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Claude Louis Berthollet: A Great Chemist in +he french Tradition.

The remarkable accomplishments of a leading French chemist of the late eighteenth and early nineteenth centuries are summarized in this paper.

Claude Louis Berthollet was born in Savoy, Italy, of French parents, in 1748, and died in Arcueil, near Paris, in 1822. He was naturalized as a French citizen in 1780 [1]. He studied medicine at the University of Turin and graduated from there with a doctoral degree at the early age of 22. He began his career as a physician, but shortly thereafter his interest turned to the field of chemistry where he was to remain for the rest of his life. Interestingly, Berthollet's famous compatriot Marcellin Berthelot (1827-1907) also started off in medicine but quickly changed to chemistry [2]. Berthollet moved to Paris for further study and later collaborated scientificallywith the celebrated chemist Antoine Laurentde Lavoisier (1743-1794). In 1785, he adopted Lavoisier's new oxygen theory of combustion, being the first French chemist to do so [3]. During the French Revolution, he wisely stayed away from all political activity and thus avoided the fate of the unfortunate Lavoisier at the merciless hands of Madame La Gu illotine.

Berthollet became ad joint chimiste del' Acadmie des Sciences in 1780, associe in 1785, pensionnaire in 1792, professeur de chimie at Ecole polytechnique in 1794, and membre de l'Institut de France in 1795. After the death of Lavoisier, he took on the role of the leading chemist in France. He accompanied Napoleon Bonaparte as a scientific advisor during the military campaigns in Italy and Egypt (1798-1800). He owned a villa in Arcueil where, together with the famous mathematician/scientistPierre-Simon, marquis de Laplace (1749-1827), he founded the Societe d'Arcueil, a private interdisciplinary discussion group with access to a well-equipped laboratory, and having its own scientific journal. The many important contributions of Berthollet received due recognition at the highest level. He was one of the "grands hommes de science" honoured by the Emperor Napoleon [4], and became "Comte sous l'Empire" [1].

Research on the Nature of Acids

Berthollet suggested the idea of an antagonistic force between acids and alkalis [5], resulting in reciprocal affinity. His careful investigations between 1785 and 1796 on the composition of acids led him eventually to reject Lavoisier's theory that oxygen was the essential principle of acidity. In 1785, he thought that oxidation of muriatic acid with manganese dioxide gave rise to oxymuriatic acid (chlorine), and in 1786 found that exposure of an aqueous solution of oxymuriatic acid to sunlight liberated oxygen and left behind muriatic acid. Berthollet concluded that oxymuriatic acid was made up of muriatic gas and oxygen, and this wrong interpretation was generally accepted for almost 20 years [6].

In 1787, Berthollet showed by analysis that, surprisingly, prussic acid did not contain oxygen [5]. After his later discovery of the acidic properties of sulfuretted hydrogen, which again did not contain oxygen, Berthollet became convinced that Lavoisier's acid theory was incorrect. His work on these last two compounds "proved of great value in arriving at the true theory of acids" [7].

Work for the Chemical Industry

Technical and scientific investigations were said to be of equal interest to Berthollet [8], which probably explains why he was so active in the industrial area. During the French Revolution, he succeeded in improving the centralized production of saltpeter, an essential ingredient in gunpowder, to such an extent that the old method of extraction was abandoned [4]. His contributions to the French chemical industry were numerous and aided the Napoleonic economy considerably, which is one of the reasons why Berthollet was so honoured by a grateful Emperor. He was particulary active in the bleaching and dyeing industries.

Together with fellow chemist and compatriot Jean Antoine Chaptal (1756-1832), who worked mainly on technical problems such as the production of alum and saltpeter, Berthollet pioneered the use of the decolourizing properties of oxymuriatic acid (chlorine) in the artificial bleaching of textiles [9], and launched that industry on a practical basis. In order to favour the development of bleaching, Berthollet initiated the use of volumetric analysis to control the chlorine content ofJavel water [4]. He also devised simple control procedures that could be carried out by ordinary workmen without calling upon specialists. Various bleaching agents were manufactured and were regarded as compounds of basic oxides and chlorine [10].

In 1784, Berthollet became the worthy successor of the conservative chemist Pierre Joseph Macquer (1718-1784) in the influential governmental post of director of the dyeing industry of France, a sector which had benefited directly from his own extensive research.

The Challenge of Chemical Affinity

The mystery of chemical affinity presented a formidable challenge and Berthollet was intrigued by it. He developed his controversial concepts concerning this aspect only after many years of thought and investigation, and presented these ideas for the first time in 1799. His research work in this regard has been stated to be his main contribution to chemistry [6]. He considered affinities to be physical forces that were related to that of gravity, and, thus, thought that Newtonian forces were involved in chemical attraction. The great French chemist Jean Baptiste Andre Dumas (1800-1884) later recognized that the inspiration for Berthollet's work on chemical affinity had been of Newtonian origin [11]. Berthollet thought of chemical systems as stationary analogues of the solar system, the forces between the bodies being in equilibrium [12]. In fact, he based his study of chemical reactions on the principles of mechanics and physics [7].

Like Lavoisier before him, Berthollet looked upon chemical combination as the mutual or reciprocal satisfaction of affinities. He realized that affinity was not an absolute force, and that the course of chemical reactions was influenced by numerous other factors such as temperature, solubility, volatility, elasticity, cohesion, physical state, and mass. It is now generally agreed that Berthollet's studies on affinity contributed greatly to our understanding of chemical reactions and of their raison d'etre.

Reversibility and Chemical Equilibrium

During his stay in Egypt (1798-1799), as one of a group of scientific advisors to Nepoleon Bonaparte, Berthollet made a striking observation that was to have, eventually, far-reaching consequences for chemistiy. He noticed large deposits of sodium carbonate in the salt lakes, and realized that they were the result of the reaction of highly concentrated sodium chloride solution with dissolved limestone. This reaction was the exact opposite of that observed in the laboratory in which sodium chloride and calcium carbonate were formed spontaneously from sodium carbonate and calcium chloride. Berthollet knew that the conditions in the salt lakes were unusual in that both reactants were present in very large quantity. He was the first to suggest that a chemical reaction might be reversible [13]. However, this original proposal made little impact on his contemporary chemists, and reversible reactions consequently received scant attention until as late as the research on the formation of esters by Marcellin Berthelot and co-workers in 1863 [2].

Naturally, Berthollet pondered the cause of such reversibility and wished to find out if the phenomenon had wide-spread existence. Upon his return to France, he began a systematic study of chemical reactions using acids and bases under a great variety of conditions. He used reaction mixtures in different proportions and then analyzed the products. Berthollet found the concentration changes and different conditions could reverse the direction of a reaction, and more significantly, change the relative amounts of reactants and products in equilibrium mixtures [14]. He recognized that chemical changes are frequently incomplete, with equilibrium being reached. The influence of changing quantities, i.e. the mass effect, actually represented the Law of mass action, but, alas, the results were not entirely clear, and their significance was missed for more than 50 years [15]! Following the careful research work of Max Guldberg (1836-1902) and Peter Waage (1833-1900), the Law of Mass Action was announced by the latter in 1867.

The Chemical Composition Controversy

Unfortunately, Berthollet went on to draw some wrong conclusions from his work on reversibility and chemical equilibrium because of poor analyses and consequent confusion of mixtures with pure compounds. He thought that solutions were compounds of indefinite proportions ("la dissolution est une veritable combinaison") [10], and believed that certain compounds varied in composition according to their method of preparation [16].

In 1799, Berthollet announced that the composition of some compounds could vary within small limits. This brought forth an almost immediate challenge from his colleague Joseph Louis Proust (1754-1826), professor of chemistry at Madrid (17891808), who, two years earlier, had announced that chemical compounds have fixed proportions and, thus, invariable compositions. Each of them set out to disprove the other by means of a good deal of analytical work and series of published research papers. A famous, but friendly, controversy developed between them and was to last about eight years. However, by 1808 it was Proust who prevailed, and the Law of Constant Proportions was generally accepted.

Other positive results deriving from the debate were: more accurate analyses and a better definition of chemical combination. The whole matter was settled by the appearance in 1807 of the atomic theory of John Dalton (1766-1844), which provided a rational explanation for the Laws of constant and also multiple proportions [17].

Berthollet soldiered on to the end and criticized the atomic theory and in particular denounced "I'arbitraire des regles de simplicite de l'hypothese de Dalton" [4]. Ironically, much later on, substances of indefinite composition, i.e., nonstoichiometric, such as alloys, were discovered to be common and appropriately became known as Berthollides.

The Analysis of Organic Substances

The first systematic studies on the composition of organic substances were reported by Lavoisier in 1786. He used the combustion method to determine quantitatively the carbon and hydrogen contents after having weighed the carbon dioxide and water liberated. Berthollet employed the same approach while attempting to improve it [13]. Lavoisier used Berthollet's results in conjunction with his own and proposed that organic compounds be defined as "combinations of oxygen with radicals that contained carbon and hydrogen" [14]. Berthollet assumed that the radicals of some organic acids might contain oxygen [10], but showed that "radical vinegar" was merely common vinegar saturated with oxygen. He also developed what became know as "Berthollet-type" distillations of organic materials [9].

Research in Other Areas

The scope of Berthollet's researches over a period of almost 40 years is quite remarkable, as shown by the examples listed chronologically in Table 1. He worked on the galvanic decomposition of water, a topic of wide interest at the end of the eighteenth century. He was of the opinion that electricity was "un agent dont l'energie sera peut-etre portee a un degre qu'on ne fait qu'entrevoir, et qui donnera le moyen de produire dans la formation et la decomposition des combinaisons chimiques des effets inattendus" [5]. This proved to be a most clairvoyant statement He studied the effects of radiant heat and of light on the hydrogen-chlorine reaction, and found that they were very different. Berthollet, among others, including Lavoisier, was keenly interested in the atmosphere and reasoned that its constant composition was caused by loose chemical combination between its elements [18].

In 1785, Berthollet investigated the composition of ammonia and carried out chemical reactions with it, e.g., finding that reaction with chlorine gave rise to mephitic acid. In the same year, he discovered hypochlorites, and two years later, explosive chlorates, such as potassium chlorate. Berthollet also pioneered the use of charcoal for the purification of water.

Literary Contributions

Berthollet was the author/co-author of numerous research papers which were published in journals such as Memories de la Societe d'Arcueil and Memoiries de l'Institut de France. He also wrote several important scientific reports and two books which became famous. He collaborated with his French colleagues Lavoisier, Louis Bernard Guyton de Morveau (1737-1816), a former phlogistonist, and Antoine Francois de Foureroy (1755-1809), professor of chemistry at Jardin des Plantes, to produce a new rational system for naming inorganic compounds based on Lavoisier's concept of oxygen as the fundamental acidifying principle. This resulted in the appearance of the book Methode de Nomenclature Chimique in 1787, which had a great positive impact on the subsequent progress of chemistry. Berthollet also worked with Lavoisier and other chemists to found the long-lived journal Annales de chimie, the first issue of which was published in 1789. This was an important organ for the dissemination of research results, and one to whi ch Berthollet contributed frequently over the years.

Berthollet's ideas on chemical affinity, equilibrium, and the effects of mass changes on chemical reactions were presented in his two books printed at the beginning of the 19th century. The first one, namely: Recherches sur les Lois de l'Affinite (1801), was quickly translated into German ( Uber die Casetze des Verwandtsachft in der Chemie, and then English. The second book Essai de Statique Chimique (2 volumes, 1803) contained Berthollet's most controversial theories, and became more well-known because it was soon translated into English, Italian, and German. The latter contribution has been referred to by Venable [7] as Berthollet's "Greatest service to science ...". Another significant literary work Elements de l'art de la teinture, published in 1791, was also described as "a notable service" [6].

Teaching and Students

Berthollet was not a particularly good teacher, "his lectures being too difficult for his students in whom he mistakenly assumed the same degree of intelligence as his own" [3]. Together with others, he taught a short revolutionary course on the manufacture of saltpeter and of canons. In his chemistry course in 1795 at the new Ecole normale in Paris, which was followed by many future teachers, Berthollet emphasized that the tendency of substances to react depended upon the concentration of the reactants [4].

Some outstanding students attended Berthollet's lectures, and went on to make their mark in chemistry. The following three examples suffice to illustrate this fact. In 1800, Joseph Louis Gay-Lussac (1778-1850) followed the chemistry course given by Berthollet at Ecole polytechnique, and attracted the attention of the latter to such an extent that he became his assistant. Later, in Berthollet's villa in Arcueil, GayLussac carried out an important series of experiments on reactions between gases, and was influenced by Berthollet when he proposed his famous Law of combination of gases. Louis Jacques Thenard (1777-1857), who later collaborated most successfully with Gay-Lussac in chemical research, and was professor of chemistry at Ecole polytechnique from 1804 to 1837, was also one of Berthollet's pupils. Another person who studied under Berthollet in 1804 in Paris was Christian Johann Dietrich von Grotthuss (1785-1822), who became a researcher and was the author of an important memoir containing a theory which explained the fact that galvanic decomposition products only appeared at the poles [5].

Conclusion

Claude Louis Berthollet, industrial innovator, devoted experimentalist, scientific traveller, prolific author, and senator, was a worthy successor to Lavoisier; and played a key role in the promotion of chemistry at a critical time in its development.

In 1832, Gay-Lussac [4] succinctly summarized Berthollet's work on reactions and chemical compounds as follows "Berthollet avait raison propos des reactions, elles produisent en general un equilibre entre constituants, qui depend des conditions de reaction; il avait tort en ce qui concerne les composes produits". However, even Berthollet's erroneous conclusion regarding chemical composition forced further research that led directly to the firm establishment of the Law of constant proportions.

It has been well stated that Berthollet "croise la grande histoire" [4]. He, who is also credited with the development of the Law of double decomposition of salts, will be best remembered for the long-lasting impact and chemical sophistication of his research efforts.

Brian Newbold, FCIC, now retired, was formerly executive vice president, dean of research, and founding head of the department de chimie at Universite de Moncton, Moncton, NB. In March 1999, he was promoted to the rank of professeur emerite en chimie at Universite de Moncton in recognition of his services. Newbold continues to teach part-time and also does historical research.

References

(1.) Velluz, L., Vie de Lavoisier, Librairie Plon, Paris, p. 231, 1966.

(2.) Newbold, B.T., 'Pierre Eugene Marcellin Berthollet: An Illustrious Pioneering French Chemist', ACCN, 1 (2):26-28, 1999.

(3.) Partington, JR., A Short History of Chemistry, 3rd. ed., Macmillan & Co., Ltd., New York, p. 154, 177, 1965.

(4.) Bensaude-Vincent, B. and I Stengers, Histoire des Sciences: Histoire de la Chimie, Editions La Decouverte, Paris, pp. 96100, 141,154, 1993.

(5.) Partington, J.R., A History of Chemistry, Vol.4.. Macmillan & Co., Ltd., New York, p. 25, 45, 175, 253, 1964.

(6.) Leicester, H.M. and H.S. Klickstein, A Source Book in Chemistry: 1400-1900, McGraw-Hill Book Co., Inc., New York, p. 192, 250, 1952.

(7.) Venable, F.P,, History of Chemistry, 3rd. ed., D.C. Heath & Co., Boston, p. 84, 1900.

(8.) Farber, E., The Evolution of Chemistry, 2nd. ed., The Ronald Press Co., New York, p. 129, 1969.

(9.) Brock, W.H., The Fontana History of Chemistry, Fontana Press, HarperCollins Publishers, New York, p. 194, 281, 1992.

(10.) Berthollet, C.L., Essai de Statique Chimique, Paris, i, 34, 59; ii, p. 199, 234, 1803.

(11.) Levere, T.H., Affinity and Matter: Elements of Chemical Philosophy 1800-1865, Clarendon Press, Oxford, p. 167, 1971.

(12.) Berthollet, C.L., Recherches sur les lois de l'affinite, Paris, 1801.

(13.) Garard, I.D., Invitation to Chemistry, Doubleday & Co., Inc., Garden City, New York, p. 201, 314, 1969.

(14.) Salzberg, H.W., From Caveman to Chemist, American Chemical Society, Washington, DC, p. 210, 226, 1991.

(15.) Lockemann, G., Histoire de la Chimie, Dunod, Paris, p. 199, 1962.

(16.) Asimov, I., A Short History of Chemistry, Anchor Books, Doubleday & Co., Inc., Garden City, NY, p. 72, 1965.

(17.) Leicester, H.M., The Historical Background ground of Chemistry, Dover Publications Inc., New York, p. 153, 1956.

(18.) Hartley, H., Studies in the History of Chemistry, Clarendon Press. Oxford. p. 64. 1971.
 Some scientific contributions of Claude Louis Berthollet.
Year Contributions
1780 Obtained metallic soaps by precipitation
1784 Carried out experiments on the new gas chlorine
1785 Determined the chemical composition of ammonia
1785 Prepared nitrous oxide from ammonium nitrate
1785 Suggested that oxygen liberated during photosynthesis originated from
 water
1785 Showed that oxygenated muriatic acid (chlorine) could be applied
 as a bleaching agent
1786 Found that chlorine water gave off oxygen when exposed to sunlight
1787 Demonstrated that prussic acid contained only carbon, hydrogen,
 and nitrogen
1789 Discovered that hydrogen sulfide did not contain oxygen
1796 Found that sulfuretted hydrogen had acidic properties
1799 Presented detailed ideas on chemical affinity
1802 Proposed that mercury fulminate was a compound of mercury,
 ammonia, and alcohol
1803 Distinguished between the chemical effects of heat and light
1809 Produced hydrogen by heating fused caustic potash with iron filings
1817 Carried out improved quantitative analyses of organic compounds
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Comment:Claude Louis Berthollet: A Great Chemist in +he french Tradition.
Author:Newbold, Brian T.
Publication:Canadian Chemical News
Article Type:Biography
Geographic Code:1USA
Date:Nov 1, 1999
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