Chevreul, Michel Eugène

(b. Angers, France, 31 August 1786; d. Paris, France, 9 April 1889),

chemistry.

After his early education in Angers, where his father was the director of the medical school, Chevreul went to paris in 1803 to study chemistry under Nicolas Vauquelin at the Muséum d’Histoire Naturelle, thereby beginning a career of nearlly ninety years at that institution. Chevreul rose rapidly through the scientific ranks during the 1820’s and 1830’s, his two most important positions being those of professor of chemistry at the Museum from 1830 and director of dyeing at the Manufatures Royales dews Gobelins, the national tapestry workshop, where he succeeded claude Berthollet in 1824, for nearly sixty years he taught courses in chemnistry at these two institutions, he was director of the Museum from 1864 to 1879. Chevreul became a member of the Académie des Sciences in 1826 and was elected to the presidency in 1839 and again in 1871.

His countrymen admired the centenarian for his abilities in many different fields. Chevreul displayed his versatility in his many books and papers in histrory, philosophy, and psychology. He contributed many papers to the journal des savants on a variety of subjects, of which the most important were his studies on alchemy, the early history of chemistry, and the history of medicine. He wrote two books on these subjects: Histoire des connaissances chimiques(1866) and Resume d’une histoire de la matiere (1878).

Chevreul’s interest in psychology culminated in 1853, when the Académie des Sciences appointed him chairman of committee to investigate séances and other psychic phenomena, as well as the use of divining rods and exploring pendulums in locating water or mineral deposits. He published an expose of psychic phenomena and of these devices in his De la baguette divinatoire (1854). Chevreul also produced many papers on philosophy and on scientific method. His ideas on scientific method found their most complete expression in his De la methode a posteriori experimnentale(1870).

Chevreul was very regular and methodial throughout his long life. In his later years he continued to work at the Muséum and to attend meetings of the Aacademy, presenting his last communication to this body in 1888, when he was 102. He had married Sophie Davallet, the daughter of a tax official, in 1818. She died in 1862 and Chevreul forsook almost all social life, livin his remaining years in the Museum and going out only to scientific meetings. Because of his achievements and great age, his colleagues accorded him great respect and regarded him as one of the most distinguished scientists of the century. The French nation celebrated Chevreul’s centenary on 31 August 1886. It was a great national event conducted in the presence of the president of the Republic and of scientific delegations from all over the world. The Museum was the locale for the main ceremonies, which featured the unveiling of Chevreul’s statue and many discourses by dignitaries extolling his achievements. The festivities concluded and special performances at Paris theaters. His funeral some two years later at the cathedral of Notre dame attracted thousands of people.

Chevreul’s scientific researches on dyes, color theory, and the chemistry of natural fats all stemmed from his association with Vauquelin at the Museum. Vauquelin introduced Chevreul; to the study of organic substances in 1807 by having his student investigate plant dyes. This was Chevreul’s first important series of researces. He isolated and examined several naturaal dyes. On the completion of these studies in 1811 Chevreul turned to the chemistry of natural fats as his next project. This study of dyes upon his appointment the following year as director of dyeing at Gobelins.

Chevreul’s immediate task at Gobelins was to work on the improvement of color intensity and fastness in wools. He had been selected for this position because he was an outstanding chemist; and his initial studies were on the chemical aspects of dyes and dyeing, attempting to place the art of dyeing on a more rational basis than the complicated and empirical procedures then employed. He embarked upon a thorough study of the properties of natural dyes and between 1838 and 1864 published several important papers in the Memoires de l’ Academie des Lecons de chimie appliquee a la teinture (1829–1830) rendered an important service to the dye industry during the years prior to the advent of synthetic dyestuffs.

In addition to the chemical aspects of dyeing Chevreul made an intensive study of the principles governing the contrast of colors, which resulted in his monumental De la loi du contraste simultane des couleurs (1839), the most influental of his many books. This book was the outcome of his discovery that the apparent intensity and vigor of colors depended less on the pigmentation of the material used than on the hue of he neighboring fabric. After many experiments on color contrast Chevreul formulated for the hue of the neighboring fabric. After many experiments on color contrast chevreul formulated for the first time the general principles and effects of simultaneously. According to Chervrul, “where the eye sees at the same time wo contiguous colours, they will appear as dissimilar as possible, both in their optical composition and in the height of their tone. We have then, at the same time, simultaneous contrast of colour properly so called, and contrast of tone” (The principles of harmony and Contrast of Colours, p.11).

Under simultaneous contrast Chevreul included all the modifications that differently colored objects appear to undergo in their composition and tone. Furthermore, he diagramed these variations on a chromatic circle on which, out of the three primary colors of red, yellow, and blue, he defined almost 15,000 tones by first placing these three colors on equidistant radii of the circle and interpolating twenty- three color mixtures in each of the sectors. He thereby obtained a chromatic circle of seventy-two colors representing the entire visible spectrum. He then prepared additional circles by toning down colors with known proportions of black. To compare tones for each color, he mixed the normal colors with known proportions of black in one direction and white in the other, producing complete scales of colors, with pure white and pure black forming the extremes and the pure color the middle of the scale. In this way Chevreul believed he had met the need for precise standards in the definition and use of colors and a way of faithfully reproducing any tone of color. His circles and scales were valuable to the painter and dyer because they represented every possible color modification.

Indeed Chevreul designed his De la loi du contraste simultane less for scientists than for painters, designers, and decorators. He devoted much of the book to the applications of the principles of contrast to the various problems that the artist and designer encounter in the use of color and to the harmonizing of colors and their use as agents of pictorial harmony.

De la loi du contraste simultane was one of the most influential treatises on color written during the nineteenth century, even though it was never revised by its author and by the 1869’s was already antiquated as a scientific treatise. Physicists had studied color on empirical observation and experiments on color betapestries. Nevertheless, chevreul continued to be acclaimed for the discovery of several important priniciples governing color behavior.

Finally, one important aspect of Chevreul’s color studies must be mentioned: their influence in the finearts. The neo-impressionist painters derived their methods of painting from chevreul’s priniciples, applying separate touches of pure colors to the canvas and allowing the eye of the observer to combine them. Several artists hoped that the instinct of impressionists like manet and monet, who had dissociated tones on the canvas to enhance their brilliance, might be scientifically verified by the study of the physics and physiology of color perception. This “scientific” impressionism emerged in the 1880’s. It was based on the resolution of the colors of nature into the colors of the spectrum and their representation on the canvas by dots of unmixed pigments, these dots at a distance giving the effect and brilliance of natural light and not of pigments. The leaders of neo-impressionism were Geogres Seurat and Paul Signac. They found the scientific basis for the division of tones in Chevreul’s arguments for painting into pictures the effects of contrast based on nature’s behavior, his proofs, and his principles were all adopted by these artists. They limited their palettes to chevreul’s circle of fundamental colors and intermediate tones and applied colors scientifically to their canvases as oppposed spots. In May 1886, to make more explicit their unified aims as scientific impressionists, Seurat, Signac, Pissarro, and others hung their work together and created a new artistic language with canvases appearing for the first time painted solely with pure, separate hues in equilibrium, mixing optically according to a rational method.

While his color studies made him one of the most influential scientists of the nineteenth century, Chevreul’s work on the chemical nature of the natural fats established him also as one of the major figures in the early development of organic chemistry. When he began these studies in 1811, research in organic chemistry was in a very rudimentary state. Chemists had isolated many materilals from animal and plant sources and had investigated their chemical proper ties. These immediate principles were of a more complex nature than inorganic bodies and suposedly were the products of special forces in the organism, forces that were different from those in the inanimate world. The whole subject of animal and vegetable chemistry was in a state of confusion. Among the prerequisites to a removal of this confusion was a means of determining the elementary composition of organic materials, which were just beginning to succumb to elementary analysis when Chevreul embarked upon his investigation of animal fats. This was the first area of organic chemistry to receive a thorough examination, and Chevreul’s researches between 1811 and 1823 resulted in the natural fats’ becoming the first class of naturally occuring organic substances whose fundamental character was understood.

While animal fats and vegetable oils had been utilized since antiquity, expecially in the making of soaps, chemists had a accomplished little in clarifying the nature of the saponification process or in understanding the chemical nature of the ingredients and products. Chevreul began his exploration of this subject when he analyzed a potassium soap yielded a crystalline material with acidic properties. It was the first of the several fatty acids he was to discover, and it led him into a systematic investigation of animal fats. His studies appeared in a series of articles in the Annals de chimie and synthesized into an account of the chemistry of natural fats in his Recherches chimiques sur les corps gras (1823).

Chevreul obtained a whole series of new organic acids by decomposion the soaps derived from a varitety of animal fats. He isolated, studied, and named many of the members of the fatty acid series from butyric to stearic acid. By 1816 he had established that all animal fats yieleded both fatty acids and glycerol on saponification with alkali, the glycerol having earlier been observed by Scheele as a conversion product of several fats and oils.

After his discovery of the fatty acids Chevreul attacked the saponification process itself, and by a masterly interpretation of reactions, he unraveled its nature. All fats were resolvable into fatty acids and glycerol. Each of these saponification products was isolated and submitted to elementary analysis. Chevreul found that the sum of the weights of the saponification products surpassed that of the original at by 4 to 6 percent. Furthermore, his analyses revealed that these products contained the same quantity of carbon but more hydrogen and oxygen, in the proportion of water, than the fat. Chevereul concluded that saponification was essentially the chemical fixation of water. During this chemical fixation the alkali replaced the glycerol in its combination with the fatty acid. Thus soaps were combination of a fatty acid with an inorganic base and were therefore true salts.

These conclusions about saponification and the nature of fats and soaps were the outcome of a number of original techniques that Chevreul introduced into organic chemistry. He successfully isolated, purified, and analyzed fats, soaps, fatty acids, and glycerol, and achieved an understanding of the chemical nature of these different types of organic substances. To accomplish these difficult tasks, Chevreul had to develop his own methods of separating the constituents of natural fats and of indentifying closely relatd orgnic acides in mixtures of considereable complexity. By the careful use of solvents, he developed methods of fractional solution to separate the immediate principles in fats. He separated the mixtures of fatty acids on the basis of their differing solubility in a given solvent, purified them by repeated crystallization, and determined their purity by the constancy of their melting point. Chevreul thus was chiefly responsible for introducing the melting point as a useful means of establishing the identity and purity of organic substances.

His Recherches chimiques sur les corps gras is mainly experimental and descriptive. Chevreul was reluctant to go beyond his observations and the immediate inferences from them. It was only at the end of the book that he proposed his conjectures relative to the arrangement of the elements in natural fats. In addition to the conclusions concerning saponification. Chevreul inferred that fats were comparable to esters. They were compounds of a fatty acid and the alcohol gylycerol. Like esters, they were neutral substances, and under the influence of alkali they yielded and alcohol and an acid. Exactly what kind of alcohol was glycerol and what kind of esters were fats remained an open question until Marcellin Berthelot in the 1850’s synthesized the immediate principles of fats by combining glycerol with different fatty acids, showing that one equivalent of glycerol can unite with three equivalents of fatty acid and that it has, therefore, a triple alcoholic function.

Chevreul’s Recherches is a full account of the chemistry of fats. He had revealed the nature of a large and important class of organic substances and had shown that they were composed of a few chemical species which were amnable to analysis and obeyed the same laws of chemical combination followed by the simpler substances in the inorganic realm. The book is a model of complete, exhaustive research in organic chemistry. Few areas of chemistry at this time had been so thoroughly explored. Although his studies were follwed by those of many chemists, who extended the number of fatty acids isolatable from fats and oils there was no one comparable to Chevreul in this field until Thomas Percy Hilditch in Great Britain, a century later.

Following the completion of his investigation of natural fats, Chevreul wrote a work of a more general nature, Considerations generales sur Panalyse organique (1824), which is a reflection on the many years of research with organic materials. Here Chevreul considered the methods of research in organic chemistry, methods that he himself used with such success in his investigations. The primary analytical problems, were how to determine whether one had a pure substance or a mixture and how to resolve the frequently complex animal or plant material into its immediate principles. It was Chevreul who placed this immediate principles. It was Chevreul who placed this immediate analysis on a rigorous basis. He considered the methods used in handling natural products, in isolating pure substances from them in altered form, and in recognizing their purity. He gave precise criteria for what constituted a pure organic compound and presented for the first time a clear and accurate account of the methods of immediate analysis that must necessarily preceed elementary analysis. Indeed, the foremost recognizing that he introduced into organic chemistry the fundamental concept of the immediate principle endowed with constant and definite properies and composition, from which no other material could be separated without altering the principle.

Prior to Chevreul’s work there was no method of submitting the products of analysis to a system of tests to determine whether the products were pure principles. Chevreul applied such a system of tests in his study of fats, which thereby became the first exact model of analytical research in organic chemistry. In the opinion of his contemporaries. Chevreul’s studies constituted the best work done in organic chemistry, wherein quantitative and atomic relations had been established, constitutions discovered, relationships discerned, and the way shown toward the clarification of the difficulties of organi chemistry.

BIBLIOGRAPHY

1. Original Works. An extensive bibliography of chevreul;s published writings was issued on the occasion of his centenary by Godefroy Malloizel, Oeuvres scientifiques de Michel-Eugène Chevreul 1806–1886 (paris, 1886). There is also a collection of unpublished material available: E. Chevrul, Quelques notes et letter de M. E. Chevreul (Dijon, 1907). Of Chevreul’s many books and articles the most significant are his two books on organic chemistry and the one on color theory: Recherches chimiques sur les cops gras d’orgine animale(Pair’s 1823) Considérations générales sur I’ analyse orgnique et sur les applications (Paris, 1824)’ De la loi du contraste simultanedes couleus et de I’assorliment des objets colorés (paris, 1839) There are two English versions of the latter book: The Principles of Harmony and Contrast of Colours, Charles Martel, trans, (London, 1854; 3rd., ed., 1872), and The Laws of Contrast of Colour, John Spanton, tran. (London, 1858).

Mention should be made of Chevreul’s historical, philosophical, and psychological studies: De la Baguette divinatoire, du pendule dit explorateur et des tables tournantes, aupoint de vue de i’histoir, de la critique et de la méthode expérimentale (Paris, 1854); Histoire des connaissances chimiques (Pais, 1866); De la méthode a posterioril expérmentale et de la generalite de ses applictions (Paris, 1870); Résumé d’une histoire de la mattere depuis les philosophes grecs jusqu’a Lavoisier inclusivement (Pairs, 1878).

II. Secondary Literature. There are many essays on the life and work of Chevreul. An excellent biography is Georges Bouchard’s Chevreul (1786–1889), Le doyen des savants qui vit au cours d’un siecle quatre rois, deux empereturs, trois républiques, quatre révolutions(Paris, 1932). Chevreul’s granddaughter, Mme. de Champ, collected a number of personal remembrances in her Michel-Eugene chevreul, vie intime (paris,1930) Marcellin Berthelot analyzed the principal scientific contributions of Chevreul in the official biography of the Academie des Scienes; “Notice historique sur la vie et les travaux de M. Chevreul,” in Memoires de I’Academie des sciences, 47 (1904), 388–433. A modern study that emphasizes Chevreul’s Pioneer of Organic Chemistry (Madison, Wis., 1962).

For Chevreul’s historical writings see George Sarton, “Haefer and Chevreul”, in Bulletin of the History of Medicine, 8 (1940), 419–445; and Hélène Metzge, “Eugéne chevreul, historien de la chimie,” in Archeion, 14 (1932), 6–11. Joseph Jastrow examined Chevreul’s study of psychic phenomena in “Chevreul as Psychologist,” Scientific Monthly, 44(1937), 487–496. An excellent study of scientific impressionism which provides an analysis of scientific impressionism which provides an analysis of Chevreul’s color experiments and theory is William Innes Homer, Seurat and the Science of Painting (Cambridge, Mass, 1964), pp. 20–29.

Albert B. Costa

Chevreul, Michel

FRENCH CHEMIST
1786–1889

Michel-Eugène Chevreul was a chemist whose career spanned the greater part of the nineteenth century. He was born in Angers, France, on August 31, 1786, and died in Paris on April 9, 1889. Chevreul's father was a wellknown physician. Raised in the midst of the terror of the French Revolution, Chevreul witnessed much violence and suffering. As a result, he maintained a lifelong aversion to politics and at an early age decided to devote his life to chemistry.

Chevreul's career as a scientist began at age seventeen when he became an assistant in the laboratory of Louis-Nicolas Vauquelin at the Muséum National d'Histoire Naturelle in Paris. While working in Vauquelin's laboratory, Chevreul began his study of organic chemistry with the investigation of the separation of natural coloring agents from their sources. At the age of twenty-four, he was named assistant naturalist at the museum. Chevreul then served as director of dyeing at the Manufacture Royale des Gobelins from 1824 to 1885. He became a member of the Academie des Sciences in 1826 and its president in 1839 and 1867. When Vauquelin retired, Chevreul attained the chair of chemistry at the museum, a position he held until his death in 1889.

Chevreul's career exemplifies the enormous strides made in the understanding of chemistry during the nineteenth century. He established the melting point as a key criterion for the purity of a substance. Even in the contemporary world, the melting point remains the first property determined to characterize a new solid. Chevreul excelled at the elemental analysis of organic substances and established the molecular formulas for many important chemical compounds. This procedure was considered very difficult in his time. His mentor, Vauquelin, had demonstrated that all foods are of four types: fats (lipids ), proteins, starches, and sugars. In his continued studies of fats, Chevreul used the above procedures, along with various methods of purification for substances with animal origins, to identify several of the fatty acids as pure substances with consistent molecular formulas.

Chevreul also contributed to the improvement of the ancient art of soap making. He identified soaps as the potassium salts of the fatty oleic and

stearic acids and animal fats from which soaps were derived as esters of the alcohol glycerol. This led to the replacement of potassium carbonate (potash ) in soap manufacture with the cheaper and more reactive sodium hydroxide (lye), which became available commercially in the early 1800s. The reaction for the manufacture of soap, saponification, is shown in Figure 1.

see also Fats and Fatty Acids; Soap.

Lawrence H. Brannigan

Bibliography

Aftalion, Otto (1991). A History of the International Chemical Industry, Theodor Benfey. Philadelphia: University of Pennsylvania Press.

Farber, Eduard (1952). The Evolution of Chemistry: A History of Its Ideas, Methods, and Materials. New York: Ronald Press.

Internet Resources

Cyberlipid Center. Available from <http://www.cyberlipid.org>.

"Michel-Eugène Chevreul." Catholic Encyclopedia. Available from <http://www.newadvent.org/cathen/03650b.htm>.

Chevreul, Michel Eugene (1786-1889)

French chemist, expert on color theories, researcher on animal fats (culminating in discovery of margarine), Michel Eugene Chevreul was born on August 31, 1786 in Angers, France. Chevreul conducted experiments on behalf of the French Academy of Science on divining by means of a pendulum. In his book De la baguette divinatoire (1854) he concluded that the movements of a pendulum in response to questions are the result of involuntary muscular movements in the hand induced by mental processes.

"Chevreul's pendulum" is often cited to disprove the reality of the information obtained by such devices as pendulums or divining rods, much as Michael Faraday 's similar explanations for table-turning in Spiritualist séances. Although it seems likely that Chevreul was correct in his investigation of some of the mechanisms of pendulum divining, and also in his assumption that mental processes may affect the pendulum movement, there is equal evidence of paranormal information obtained by the pendulum or divining rod when suggestive factors are not operating.

Chevreul's scientific discoveries made him an international treasure, which was made evident on his 100th birthday celebration given by France and England and his funeral held at Notre Dame Cathedral. He died on April 9, 1889 at the age of 102.

Sources:

Bird, Christopher. The Diving Hand. New York: E. P. Dutton, 1979.