemical reactions.

He established that the fermentation of beer converts grape sugar. His general ideas on fermentative actions present organized ferments as producers of the ferment proper, acting by a physicochemical route. He compared these phenomena with phenomena depending solely on the presence of a substance, and was thus drawn into the study of catalytic actions.

Berthelot’s encyclopedic knowledge, his broad general education, and his taste for generalizations were bound to lead him to work on quite diverse topics connected with philosophy, politics, history, education, and morality in their relations to science. He published: Science and Philosophy in 1886, Science and Morality in 1887, Science and Free Thought in 1905, and Science and Education in 1901.

1. In 1870 Berthelot was appointed chairman of the scientific committee for the defense of Paris. Later (1878) he became chairman of the Commission on Explosive Substances. ↩↩

2. Pierre Eugène Marcellin Berthelot, son of Jacques Martin Berthelot, doctor of medicine, and Ernestine Sophie Claudine Biard, was born on October 25, 1827, in Paris, in a house located on the Place de Grève; he died in Paris in the palace of the Institut de France on March 18, 1907. ↩