kragh, helge - julius thomsen and classical thermochemistry

British Society for the History of Science and Cambridge University Press are collaborating with JSTOR to digitize, preserve and extend access to The British Journal for the History of Science.

http://www.jstor.org

British Society for the History of ScienceCambridge University Press

Julius Thomsen and Classical Thermochemistry Author(s): Helge Kragh Source: The British Journal for the History of Science, Vol. 17, No. 3 (Nov., 1984), pp. 255-272Published by: on behalf of Cambridge University Press British Society for the History of

ScienceStable URL: http://www.jstor.org/stable/4026622Accessed: 26-10-2015 22:29 UTC

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://www.jstor.org/page/ info/about/policies/terms.jsp

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected].

This content downloaded from 143.107.252.124 on Mon, 26 Oct 2015 22:29:20 UTCAll use subject to JSTOR Terms and Conditions

B3HS, 1984, 17

Julius Thomsen and classical thermochemistry

Helge Kragh*

Classical thermochemistry is inextricably bound up with the problem of chemical affinity. In 1851, when Julius Thomsen began his career in thermochemistry, the concept of chemical affinity had been in the centre of chemical enquiry for more than a century.' In spite of many suggestions, preferably to explain affinity in terms of electrical or gravitational forces, almost nothing was known about the cause and nature of affinity. In this state of puzzling uncertainty some chemists felt it more advantageous to establish an adequate experimental measure of affinity, whatever its nature was. One way of providing affinity with a quantitative description was by means of the heats evolved in chemical processes.

A thermochemical measure of affinity was first suggested by Germain Henri Hess who believed that the proper measure of chemical affinity was given by heats of dilution.2 The most important of Hess' results was his generalization known as the law of constant heat summation, orjust Hess' law, that the amount of heat developed in a chemical reaction is constant, regardless of whether the reaction proceeds directly or through a number of intermediate steps. Remarkably, this conclusion was announced at a time when the energy principle was not yet stated and the mechanical theory of heat was still in its infancy. In fact, Hess' results were based on a caloric conception of heat. In the early forties the idea of a general correlation and conservation of the forces of nature gained a strong appeal, until it was formulated in definite terms through the mechanical theory of heat. Helmholtz, in his classical work on energy conservation, pointed out that Hess' law is a simple consequence of the principle of conservation of energy.3 But apart from rather casual remarks the energy principle was not immediately applied to chemistry and was not well known to chemists in the late forties. Although the rising conviction of a basic unity between the forces of nature, including affinity, naturally stimulated interest in a

*Address: Magnolievangen 41, 3450 Aller0d, Denmark. ' T. L. Levere, Affinity and matter. Elements of chemical philosophy 1800-1865, Oxford, 1971. Of relevance

to the present subject are also V. M. Schelar, 'Thermochemistry and the third law of thermodynamics,' Chymia, 1966, 11, 99-124, and V. V. Raman, 'The permeation of thermodynamics into nineteenth century chemistry,' Indianjournal of history of science, 1975, 10, 16-37.

2 H. M. Leicester, 'Germain Henri Hess and the foundation of thermochemistry,' Y. chem. ed., 1951, 28, 581-583. Hess' papers are reprinted in Ostwald's Klassiker der exakten Wissenschaften, no. 9, Leipzig, 1921.

3 H. Helmholtz, Uber die Erhaltung der Kraft, Berlin, 1847, 32.


256 Helge Kragh thermochemical conception of affinity, Hess' calorimetric studies were not followed up to any extent. Consequently the thermochemical conception of affinity did not at once benefit from the new mechanical theory of heat.

The first large-scale series of calorimetric determinations of heats involved in chemical reactions, after those of Hess, were carried out in Paris by Pierre Antoine Favre and Johann Theobald Silbermann.4 They collected a large amount of thermochemical data, reporting hundreds of accurate measurements which in the two decades to follow constituted the main body of data for thermochemistry. But they hesitated in connecting their measurements with theoretical notions and did not succeed in providing affinity with a general and operational thermochemical definition. They ended up with identifying affinity with chemical stability, measured by the quantity of heat evolved by formation of a chemical compound from its constituents. Although the mechanical theory of heat was fully developed in 1852, Favre and Silbermann did not make use of it in their works. The mechanical theory of heat diffused slowly to France where it was generally accepted only from the mid fifties and applied in chemistry only a decade later, with the works of Berthelot.

At about the time when Favre and Silbermann made their measurements the relations between heat and chemical processes were also studied by a few other chemists. In England thermochemical studies were pursued by Thomas Graham, Thomas Andrews and Thomas Woods.5 However, the most important contributions to thermochemistry came from France and Denmark.

Julius Thomsen's early interest in thermochemistry may have been the result of the influence exerted by Ludwig August Colding and was perhaps also indebted to H. C. Orsted's general view of the forces of nature. Thomsen was, like Colding, a protege of Orsted6 who for years had conceived chemical affinity to be a force intimately correlated with other forces of nature, such as light, electricity and heat. Colding was a friend of Thomsen with whom he collaborated in matters of administration and technology. Probably Colding's occupation with the equivalent of heat and mechanical force had an impact on Thomsen's initiation of his research programme in which the principle of energy conservation was for the first time incorporated in chemical theory.

Thomsen published his system of a new thermochemistry in 1852-54.7 His ambition was to determine the absolute values of chemical forces by

4 P. A. Favre and J. T. Silbermann, 'Recherches sur les quantites de chaleur degagees dans les actions chimiques et moleculaires,' Ann. chim. phys., 1853, 37, 406-508.

5 Levere, op. cit. (1), 202. J. R. Partington, A history of chemistry, 4 vols., London 1961-1970, IV, 608-612.

6H. Kragh, 'Julius Thomsen and 19th century speculations on the complexity of atoms,' Annals of science, 1982, 39, 37-60. For Colding and his debt to Orsted, see P. F. Dahl, 'Ludwig A. Colding and the conservation of energy,' Centaurus, 1963, 8, 174-188. Extracts of Colding's work of 1851 is translated in B. Bruce Lindsay (ed.), Energy: historical development of the concept, Stroudsburg (Pennsylvania), 1975, 36 1-364.

7 J. Thomsen, 'Bidrag til et thermochemisk system,' Kgl. Da. Vid. Selsk. Skr., Mat.-Nat.Afd. (5), 1852,


Julius Thomsen and Classical Thermochemistry 257 means of thermochemical measurements and thus supply the vague concept of affinity with a new quantitative and operational meaning. In 1861 he stated his programme as follows:

By considering the amount of heat involved by the formation of a chemical compound as a measure of affinity, as a measure of the work required again to resolve the compound into its component parts, it must be possible to deduce general laws for the chemical processes, and to exchange the old theory of affinity, resting on an uncertain foundation, for a new one, resting on the sure foundation of numerical value.8

For the energy involved in a reaction Thomsen used various names; in his publications of 1852-54 he changed between 'affinity', 'chemical force' and 'thermodynamic equivalent'. Thomsen adopted as a fundamental assumption that the heat of combination of a compound has to equal the difference between the thermal affinities of the compound and those of its constituents; that is, the thermal affinity of energy is conserved. In his first series of papers he succeeded in showing, among other things, that Hess' law followed from his thermochemical theory, thus changing its status from an empirical generalization to a deduction from higher principles.

The basic principles of thermochemistry, as Thomsen saw them, were stated in 1854. First he proposed a new definition of affinity: 'The force which unites the component parts of a chemical compound is called affinity.... In order to split up a compound, to overcome the affinities, a force is necessary the quantity of which can be measured as the amount of heat evolved in the formation of the compound from its constituents in question.'9 Conceiving a chemical process to be an exchange of affinities in which the weaker affinities are replaced by stronger ones, Thomsen concluded that 'Every simple or complex action of a purely chemical nature is accompanied by evolution of heat."0 This general statement, known as Thomsen's principle, became the much discussed backbone of thermochemistry in the decades to follow. The phrase 'of a purely chemical nature' was crucial in Thomsen's formulation, introduced as a protection against the objection that although most chemical processes evolve heat, some do not and thus seem to contradict the principle. In 1854 endothermic processes were well known and Thomsen discussed himself a number of processes which are followed by absorption of heat. He argued however that these processes were not of a 'purely chemical nature' and hence outside the realm of his principle. 'I see only chemical actions in such

3, 115-165; 'Die Grundzuge eines thermochemisches Systems,' [Poggendorf's] Annalen, 1853, 88, 349-362; 90, 261-288; 91, 83-104; 92, 34-57.

8J. Thomsen, 'Om de chemiske processers almindelige character og en pa denne bygget affinitetslaere,' Kgl. Da. Vid. Selsk. Oversigter, 1861, 100-134, on 104.

9'Grundzuge,' op. cit. (7), 1854, 92, 34. '0 Ibid., 36.


258 Helge Kragh processes where the substances combine in definite proportions, according to their number of equivalence, and I will only consider these in order to test the theory by experience."' Thomsen's attempt to protect his principle by means of the rather vague and arbitrary criterion of what a chemical action is, was much criticized later on. Many chemists felt that it was plainly ad hoc, tending to make the principle irrefutable and hence unscientific. Indeed, Thomsen's criterion for what should be counted as a purely chemical action was not only vague, but he also stated it in incompatible versions.'2

In later publications Thomsen often stressed that his system of thermochemistry was an empirical generalization and hence independent of the nature of matter and affinity. But Thomsen was always a firm proponent of atomism and believed that ultimately the nature of affinity would find its explanation in the mechanics of atoms.'3 In 1853 he offered a tentative explanation of affinity in terms of atomic motions, based on the principle of energy conservation.'4 In his later works he was however careful to stress that such atomic theories were still premature. As the dynamical laws of atoms were still unknown, the task would have to be left for the future, he concluded.

It was only from 1866, when Thomsen was appointed professor at the University of Copenhagen, that he was able to continue his work of 1852-54 and develop it experimentally. From 1866 to about 1886 Thomsen performed an extensive research programme in experimental and theoretical thermochemistry, publishing a steady flow of papers to Danish and German journals. The bulk of Thomsen's results was collected in the monumental four-volume work Thermochemische Untersuchungen, published 1882-86. Thomsen wrote his most important papers in German language and felt at home in the German scientific tradition. Among his more than 230 publications, 140 were published in German periodicals, only one in an English journal and none in French scientific journals.

Thomsen's thermochemical measurements covered most groups of organic and inorganic substances and resulted in a wide range of applications. Of particular importance was his confirmation of 1869 of Guldberg and Waage's recently developed law of mass action. 5 Thomsen was able to show that in the case of partial decomposition of salts, Guldberg

"Ibid. 12 In the Danish version of 1852 a purely chemical action was stated to be one which is 'solely caused

by the innate forces of the substances' (p. 157). Thirty years later the criterion read that the process 'proceeds without the expenditure of external energy and is accomplished only through striving of the atoms towards more stable equilibrium.' J. Thomsen, Thermochemische Untersuchungen, 4 vols., Leipzig, 1882-1886, I, 16.

3 See Kragh, op. cit. (6). 14'Grundzuge,' op. cit. (7), 1853, 90. 15J. Thomsen, 'Thermochemische Untersuchungen. I, Uber die Bertholletsche Affinitatstheorie,'

[Poggendorf's]Annalen, 1869, 138, 65-102. C. M. Guldberg and P. Waage, Etudes sur les affinitis chimique, Christiania (Oslo), 1867. E. W. Lund, 'Guldberg and Waage and the law of mass action,'J. chem. ed., 1965, 42, 548-550.


Julius Thomsen and Classical Thermochemistry 259 and Waage's theory was in good agreement with thermochemical measurements as interpreted in accordance with Thomsen's own ideas of thermochemistry. Although Thomsen's work did much to make the law of mass action accepted, Guldberg and Waage did not agree with Thomsen's thermochemical theory of affinity. The work of Guldberg and Waage was originally addressed to an understanding of chemical affinity. But during their work they realized that affinity is only one component among others determining the behaviour of a chemical process and that current efforts to provide a single measure of affinity, that being electrical, gravitational or thermal, were not satisfactory. In 1867 they criticized Thomsen's theory of affinity, though not mentioning their Danish colleague by name. 'The heat evolved during the reactions depends not only on the molecular heats of the reacting substances but also on the circumstances under which the reaction proceeds. ... if the circumstances can change the result of the reaction, then they necessarily cause, at the same time, changes in the evolved heat."6 Guldberg and Waage asked how the thermochemical concept of affinity could possibly account for the fact that in most reversible decompositions there is no net heat evolution.

II Ten years after Thomsen had completed his system Marcellin Berthelot in Paris began his extensive research in thermochemistry.'7 Berthelot's first study was followed by several book-length articles'8 and the whole work, experimental and theoretical, was collected in his Essai de mecanique chimique, published two years before the appearance of Thomsen's Untersuchungen. In these and later publications'9 Berthelot represented the science of thermochemistry as a French invention with himself as the chief inventor, an account which was bound to cause a collision with Thomsen in Copenhagen.

Berthelot's own experiments in thermochemistry started in 1873. At that time he had already formulated the basic principles of thermochemistry, using as experimental evidence the investigations of Favre and Silbermann. The number and formulations of Berthelot's principles were subject to changes in his various publications but in their essence they affected two statements both of which were shown to be consequences of the mechanical theory of heat. According to Berthelot's 'principle of molecular work' the measure of chemical affinity was given by the quantity of heat evolved. In processes where external energy does not intervene this

16 Etudes, op. cit. (15), 15. 17 M. Berthelot, 'Recherches de thermochimie,' Ann. chim. phys., 1865, 6, 290-464. M. P. Crosland,

'Berthelot, Pierre Eugene Marcellin,' in C. C. Gillispie (ed.), Dictionary of scientific biography, New York, 1970-80, II, 63-72.

18 M. Berthelot, 'Nouvelles recherches de thermochimie,' Ann. chim. phys., 1869, 18, 5-201; 'Recherches calorimetriquesurl'etat des corps dans les dissolutions,' Ann. chim.phys., 1873,29,433-514; 'Sur les principes generaux de la thermochimie,' Ann. chim. phys., 1875, 4, 5-131, 141-213.


260 Helge Kragh quantity is a constant, depending only on the terminal states of the system. The principle of molecular work, a generalization of Hess' law of constant heat summation, was stated by Berthelot in 1865.20 The second principle which Berthelot considered the proper foundation of rational thermochemistry, was first stated in 186421 and, in greater detail, in 1869 and 1875. This 'principle of maximum work' or 'third principle of thermochemistry' states that 'Every chemical change accomplished without the intervention of external energy tends to the production of that body, or system of bodies, which disengages most heat.'22 The validity of Berthelot's principle of maximum work was, in its earlier formulations, restricted to certain classes of chemical reactions (e.g., only very fast ones) but from 1875 and later on he stated it as a very general principle which had to apply by necessity. He declared, for example, that the principle implies that 'every chemical change which can be accomplished without the aid of a preliminary work, and without the intervention of foreign energy, necessarily happens if it disengages heat.'23 Berthelot shared Thomsen's view that thermal processes were the result of energetic transformations. Affinity was conceived to be an innate attractive force, the heat of reaction due to a transformation of its energy from potential to kinetic form. This was the general view of classical thermochemistry, stated, for example, also by Dumas in 1868.24

The striking similarity between Berthelot's principles and those stated by Thomsen in 1853-54 was, according to Berthelot, a coincidence as he was not aware of Thomsen's works until years after he started his own research in thermochemistry.25 Thomsen felt however obliged to assert his own priority and to protest against Berthelot's claim of being the founder of the laws of thermochemistry. In 1872 he subjected Berthelot's work to a devastating criticism, bluntly characterizing it as 'fraud' based on 'uncritical armchair works'. The sad result of Berthelot's efforts was, Thomsen said, merely to have 'loaded the scientific journals with a countless number of false and totally unusable numerical values.'26 Though not directly accusing Berthelot of plagiarism, he concluded that Berthelot had done no more than restate the results found by himself twenty years earlier.27 Thomsen's attack resulted in a vehement response from Berthelot who maintained that his thermochemical principles were quite different

19 M. Berthelot, Essai de micanique chimiquefondie sur la thermochimie, 2 vols., Paris, 1879; Thermochimie: donnies et lois numerique, 2 vols., Paris, 1897.

20 Berthelot, op. cit. (17). 21 M. Berthelot, Lecons sur les mithodes genirales de synthise, Paris, 1864, on 399. 22 Berthelot, op. cit. (18), 1875, 52. 23 Ibid., 212. 24 M. Dumas, 'Remarques sur Faffinite,' Compte rendu, 1868, 67, 597-614, on 607. 25 Micanique chimique, op. cit. (19), I, X. 26J. Thomsen, 'Die vollige Unguldigkeit der von Berthelot ... berechneten Zahlenwerte,' Chem.

Ber. 1872, 5, 181-185, on 185. 2ij. Thomsen, 'Eine Prioritatsfrage bezuglich einiger Grundsatze der Thermochemie,' Chem. Ber.,

1873, 6, 423-428.


Julius Thomsen and Classical Thermochemistry 261 from those stated by Thomsen.28 Berthelot declared that Thomsen's principle, that every purely chemical action is usually accompanied by an evolution of heat, was a banality known for a century. His dismissal of Thomsen's principle as being of no scientific originality was also addressed to his compatriot Henri Saint-Claire Deville who in 1860, years before Berthelot, had proposed a thermochemical notion of affinity similar to that of Thomsen.29 The exchange of views of 1872-73 was only the beginning of a long and embittered controversy between the two chemists, lasting for more than twenty years. The real subject of the controversy concerned which of the two scientists should be credited as the founder and doyen of thermochemistry. Both Thomsen and Berthelot felt that this honour could not be divided between them.

Berthelot exerted a great influence on French chemistry in the later part of the nineteenth century.30 A little prior to Berthelot's first works in thermochemistry a special chair was created for him at the Collge de France and in the years to follow he worked hard to build up the image he wanted of himself, as the unrivalled pioneer within key branches of modern chemistry. In France, at least, the propaganda bore fruit, leaving the impression that thermochemistry was a creation of French chemists, headed by Berthelot and founded upon his principle of maximum work. Berthelot's principle and his conception of thermochemistry came to be associated with the prestige of French science.

Thomsen was from a small country without a great scientific and patriotic tradition; contrary to Berthelot, he was not at all interested in forming a school around him and his work in thermochemistry. Thomsen's scientific ambition was to gain recognition as the one who had provided thermochemistry with a solid theoretical foundation supported by reliable experiments. He liked to emphasize that his theoretical considerations as well as his thousands of calorimetric measurements were his own works, indebted to nobody but himself. By personality Thomsen was a fighting character, often arrogant and fiery and highly critical of views which differed from his own.3' He was unwilling to accept that other researchers could substantially improve the knowledge of thermochemistry which, he was inclined to think, was virtually completed with his own investigations. Thomsen's first contribution to thermochemistry was purely theoretical,

28 M. Berthelot, 'Sur la reclamation de priorite elevee par M. J. Thomsen relativement aux principes de la thermochimie,' Bul. soc. chim. Paris, 1873, 19, 485-489. 29 According to A. Wurtz (ed.), Dictionnaire de chimie, Paris, 1869-1870, II, 824. 30 See, e.g., the views of Paul Sabatier, Victor Grignard and Pierre Duhem as quoted in M. J. Nye, 'Berthelot's anti-atomism: a 'matter of taste'?' Annals of science, 1981, 38, 585-590. Also in A. Metz, 'La notation atomique et la theorie atomique en France a la fin du XiXe siecle,' Revue d'historie des sciences, 1963, 16, 233-239, on 236.

31 In obituary articles the personality of the deceased is often idealized. In Edward Thorpe's memorial lecture one reads however about Thomsen's 'cold and unsympathetic nature [which] evoked no warmer feelings.' E. Thorpe, 'Thomsen memorial lecture,'7. Chem. Soc. London, 1910, 97, 161-172, on 165. Similarly Niels Bjerrum, a student of Thomsen: 'Thomsen was of a vehement and fiery nature. He could rise against his opponents quite without self-command . . .,' N. Bjerrum, 'Julius Thomsen', Chem. Ber., 1909, 42, 4971-4988, on 4977.


262 Helge Kragh making use of hypotheses and imaginative reasoning. But he soon developed a predilection for the art of experimenting and took a pride in performing very accurate measurements. Indeed, Thomsen often expressed a strong, and sometimes naive, confidence in the value of experiments in deciding crucially between competing theories. He did not recognize that his own experiments were far from pure observations and that any conclusion derived therefrom involved in fact a complicated network of theoretical assumptions. Thomsen's 'experimenticist' predilec- tion32 and mistrust of hypotheses in chemistry is reflected in his controver- sies with Berthelot and other chemists over the significance of thermochemical measurements.

Thomsen's attack of 1872-73 on Berthelot's methods and scientific credibility was reiterated in 1878.33 Thomsen claimed that Berthelot was not only a bad experimenter but also a biased scientist who judged experimental values according to whether they agreed or not with his own doubtful hypotheses. Berthelot, on his side, not unexpectedly criticized Thomsen's measurements for being inaccurate and uninteresting.34 Favre, the Parisian veteran in thermochemistry, assisted Berthelot's cause by hinting that Thomsen's confirmation of the variation of the heat of reaction with temperature (Kirchoff's equation) was not an original work as it illegitimately relied on results first found by Favre.35 The persistent rivalry between Thomsen and Berthelot can be followed through many of their publications in the period 1872-1886. Neither of the two chemists wasted an occasion to point out the bad methods, illegitimate conclusions and inaccurate measurements of the other; or, conversely, to claim their own priority and competence. Instead of applying the results and methods of each other they jealously stuck to their own works and referred to the other mainly for the purpose of criticism. As a result of Thomsen's anti-French feelings Berthelot's bomb calorimeter for combustion in oxygen was never introduced in Thomsen's laboratory. Despite its advantages Thomsen would not accept the use of an apparatus developed by his Parisian rival. While Thomsen was aggressive and published several anti-Berthelot papers, the powerful Berthelot could afford the more discrete tactics of almost ignoring his colleague in Copenhagen. In Berthelot's voluminous writings on thermochemistry, Thomsen appears only as a very secondary and provincial figure.

In France Thomsen's case was supported by Pierre Duhem who had

32 Experimenticism is the extreme empiricist doctrine that experiments and accurate measurements have absolute priority in the analysis of scientific work. The term was introduced and exemplified by Gerald Holton in 'Einstein and the 'crucial' experiment,' Am.j. phys., 1969, 37, 968-982.

33 J. Thomsen, 'Ueber Genauigkeit thermochemischer Zahlenresultate,' Chem. Ber., 1878, 11, 2183-2188.

34 M. Berthelot, 'Sur la chaleur de dissolution du sulfate de soude,' Ann. chim. phys., 1878, 14, 445-452. 35 M. P. A. Favre, 'Reclamation relative a une note de M.J. Thomsen,' Bul. soc. chim. Paris, 1874, 21,

487.


Julius Thomsen and Classical Thermochemistry 263 his own reasons for doing so.36 Duhem felt that his career was blocked by the repressive authority associated with Berthelot's principle of which he always was a fervent critic. With the sole exception of Duhem, Berthelot's claim to be the founder of rational thermochemistry was accepted in France. In Germany and England Thomsen's merits were fully recog- nized.37 When the Royal Society in 1883 awarded the Davy Medal for pioneering contributions to thermochemistry,38 the honour was shared between Thomsen and Berthelot, no doubt to the dissatisfaction of both chemists.

The controversy between Thomsen and Berthelot was to some extent due to differences in scientific style and perspective. Both scientists advocated an empiricist method, emphasizing that scientific laws should be the result of observations and that hypotheses should be used very cautiously and only if they were closely linked to experiments. Thomsen tended to conceive the exact determination of thermochemical quantities as an end in itself and consequently judged experimental accuracy as the prime virtue of thermochemistry. Berthelot's attitude was less experimenticist. For him thermochemical measurements were interesting primarily because of their relevance for theoretical notions such as the principle of maximum work.39 Berthelot's positivistic outlook led him to deny the reality of atoms and molecules. Although Thomsen too held positivistic virtues in high esteem, he did not share Berthelot's anti-atomism. On the contrary, Thomsen was a firm believer in the reality of atoms and their significance in thermochemistry.

The rivalry between Thomsen and Berthelot may have been related to the political situation in Europe after the Franco-Prussian war. In France there was a widespread hostility against German science and what was felt to be Germany's attempt to obtain a monopoly in science. The prestige of French science was a constant preoccupation of leading French scientists, among them many chemists.40 A part of this prestige was Berthelot's principle of maximum work and French thermochemistry in general. Although Thomsen was not a German his thermochemistry was

36 P. Duhem, 'Thermochimie,' Revue des questions scientifique, 1897, 12, 361-392, on 363-364 and 368. Reviewing Berthelot's Thermochimie Duhem took the opportunity to launch a strongly worded attack on Berthelot and his position in French chemistry. According to Duhem, Berthelot's principle was a 'ridiculous tautology' (370). In 1884 Duhem's doctoral dissertation which contained an attack on the principle of maximum work was rejected as a result of its questioning thermochemical orthodoxy; it was published as a book two years later as Lepotentiel thermodynamique (Paris, 1886). See D. G. Miller, 'Pierre Duhem', Physics today, December 1966, 47-53.

37 M. M. Pattison Muir, Principles of chemistry, London, 1884; W. Ostwald, Lehrbuch der allgemeinen Chemie, 2 vols., Leipzig, 1892-1893, 11/1, 64; E. von Meyer, Geschichte der Chemie, Leipzig, 1889, 383.

38 Proc. Roy. Soc. London, 1883, 36, 74. 39 HarryJones, an American chemist of the Ostwald school, described Thomsen as 'the type of mind

that delights in accurate experimental work'; while Berthelot was 'not the type of mind to be limited to fine experimental work.... Berthelot made thermochemical measurements for a definite purpose, and that was to see to what far-reaching conclusions they would lead.' H. C. Jones, A new era in chemistry, New York, 1913, 36.

40 H. W. Paul, The sorcerer's apprentice. The French scientist's image of German science 1840-1919, Gainesville (Florida), 1972.


264 Helge Kragh closely linked to German science; all of his major publications, including the attacks on Berthelot, appeared in German.

III

A major part of Thomsen's thermochemical programme was directed to the problems of structural chemistry, in particular in organic chemistry.4' The general idea was to establish a connection between, on one hand, the assumed structure of a compound and, on the other hand, its heat of formation. Thomsen argued that when such a connection was established, comparison between the calculated value and the experimental value of the heat of formation of the compound in question would provide a test for theories of molecular structure. In order to work out this idea Thomsen made use of the general principles of thermochemistry and assigned definite thermal values, or strengths of affinity, to the various types of chemical bonds, irrespective of their position in the molecule. These thermal values were determined from the heats of formation of molecules of known structure which again were based on the experimentally known heats of combustion. For example, the heats of formation at constant volume of ethane and methane were found to be, in Thomsen's notation, (C2,H6) - 104 2 kcal and (C,H4) = 59-6 kcal. Denoting the thermal value of a single bond between two carbon atoms with v, and that of a bond between carbon and hydrogen with r, Thomsen assumed that (C,H4) = 4r and (C2,H6)= 6r+v, which leads to the result that v, is 14 8 kcal. Following this kind of reasoning Thomsen concluded that the amounts of heat which correspond to a single and a double bond are approximately the same and furthermore close to the thermal value of the C-H bond. The thermal value of the triple bond was found to be almost zero. This led to the rather strange conclusion that if two carbon atoms are united by two bonds, no energy is required to break one of the bonds; and in triply bound carbon atoms no energy is set free by their union. Thomsen thus thought to have shown that compounds which contain double or triple bonds according to the usual view, are, in fact, saturated. He also thought that his thermochemical method was able to settle the question of the structure of benzene.

This was one of the most discussed questions of structural chemistry, especially after 1866 when Kekule published his famous hexagon formula with alternating double and single bonds.42 Although Kekule's proposal remained the most favoured throughout the century it was contested from many sides. One of the alternatives which attracted considerable interest was due to Albert Ladenburg who in 1869 proposed a prismatic structure

41 J. Thomsen, 'Thermochemische Untersuchungen uber die Theorie der Kohlenstoffverbin- dungen,' Chem. Ber., 1880, 13, 1321-1334; Thermochemische Untersuchungen, op. cit. (12), IV.

42 A. Kekule, Lehrbuch der organischen Chemie, 2 vols., Erlangen, 1866, II, 496.


Julius Thomsen and Classical Thermochemistry 265 in which the six carbon atoms were held together by single bonds only.43 Thomsen now applied his new method of calculating heats of formation of hypothetical organic structures to the case of benzene. In 1880 he concluded that Kekule's formula was all wrong.4 Thomsen claimed that his thermochemical arguments against the double bond theory were conclusive, constituting a crucial test as to the structure of benzene and related compounds. 'The question concerning the constitution of benzol can now be given a decisive answer by means of experiments ... It can be decided with certainty whether a hydrocarbon contains only single bonds or partly single and multiple bonds.'45 Thomsen argued that according to his theory the heat of combustion of benzene would be 846 kcal if Kekule's structure was assumed. On the other hand, on Ladenburg's structure the heat of combustion was calculated to 802-3 kcal. In order to compare the two theoretical results with the actual heat of combustion of benzene, Thomsen redetermined this quantity with great care and found it to be 805-8 kcal, agreeing well with Ladenburg's formula but not with Kekule's. Consequently he concluded that 'The six carbon atoms of benzol are united to each other by nine single bonds, and the previous assumption of a structure of benzol with three single and three double bonds is not supported by experiment.'46

In 1887 Thomsen published his own model of benzene, based on an octahedral structure.47 Thomsen placed the six carbon atoms at the corners of a regular octahedron, each of the carbon atoms being connected to three others by one axial and two peripheral bonds. In that way he retained the symmetry and the nine single bonds the presence of which he thought to have proved experimentally. Thomsen's proposal did not win much support. With the one exception of Henry Edwards Armstrong no chemists of significance seem to have paid attention to it.48

Thomsen's ambitious programme of applying thermochemistry as a key to structural chemistry aroused considerable interest. Lothar Meyer wrote approvingly to Thomsen that 'if your experiments in mass action, in neutralization etc. have already shown that thermochemistry is suitable for something else than just the lengthy conversions a la Berthelot of negative heats of reaction into positive ones, then your structural researches now

43 A. Ladenburg, 'Ueber Benzolformeln,' Chem. Ber., 1869,2, 272-274. A diagonal structure, similar to that proposed by Ladenburg, was forwarded by A. Claus in his Theoretische Betrachtungen und deren Anwendungen zur Systematik der organischen Chemie, Freiburg, 1867, 207-208. For other candidates and background to the problem of the structure of benzene, see C. A. Russell, The history of valency, Leicester, 1971, ch. 9.

44J. Thomsen, 'Die Constitution des Benzols,' Chem. Ber., 1880, 13, 1808-1811; 'Zur Benzolformel,' Chem. Ber., 1880, 13, 2166-2168.

45 Ibid., 1810. 46 Ibid., 1811. 47J. Thomsen, 'Om benzolmolekylets konstitution,' Kgl. Da. Vid. Selsk. Oversigter, 1886, 179-186. 48 H. E. Armstrong, 'The determination of the constitution of carbon compounds from thermoche-

mical data,' Phil. mag., 1887, 23, 73-109. Armstrong proposed a 'centric' formula which agreed with the nine single bonds suggested by Thomsen.


266 Helge Kragh open up a very wide perspective which even the most dense aromatic fog of colour will not be able to obscure.'49 However, with few exceptions, such as Hans Jahn at the university of Vienna,50 the chemists did not accept Thomsen's thermo-structural theory.

In an extensive review of 1881 the American chemist J. P. Cooke judged Thomsen's work as 'a bold push beyond the beaten tracks of science.'5' But he concluded that chemical evidence, if taken together, supported Kekule's formula rather than Ladenburg's and that Thomsen's arguments did not prove the fallacy of Kekule's theory. Other chemists, such as D. I. Mendeleev and M. M. Pattison Muir, criticized Thomsen's confidence in his method and objected to the logic of his argumentation.52 In England, Thomsen's theory was also criticized by Armstrong and S. U. Pickering both of whom argued that Thomsen's conclusions tended to destroy the accepted bond theory of organic constitution.53 In contrast to their German colleagues, Cooke, Pattison Muir, Armstrong and Pickering did not dismiss Thomsen's reasoning completely; they found his theory important and suggestive and sought rather to modify it in order to bring it into accordance with accepted views.

After the appearance of volume four of Thermochemische Untersuchungen a much sharper criticism was launched from Germany. F. Stohmann published new measurements of the heat of combustion of benzene which differed from Thomsen's but were in good agreement with Berthelot's value.54 Thomsen at once objected to Stohmann's measurements but Stohmann continued to criticize Thomsen's accuracy.55 Stohmann was clearly irritated over what he considered as Thomsen's stubbornness; he claimed that Thomsen was not willing to discuss matters impartially. Stohmann was supported byJ. W. Bruhl in Freiburg who not only argued forcibly against Thomsen's conclusions concerning the structure of benzene but dismissed his entire thermo-structural theory as 'speculations'.

49 Quoted from Bjerrum, op. cit. (31), 4983. This letter, as well as most other letters and unpublished materials which Thomsen left at his death, seems to have been lost. The archive of the Royal Library in Copenhagen includes eight boxes with source materials on Thomsen but nothing of particular interest to the history of chemistry. The Wilhelm-Ostwald-Archiv in Berlin(GDR) owns a small number of letters from Thomsen to Ostwald.

50 H. Jahn, Die Grundsatze der Thermochemie, Vienna, 1882, 147. 51 J. P. Cooke, 'Notice ofJulius Thomsen's thermochemical investigation of the molecular structure

of the hydrocarbon compounds,' Am. j. sci., 1881, 21, 87-98, on 98. 52 Pattison Muir, op. cit. (37), 174f and 303f; D. I. Mendeleev, 'Ueber die Verbrennungswarme der

Kohlenwasserstoffe,' Chem. Ber., 1882, 15, 1555-1559. 53 Armstrong, op. cit. (48); S. U. Pickering, 'Note on the foregoing communication,' Phil. mag., 1887,

23, 109-112; 'On thermochemical constants,' Phil. mag., 1888, 26, 53-62. 54 F. Stohmann, P. Rodatz and H. Herzberg, 'Ueber den Warmewerthe des Benzols,' J. prakt.

Chemie, 1886, 33, 241-260. Stohmann adopted the calorimetric technique developed by Berthelot and his pupils; in 1887 he worked in Berthelot's laboratory where he was introduced to the bomb calorimeter.

55J. Thomsen, 'Ueber die Verbrennungswarme des Benzols,'Y. prakt. Chemie, 1886, 33, 564-567; F. Stohmann, 'Entgegnung zu vorstehender Abhandlung des Herrn Thomsen,' ibid., 568-576; 'Zur weiteren Beleuchtung der Untersuchungen des Herrn Julius Thomsen,' Y. prakt. Chemie, 1887, 35, 136-141. Exchange of views between Thomsen and Stohmann in

_'. prakt. Chemie, 1886, 34, 55-56.


Julius Thomsen and Classical Thermochemistry 267 In a sharp and detailed criticism Bruhl characterized Thomsen's theory as biased and totally out of contact with chemical reality.56

Thomsen's reputation, and with it his conception of thermochemistry, was shaken by the negative reception of his thermo-structural theory. Wilhelm Ostwald was indebted to Thomsen's works in thermochemistry which he ranked highly; he now asked if Thomsen's science had met its Waterloo in its attack on organic molecules.57 Ostwald thought yes. Naturally Thomsen was deeply affected by the criticism of Stohmann, Bruhl and others, especially as his competence as an experimenter was questioned while the organo-thermochemical measurements of Berthelot and his group did not meet with a similar criticism. But Thomsen was unwilling to accept any shortcomings of his own. He continued to claim his superiority also in the theory and practise of organic thermochemistry, complaining that his results were ignored while those of Stohmann and Berthelot and his pupils were accepted.58 When the American Frank W. Clarke in 1903 proposed a new thermochemical theory of organic substances which differed from Thomsen's, the ageing Thomsen rejected it as speculative, biased and useless.59 His rejection had the character of a deja vu as it contained the very same methodological objections which were raised against his own theory some twenty years earlier.

Thomsen's conservatism was nourished by his unfriendly character and preference for isolation. None of the younger generation of chemists had much contact with Thomsen who did not at all like the new wave in chemistry which threatened to make his life-work obsolete. For example, in 1887 Ostwald and Walther Nernst were able to point out a serious error in Thomsen's old determination of the heat of formation of mercury compounds.60 Ostwald argued from general and theoretical reasons that Thomsen's determination had to be wrong and asked Nernst to redeter- mine the heat developed when mercury unites with bromine. Nernst obtained a result which differed substantially from Thomsen's which was based on his theory of thermal affinity. Although Thomsen at once

56J. W. Bruhl, 'Kritik der Grundlagen und Resultate der sogenannten Theorie der Bildungswarme organischer Korper,' J. prakt. Chemie, 1887, 35, 181-204, 209-236.

57 W. Ostwald, Zs. phys. Chemie, 1887,1,201. Most of Ostwald's early contributions to chemistry were in the tradition of Thomsen whose approach to the problem of affinity inspired him much. For Ostwald's indebtedness to Thomsen, see W. Ostwald, Lebenslinien. Eine Selbstbiographie, 3 vols., Berlin, 1926.

58 Thomsen sought, apparently in vain, to convince Ostwald that his thermochemical data on organic substances were superior to those of Berthelot and Stohmann and ought to be republished in Zeitschriftfir physikalische Chemie. Referring to the omission of his organic data in the third edition of Landolt's physikalisch-chemischen Tabellen Thomsen protested against 'such an outrageous treatment from the side of one of the main works in German literature.' Letter from Thomsen to Ostwald, January 27, 1905. I am grateful to the Wilhelm-Ostwald-Archiv for sending me copies of the Thomsen-Ostwald correspondence.

59 F. W. Clarke, 'A new law in thermochemistry,' Proc. Washington Acad. sci., 1903, 5, 1-37; J. Thomsen, 'F. W. Clarkes neues thermochemisches Gesetz,' Zs. phys. Chemie, 1903, 43, 487-493.

60J. Thomsen, 'Thermochemische Untersuchungen, XVII,' J. prakt. Chemie, 1874, 11, 261-283; W. Nernst, 'tYber die Bildungswarme der Quecksilberverbindungen,' Zs. phys. Chemie, 1888, 2, 23-28.


268 Helge Kragh admitted his error6' he was much annoyed to see his thermochemical method defeated by the new physical chemistry. In a letter to Ostwald, Svante Arrhenius reported: 'I have recently received a small letter from Nernst; he will now travel even farther away from the seriously assaulted Thomsen. I had hoped that at least his inorganic works could rest in peace, but it seems not to be so.'62 At the time of the publications of Berthelot's CChimique mecanique and Thomsen's Untersuchungen, the high-spots of classical thermochemistry, several other textbooks on thermochemistry appeared, signifying what must have seemed the maturing of a successful branch of chemistry. However, the success was only apparent. In fact classical thermochemistry, as developed by Thomsen and Berthelot, was a degenerating research tradition already from about 1880, when it was met with insurmountable difficulties and increasing criticism. Ten years later the once so progressive Thomsen-Berthelot approach had virtually vanished from the research front. In the first volume of Zeitschrift fur physikalische Chemie Lothar Meyer read the epitaph over the approach of Thomsen and Berthelot. Meyer summarized: 'One has to recognize that the fundamental hypotheses of the thermal theory of affinity have not been supported by observation.... Many of the admirers of the thermal theory of affinity, until a few years ago throned in undisputed majesty far above all facts, will perhaps find it hard to see it fade away.'63

The concept of chemistry upon which classical thermochemistry rested was essentially that of mechanical reductionism: i.e., the goal of chemistry was considered to be the reduction of chemical phenomena to a level where they could be explained in terms of Newtonian mechanics. By means of the mechanical theory of heat and the associated theory of affinity thermochemistry was thought to provide an effective instrument in reaching that goal. Both Thomsen and Berthelotjustified their thermochemical theories by linking them to the Newtonian ideal. Similar views were held by other leading thermochemists: strongest, perhaps, by Alexander Naumann, professor at the university of Giessen, who published the first textbook in thermochemistry in 1869. Naumann based his account very closely on the mechanical theory of heat and Berthelot's principle of maximum work. He stated that 'The mechanical theory of heat seems .. . to be the most appropriate path in order to make chemistry approach its final goal, to formulate it as a mechanics of atoms.'64 A similar view was

61 Thomsen, Zs. phys. Chemie, 1888, 2, 21-22; letter from Thomsen to Ostwald, December 12, 1887 (Wilhelm-Ostwald-Archiv).

62 H-G. Korber (ed), Aus dem wissenschaftlichen Briefwechsel Wilhelm Ostwald, 2 vols., Berlin(GDR), 1961, II, 41.

63 L. Meyer, 'Die bisherigen Entwickelung der Affinitatslehre,' Zs. phys. Chemie, 1, 1887, 134-144, on 140 and 143.

64 A. Naumann, Grundriss der Thermochemie, Braunschweig, 1869, 2. An extended and updated version of Naumann's work, much in use in Germany, appeared in 1882 as Lehr- und Handbuch der Thermochemie. Friedrich Mohr wrote on chemical affinity in the same vein, see his Mechanische Theorie der chemischen Affinitdt, Braunschweig, 1868.


Julius Thomsen and Classical Thermochemistry 269 expressed by Jahn, whose exposition of thermochemistry was strongly indebted to the works of Thomsen. However, although Jahn saw thermochemistry as a method for explaining affinity in terms of a mechanics of atoms, he considered atoms to be methodological entities, not ontological ones. 'Atomism is not a dogma; it by no means states anything about the real constitution of matter but is a view which allows a description of the phenomena in complete correspondence with observations.'65 Jahn's anti-ontological atomism shows that classical thermochemistry, although founded upon the mechanical theory of heat, could well be conceived as indifferent as to the reality of atoms. That, in any case, was the view of Berthelot. He was a staunch advocate of mechanical chemistry but did not accept atoms as the ultimate building blocks of matter and certainly not as the precondition for a rational thermochemistry.66

Atomism or not, the foundation of classical thermochemistry was the Thomsen-Berthelot principle which gradually turned out to be untenable. Already in 1864 the Dutch scientist Schroder van der Kolk argued that many chemical processes are not in accordance with the Thomsen-Berthe- lot principle and that the energy is only one component among others in the measure of chemical affinity. Van der Kolk demonstrated that the results of Sainte-Claire Deville on incomplete thermal dissociation of compounds67 were incompatible with the thermochemical concept of affinity and concluded that 'affinity and heats of combination are impossible to deduce from each other.'68 The objections of van der Kolk made no more impact on thermochemical orthodoxy than did other contemporary criticism, such as the arguments of Guldberg and Waage. In the seventies other critical voices were raised with increasing intensity. Lord Rayleigh pointed out that the thermochemical theory of affinity did not accord with the theory of energy dissipation, and criticized chemists for not recognizing the importance of the second law of thermodynamics.69 The Russian chemist Alexei Potilitzin, an assistant to Mendeleev, attacked the Thomsen-Berthelot principle from an empirical position, arguing that it could not possibly account for the existence of endothermic and reversible reactions.70 In the early eighties the weight of these and other objections were generally acknowledged and the confidence in the thermochemical theory of affinity rapidly faded away. Pattison Muir expressed a general view when passing the following sentence over the

65Jahn, op. cit. (50), 205. 66 M. Berthelot, 'Atomes et equivalents,' Comptes rendus, 1877, 84, 1269-1276. M. J. Nye, Molecular

reality, London, 1972, 7. See also Levere, op. cit. (1), 207-211 and Nye, op. cit. (30). 67 H. Sainte-Claire Deville, Lecons sur la dissociation, Paris, 1866. 68 H. W. Schroder van der Kolk, 'Ueber die mechanische Energie der chemischen Wirkungen,'

[Poggendorf's] Annalen, 1864, 122, 439-454, on 452. 69 Lord Rayleigh, 'On the dissipation of energy,' Nature, 1875, 11, 454-455 (Royal Institution

lecture). 70 A. Potilitzin, Chem. Ber., 1879, 12, 2369-2374.


270 Helge Kragh theory: 'Until there is a more definite kinetic theory of affinity than has yet been proposed, it will not be possible to apply thermal methods, except in a general and broad way, to the questions suggested by the term affinity.'7' A contributory cause to the declining confidence in the thermochemical theory of affinity was no doubt its failure in elucidating the structure of organic compounds.

The experimental objections to the Thomsen-Berthelot principle, such as incomplete dissociation, reversibility, and spontaneous endothermic processes, had been known for many years but were for a long time disregarded by orthodox thermochemists. Although Thomsen and Berthe- lot claimed that the principle was derived from, and justified by, observations, in reality they took it to be self-evident. Experiments which did not agree with the Thomsen-Berthelot principle were explained away, either by classifying them as exceptions, lying outside the range of the principle, or by forcing them to agree with it by means of more or less artificial assumptions. However, the attempts to rescue the universality of the Thomsen-Berthelot principle could not help to appear more and more unsatisfactory and ad hoc as counter-evidence and other objections accumulated. In 1873 Thomsen reluctantly admitted that probably his theory had no general or absolute validity.72 In the early eighties the true nature of the Thomsen-Berthelot principle was explained within the framework of the new chemical thermodynamics.73 It was proved that the principle can only claim validity as an idealization under extreme conditions, viz. at the temperature of absolute zero. Thomsen now stated without reservation that his original view was only an approximation to the truth. 'The release of the affinities usually appears as a development of heat; however, the evolved heat of reaction often is not a reliable expression of the quantities of the released affinities.'74 The other champion of thermochemistry, Berthelot, was less inclined to give up his principle of maximum work the general validity of which he maintained for several years.75

For a decade or so thermochemical orthodoxy sought to maintain its former authority, coexisting with its young progressive alternative, physical chemistry, but keeping to its own standards.76 Eventually the

71 Pattison Muir, op. cit. (37), 446. For other contemporary criticism, see B. Rathke, 'Ueber die Principien der Thermochemie,' Abhandl. d. Naturf. Ges. zu Halle, 1882, 15, 197-227; L. Meyer, Die modernen Theorien der Chemie, 4th edn., Breslau, 1883; P. Duhem, Lepotentiel thermodynamique, Paris, 1886.

72 Thomsen, op. cit. (27), 428. 73 In particular through the works of Helmholtz and van't Hoff. H. Helmholtz, 'Zur Thermodyna-

mik chemischer Vorgange,' Sitzungsber. Akad. Wiss. Berlin, 1882, 1, 21-39, 825-836. J. H. van't Hoff, Etudes de dynamique chimique, Amsterdam, 1884.

74 Thermochemische Untersuchungen, op. cit. (12), II, 1883, 428. 75 In 1894 Berthelot admitted that the principle of maximum work has no general validity; he argued

that it was a primitive version of the law of entropy. M. Berthelot, 'Le principe du travail maximum et l'entropie,' Comptes rendus, 1894, 118, 1378-1392.

76 The controversy between thermochemistry and thermodynamically based physical chemistry will be the subject of a forthcoming paper of R. G. A. Dolby. I am grateful to Dr. Dolby for his critical remarks to earlier versions of the present paper.


J7ulius Thomsen and Classical Thermochemistry 271 inadequacy of classical thermochemistry was realized even by the few chemists who still worked within the tradition founded by Thomsen and Berthelot. Writing in 1903 Clarke tersely remarked that 'Few general conclusions of unimpeachable validity have been developed by thermochemical research, and so, of late years, the entire subject has fallen somewhat in disfavor.'77 Considered as front research classical thermochemistry had ceased to exist at about 1910.

V

In retrospect the history of classical thermochemistry is the history of the successful emergence, less successful defense and then gradual decline of a scientific idea until it was transformed and, in a new context, incorporated in a new powerful paradigm. Eventually the thermochemical concept of affinity disappeared without much ado. Evidence incompatible with it had been known for decades but the theory was not rejected simply as the result of counter-evidence and no crucial experiment was accepted as a falsifying instance. Rather the theory gradually lost its power and scientific interest under the combined pressure of accumulated empirical counter-evidence, conceptual criticism and new forms of scientific style. The thermochemical theory of affinity was not given up because it was replaced by another and better theory of affinity. The entire concept of affinity, for a century and a half regarded as a crucial problem in chemistry, seemed to have lost its magic; at the turn of the century it was no longer considered interesting to search for measures or models of chemical affinity.

The transformation of classical thermochemistry into chemical thermodynamics is in many respects representative for scientific change. Chemical thermodynamics a la Duhem or Gibbs was not merely a critical development of thermochemistry a la Thomsen or Berthelot but, concep- tually and stylistic, rather its negation. The change was not abrupt or complete but a process, or conflict, which lasted several years; and it was, at the same time, a generational conflict in which the younger generation developed its own paradigm which the older thermochemists would neither understand nor accept. Leading thermochemists like Thomsen and Berthelot had invested too much of their scientific prestige in orthodox thermochemistry to change to a new rival paradigm. Like most other chemists they lacked the mathematical background which could have helped them in appreciating the works of e.g. Gibbs. There were, furthermore, significant differences between the scientific world views of classical thermochemistry and the emerging physical chemistry. Thus the ideas of physical chemistry were based on an anti-mechanist and anti-reductionist programme which was opposed to the Newtonian ideal of the Thomsen-Berthelot approach. As regards Thomsen, the anti-atomism

77 Clarke, op. cit. (59), 2.


272 Helge Kragh

of many physical chemists was contrary to his deep-rooted belief in the reality of atoms. Although Berthelot shared the anti-atomism-but not the anti-mechanism of Ostwald, Duhem and others, his view on chemistry was incompatible with that of physical chemistry. According to Berthelot physics and chemistry were separate sciences, with separate aims and methods.78 He believed that progress in chemistry could be ensured by widening the gulf between physics and chemistry; not by narrowing it as was the programme of physical chemistry. A programme to which Thomsen, for his part, had no objections.

78 Nye, op. cit. (30).

Books concerning the History of Medicirte, Natura4

Pure anrd Applied Scince Cataloguies isstued- desidterata lists welcome

MICHAEL PHELPS ?+++ ANTIQUARIAN BOOKS 19 CHEIVERTON ROAD PUTNEY LONDON SW15 1RN ENGLAND ?

Teleplhonie: 01-785 6766 Cables: 1PHELOBOOKS LONDON SW15


Article Contentsp. [255]p. 256p. 257p. 258p. 259p. 260p. 261p. 262p. 263p. 264p. 265p. 266p. 267p. 268p. 269p. 270p. 271p. 272

Issue Table of ContentsThe British Journal for the History of Science, Vol. 17, No. 3 (Nov., 1984), pp. 255-350Volume Information [pp. 347-350]Front Matter [pp. 294-294]Julius Thomsen and Classical Thermochemistry [pp. 255-272]L'esprit de la science anglaise et les Franais au XIXme sicle [pp. 273-293]Beyond the Planets: Early Nineteenth-Century Studies of Double Stars [pp. 295-309]Obituary: James Sterling Wilkie: 1906-1982 [pp. 310-311]Book ReviewsHistory of Natural HistoryReview: untitled [p. 312]Review: untitled [pp. 312-313]Review: untitled [p. 313]Review: untitled [pp. 314-316]Review: untitled [pp. 316-318]Review: untitled [p. 318]Review: untitled [pp. 318-319]Review: untitled [pp. 319-320]Review: untitled [p. 321]Review: untitled [pp. 321-322]Review: untitled [p. 322]Review: untitled [pp. 322-323]Review: untitled [pp. 323-324]

History of TechnologyReview: untitled [pp. 324-325]Review: untitled [pp. 325-326]Review: untitled [pp. 326-327]Review: untitled [pp. 327-328]Review: untitled [p. 328]Review: untitled [p. 329]Review: untitled [pp. 329-330]Review: untitled [pp. 330-331]Review: untitled [p. 331]Review: untitled [p. 332]

Science StudiesReview: untitled [pp. 332-334]Review: untitled [pp. 334-335]Review: untitled [p. 335]Review: untitled [pp. 335-336]Review: untitled [pp. 336-337]

Books Received [pp. 338-340]The British Society for the History of Science: Report of Council for the Year 1983-4 [pp. 341-345]Back Matter [pp. 346-346]

kragh, helge - julius thomsen and classical thermochemistry

Documents