I wish to thank N. W. Fisher, D. H. Stapleton, I. Palley, and the referees, for helpful comments. The research for this paper was supported in part by the Deutscher Akademischer Austauschdienst.

¹ Kekulé, A., ‘Ueber die Constitution und die Metamorphosen der chemischen Verbindungen und über die chemische Natur des Kohlenstoffs’, Annalen, 1858, 106, 129–59CrossRefGoogle Scholar; Couper, A. S., ‘On a new chemical theory’, Philosophical magazine, 1858, 16, 104–16.Google Scholar

² Butlerov, A. M., ‘Einiges über die chemische Structur der Körper’, Zeitschrift für Chemie, 1861, 4, 549–60.Google Scholar

³ Hunsberger, I. M., ‘Theoretical chemistry in Russia’, Journal of chemical education, 1954, 31, 504–14CrossRefGoogle Scholar; Joravsky, D., ‘Soviet views on the history of science’, Isis, 1955, 46, 3–13CrossRefGoogle Scholar; Rabkin, Y. M., ‘Trends and forces in the Soviet history of chemistry’, Isis, 1976, 67, 257–73CrossRefGoogle Scholar; and Graham, L. R., Science and philosophy in the Soviet Union, New York, 1972, especially chapter VIII.Google Scholar

⁴ Although I regard the intent of Couper's 1858 paper as virtually the same as Kekulé's, I will not consider here the question of Couper's contributions, since Kekulé's paper was both slightly earlier and much more influential. As for the roles of Edward Frankland and Hermann Kolbe, see Hartley, H., Studies in the history of chemistry, Oxford, 1971, pp. 206–20Google Scholar, and Russell, C. A.'s masterly summary in his History of valency, Leicester, 1971, pp. 108–34.Google Scholar

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¹⁰ That structural chemistry represents a ‘Verschmelzung’ of radicals and types is a cliché at least as old as 1859; Kekulé, , Lehrbuch der organischen Chemie, 2 vols., Erlangen, 1861–1866, i, 89Google Scholar (fascicle issued 1859); Anschütz, R., August Kekulé, 2 vols., Berlin, 1929, ii, 939–40Google Scholar (the second volume contains all Kekulé's published papers, and I will normally cite this collection (hereafter simply ‘Anschütz’) rather than the original articles).

¹¹ Brooke, , ‘Wöhler's urea and its vital force?—a verdict from the chemists’, Ambix, 1968, 15, 84–114CrossRefGoogle Scholar; Fisher, , op. cit. (9), pp. 109–10.Google Scholar

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¹⁴ I say ‘almost’ because, as is well known, Odling managed to combine advocacy of this theory with a rather pronounced positivist tendency. See Russell, , op. cit. (4), pp. 54–5Google Scholar, and Brock, W. H. (ed.), The atomic debates, Leicester, 1967Google Scholar, passim. The quotation is from Williamson, A., ‘On the constitution of salts’, Journal of the Chemical Society, 1851, 4, 350–5(351).Google Scholar

¹⁵ Gerhardt, C., Traité de chimie organique, 4 vols., Paris, 1853–1856, iv, 629, 749, and passim.Google Scholar

¹⁶ Kekulé, , op. cit. (10), i, 94Google Scholar; Rocke, A. J., ‘Origins of the structural theory in organic chemistry’, University of Wisconsin-Madison PhD dissertation, 1975, pp. 274–5Google Scholar; Anschütz, , i, 158, 205Google Scholar; ii. 61–2, 67, 77, 81, 84n., 101. These ten citations specify material written by Kekulé during the years 1854–60. See also Russell, , op. cit. (4), pp. 142–4.Google Scholar

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¹⁹ Ibid., ii, 943–5.

²⁰ Ibid., pp. 67, 77.

²¹ Kekulé, , ‘l'eber die s.g. gepaarten Verbindungen und die Theorie der mehratomigen Radicale’, Annalen, 1857, 704, 129–50 (129)Google Scholar; Anschütz, , ii, 80–96 (80).Google Scholar

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²⁵ Anschütz, , ii, 203–4Google Scholar; Kekulé, ibid., i, 129–31, 174, 729–41 (1859–61).

²⁶ Kekulé, ibid., i, 153–7; cf. op. cit. (21), p. 91 (1857).Google Scholar

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³⁴ Ibid., pp. 52, 55–60, 63–6. Butlerov had presented these considerations to a meeting of the Société Chimique de Paris (17 February 1858) when Couper was present, but they were never published. See Jacques, J., ‘Butlerov, Couper et la Société Chimique de Paris’, Bulletin de la Société Chimique, 1953, pp. 528–30.Google Scholar

³⁵ Butlerov, , ‘Einiges über die chemische Structur der Körper’, Zeitschrift für Chemie, 1861, 4, 549–60.Google Scholar

³⁶ Ibid., pp. 550–1.

³⁷ Ibid., pp. 552–3.

³⁸ Butlerov, , op. cit. (33), p. 52Google Scholar; Kekulé, , op. cit. (1), p. 147n.Google Scholar

³⁹ Russell, , op. cit. (4), p. 146.Google Scholar

⁴⁰ ‘Die Art und Weise der gegenseitigen Bindung der Atome in einem zusammengesetzten Körper’, or ‘die Art und Weise, nach welchen [die Elemente] chemisch zusammenhängen’; Butlerov, , op. cit. (35), pp. 553–4Google Scholar. Russian translation by Butlerov, in op. cit. (5), i, 70Google Scholar; ‘raspredelenie deistviia srodstva’.

⁴¹ ‘Poriadok khimicheskogo vzaimodeistviia razlichnykh elementarnykh paev, resul'tatom kotorogo budet sushchestvovanie opredelennoi chastitsi’, cited in Bykov, , Istoriia organicheskoi khimii, Moscow, 1976, p. 33Google Scholar; cf. also idem, ‘Zabytye izdaniia lektsii A. M. Butlerova po khimii’, Trudy instituta istorü estestvoznaniia i tekhniki, 1954, 2, 67–90 (70ff.).Google Scholar

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⁴³ Butlerov, , ‘Ueber die verschiedenen Erklärungsweisen einiger Fälle von Isomerie’, Zeitschrift für Chemie, 1863, 2, 500–34 (503).Google Scholar

⁴⁴ Butlerov, , op. cit. (42, Lehrbuch), p. 52Google Scholar; op. cit. (35), p. 554.Google Scholar

⁴⁵ Butlerov, , op. cit. (35), p. 560Google Scholar. Bykov suggests that this disclaimer was due to Butlerov, 's ‘habitual modesty’Google Scholar; ‘Origin of the theory of chemical structure’, Journal of chemical education, 1962, 39, 220–4 (222).Google Scholar

⁴⁶ This point has been urged before by Hoijtink, G. J., ‘Butlerow's bijdrage tot de ontwikkeling van de structuur theorie in de organische chemie’, Chemisch weekblad, 1957, 53, 164–9Google Scholar; 1958, 54, 218.

⁴⁷ Butlerov, , op. cit. (43).Google Scholar

⁴⁸ Ibid., pp. 501, 506; op. cit. (42, Lehrbuch), pp. 36–7Google Scholar; ‘Ueber die systematische Anwendung des Princips der Atomigkeit zur Prognose von Isomerie und Metamerielällen’, Zeitschrift für Chemie, 1864, 7, 513–32.Google Scholar

⁴⁹ Butlerov, , op. cit. (43), pp. 502–5, 520.Google Scholar

⁵⁰ Ibid., pp. 505–9.

⁵¹ Cf. Butlerov, 's very similar interpretation of rational formulae: op. cit. (42, Lehrbuch), p. 37.Google Scholar

⁵² Butlerov, , op. cit. (43), p. 505.Google Scholar

⁵³ E.g., Kekulé, , op. cit. (10), i, 183ff.Google Scholar

⁵⁴ Butlerov, , op. cit. (43), p. 504n.Google Scholar

⁵⁵ Erlenmeyer, , ‘Hypothesen über chemische Isomerie und chemische Constitution’, Zeitschrift für Chemie, 1864, 7, 1–30 (10n.).Google Scholar

⁵⁶ Kekulé, , ‘Untersuchungen über organische Säuren’, Annalen, 1864, 130, 1–31 (12).CrossRefGoogle Scholar

⁵⁷ Kekulé, , op. cit. (10), ii, 245Google Scholar. This assertion by Kekulé has been disputed by Bykov and others. For documentation of his claim, see ibid., i, 164, 522–3; ii, 2n., 7.

⁵⁸ Ibid., pp. 245–7. Cf. Kekulé's similar statements on formulae, in his ‘Untersuchungen über aromatische Verbindungen’, Annalen, 1866, 137, 129–96 (156).Google Scholar

⁵⁹ Heintz, W., ‘Ueber die Aethyldiglycolamidsäure…’ Annalen, 1864, 132, 1–25(21–3).CrossRefGoogle Scholar

⁶⁰ Markovnikov, , ‘Zur Geschichte der Lehre über die chemische Structur’, Zeitschrift für Chemie, 1865, 8, 280–7.Google Scholar

⁶¹ Butlerov, , ‘Ueber die Derivate von Trimethylcarbinol…’ Annalen, 1867, 144, 1–32 (9–10n.).Google Scholar

⁶² Meyer, L., ‘Zum Abwehr’, Annalen, 1868, 145, 124–7.CrossRefGoogle Scholar

⁶³ Butlerov, , ‘Eine Antwort’, Annalen, 1868, 146, 260–3CrossRefGoogle Scholar, my emphasis. Bykov, G. V. has conceded that this note contains no priority claim for structure theory per se; Istoriia klassicheskoi teorii khimicheskogo stroeniia, Moscow, 1960, p. 284Google Scholar. For another similar discussion by Butlerov, see his op. cit. (42, Lehrbuch), pp. 75–8.Google Scholar

⁶⁴ Butlerov, , ‘Istoricheskii ocherk razvitiia khimii v poslednie 40 let’, in op. cit. (5), iii, 167–280 (272–8).Google Scholar

⁶⁵ Ibid., p. 277.

⁶⁶ Anschütz, , i, 147–8, 157–8, 554Google Scholar; ii, 80–1, 102, 939–43, 951.

⁶⁷ Wurtz, , ‘Discours préliminaire: histoire des doctrines chimiques depuis Lavoisier’Google Scholar, in idem (ed.), Dictionnaire de chimie pure et appliquée, Paris, 1868, i, pp. i–lxxxviGoogle Scholar; Ladenburg, Albert, Vorträge über die Entwicklungsgeschichte der Chemie in den letzten hundert Jahren, Brunswick, 1869Google Scholar, translated as Lectures on the history of the development of chemistry since the time of Lavoisier, Edinburgh, 1900Google Scholar; Kopp, Hermann, Die Entwickelung der Chemie in den neueren Zeit, Munich, 1873.Google Scholar

⁶⁸ Markovnikov, V., ‘Vospominaniia i cherty iz zhizni i deiatel'nosti A. M. Butlerova’, Zhurnal russkago fiziko-khimicheskago obshchestva, 1887, 19, supplement, pp. 69–96Google Scholar; Schorlemmer, Carl, The rise and development of organic chemistry, Manchester, 1879; revised edn., London, 1894Google Scholar. Markovnikov had progressed from a ‘weak Kekulé’ position in his 1864 essay, intended to counter the implicit ‘strong Kekulé’ claims of the Germans. In the light of later developments, Schorlemmer's position is ironic, as he was a Marxist seeking to apply dialectical analysis to the history of chemistry; he certainly does not seem to have recognized any dialectical materialism in Butlerov's chemistry. On the other hand, he shared the same home town (Darmstadt) and the same university education (Giessen) with Kekulé.

⁶⁹ Menshutkin, B. N., Khimiia i puti ee razvitiia, Moscow, 1937Google Scholar; Syrkin, la. K. and Diatkina, M. E., Khimicheskaia sviaz'i stroenie molekul, Moscow, 1946.Google Scholar

⁷⁰ Medvedev, Zhores, The rise and fall of T. D. Lysenko, New York, 1969, pp. 117–34Google Scholar; the quotation (p. 121) is by Bushinskii, V. P., in Nauka i zhizn’, 1948, 10, 36–9Google Scholar. See also Medvedev, , Soviet science, Oxford, 1978, p. 47Google Scholar; and Graham, Loren R., Science and philosophy in the Soviet Union, New York, 1972, passim.Google Scholar

⁷¹ Chelintsev, G. V., Ocherki po teorii organicheskoi khimii, Moscow, 1949Google Scholar; Tatevskii, V. M. and Shakhparanov, M. I., ‘Ob odnoi makhistskoi teorii v khimii i ee propagandistakh’, Voprosy filosofii, 1949, 3, 76–92Google Scholar; translated as ‘About a Machistic theory in chemistry and its propagandists’, Journal of chemical education, 1952, 29, 13–14Google Scholar. Graham deals with the Chelintsev episode in ibid., chapter VIII, and I follow his treatment closely.

⁷² Bykov's dissertation is entitled ‘Vozniknovenie i razvitie klassicheskoi teorii stroeniia organicheskikh soedinenii’, University of Moscow, 1950. For the Soviet literature and historiography on Butlerov, see n. 3, above, and the following works: Bykov, , op. cit. (63), pp. 265–306Google Scholar; idem, ‘Razrabotka v SSSR istorii teorii khimicheskogo stroeniia i nauchnogo naslediia A. M. Butlerova’, Voprosy istorii estestvoznaniia i tekhniki, 1962, 12, 165–9Google Scholar; idem, op. cit. (41, Istoriia organicheskoi khimii), pp. 40–6Google Scholar. For bibliographies of works by and about Butlerov, see also Gumilevskii, L., Aleksandr Mikhailovich Butlerov, 1828–1886, Moscow, 1952, pp. 331–4Google Scholar, and Kazanskii, B. A., Petrov, A. D., and Bykov, G. V., eds., A. M. Butlerov: Izbrannye raboty po organicheskoi khimii, Moscow, 1951, pp. 659–85Google Scholar. Perhaps the strongest Butlerov claim ever made was by Davydov, V. N., in a work characterized by truly intemperate chauvinism, Über die Entstehung der chemischen Strukturlehre, Berlin, 1957Google Scholar; as a single example, Davydov asserts (p. 45) that Dalton made no essential advance over Lomonosov's atomic theory!

⁷³ Kursanov, D. N. et al. , ‘K voprosu o sovremennom sostoianii teorii khimicheskogo stroeniia’, Uspekhi khimii, 1950, 19, 529–44Google Scholar; translated as ‘The present state of the chemical structure theory’, Journal of chemical education, 1952, 29, 2–13(2).Google Scholar

⁷⁴ Kazanskii, and Bykov, , ‘A. M. Butlerov i teoriia khimicheskogo stroeniia’Google Scholar, in Kazanskii, et al. , op. cit. (72), pp. 527–90Google Scholar; Chelintsev, , ‘O teorii khimicheskogo stroeniia A. M. Butlerova i ee novykh uspekhakh’, Zhurnal obshchei khimii, 1952, 22, 350–60.Google Scholar

⁷⁵ Graham, , op. cit. (70), p. 312.Google Scholar

⁷⁶ Kazanskii, and Bykov, , ‘K voprosu o sostoianii teorii khimicheskogo stroeniia v organicheskoi khimii’, Zhurnal obshchei khimii, 1953, 23, 168–76Google Scholar. This article was published in the same month (January) that the infamous ‘doctors' plot’ was announced, presaging a massive purge that was only derailed by Stalin's death two months later.

⁷⁷ Bykov, , op. cit. (41, Istoriia organicheskoi khimii), p. 44.Google Scholar

⁷⁸ W. V., and Farrar, K. R., ‘Faith and doubt: the theory of structure in organic chemistry’, Proceedings of the Chemical Society, 1959, pp. 285–90Google Scholar; Bykov, letter to editor, with rebuttal by the Farrars, ibid., 1960, pp. 210–11; Bykov, , op. cit. (41, Istoriia organicheskoi khimii), pp. 44–5Google Scholar, which verifies the intended Russian phrasing.

⁷⁹ Giua, M., Storia della chimica, Turin, 1946Google Scholar; Jacques, J., ‘La naissance de l'idée de structure chimique et les savants du XIX^e siècle’, University of Paris, 1956Google Scholar; Russell, , op. cit. (4)Google Scholar; Tanaka, M., ‘Einige methodologische Probleme des klassischen Begriffs der chemischen Struktur und dessen Übergang zum gegenwärtigen Begriff’, Japanese studies in the history of science, 1972, 11, 113–26Google Scholar. The works of H. M. Leicester (USA) and D. F. Larder (Canada) are discussed below.

⁸⁰ Ihde, A. J., Development of modern chemistry. New York, 1964Google Scholar; Partington, J. R., A history of chemistry, iv, London, 1964.CrossRefGoogle Scholar

⁸¹ Leicester, , op. cit. (32)Google Scholar; idem, ‘Kekulé, Butlerov, Markovnikov: Controversies on chemical structure from 1860 to 1870’, in Benfey, O. T. (ed), Kekulé centennial, Washington, DC, 1966, pp. 13–23.CrossRefGoogle Scholar

⁸² I interpret the 1940 biography as ‘weak Kekulé’, though it certainly shades toward being ‘weak Butlerov’. Leicester, 's Historical background of chemistry. New York, 1956Google Scholar, is distinctly ‘weak Kekulé’, while his ‘Contributions of Butlerov to the development of structural theory’, Journal of chemical education, 1959, 36, 328–9Google Scholar, is clearly ‘weak Butlerov’.

⁸³ Larder, D. F., op. cit. (31).Google Scholar

⁸⁴ Bykov, , op. cit. (63), pp. 66, 85–6, 121Google Scholar; op. cit. (45), p. 221Google Scholar; op. cit. (32), p. 622.Google Scholar

⁸⁵ Larder, , op.cit. (31), pp. 32–3, 38–9, 43–4.Google Scholar

⁸⁶ See n. 31, above.

⁸⁷ Bykov, , op. cit. (63), pp. 34, 121Google Scholar; idem, A.M. Butlerov, Moscow, 1961, pp. 55–6Google Scholar; idem, August Kekule, Moscow, 1964, pp. 40, 156.Google Scholar

⁸⁸ Kekulé, , op.cit. (10), i, 162n., 174nGoogle Scholar; Butlerov, , ‘Ueber die Verwandtschaft der mehraffinen Atome’, Zeitschrift für Chemie, 1862, 5, 297–304(299)Google Scholar; see also his op. cit. (43), p. 501.Google Scholar

⁸⁹ Larder, , op. cit. (31), pp. 31–3, 36–9.Google Scholar

⁹⁰ Anschütz, , i, 103–9 (1858), 656–8 (1872)Google Scholar; Kekulé, , op. cit. (10), i, 134–58, 522–4Google Scholar; Butlerov, , op. cit. (88)Google Scholar. One referee has suggested in support of Larder that Butlerov's definition of structure as ‘die Reihenfolge der Wechselwirkung’ or ‘poriadok vzaimodeistviia’ of the atoms in a molecule introduced a time dimension, and hence implies a dynamical view. This depends on one's interpretation of what Butlerov might have meant by ‘Reihenfolge’ or ‘poriadok’ (order or sequence). I suggest that Butlerov used such words as epistemologically cautious circumlocutions for ‘arrangement’, which had too physical a connotation. This seems to me to be clear from the context. For ‘poriadok’ Butlerov also used the word ‘raspredelenie’ (distribution’), which has no temporal connotation (see p. 37 above). Furthermore, the Russian historians Bykov, Kazanskii, and S. N. Vinogradov have all translated ‘poriadok’ into English as ‘sequence or arrangement’ (my emphasis); see Kazanskii, and Bykov, in their (eds.), Centenary of the theory of chemical structure, Moscow, 1961, p. 5Google Scholar; Vinogradov, S. N., ‘Chemistry at Kazan University in the nineteenth century: a case history of intellectual lineage’, Isis, 1965, 56, 168–73(171).CrossRefGoogle Scholar

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⁹² Bykov, , op. cit. (72, ‘Razrabotka’); op. cit. (45), pp. 222–3Google Scholar; op. cit. (32), p. 622Google Scholar. See also Gumilevskii, , op. cit. (72), p. 109.Google Scholar

⁹³ Leicester, , op. cit. (82).Google Scholar

⁹⁴ Kekulé, , op. cit. (10), i, 174, 183–92Google Scholar; cf. Butlerov's very similar treatment of lactic acid, op. cit. (42, Lehrbuch), pp. 47–8.Google Scholar

⁹⁵ Bykov, , ‘A. M. Butlerov i angliiskie khimiki’, Voprosy istorii estestvoznaniia i tekhniki, 1956, 1, 286–9Google Scholar; Larder, , op. cit. (31), p. 42.Google Scholar

⁹⁶ Brown, Crum, ‘On the theory of chemical combination’, University of Edinburgh MD thesis, 1861Google Scholar; idem, op. cit. (31).

⁹⁷ Brown, Crum, ‘On the use of graphic representations of chemical formulae’, Proceedings of the Royal Society of Edinburgh, 1865, 5, 429–31.CrossRefGoogle Scholar

⁹⁸ To Kekulé he wrote: ‘I have always considered myself as, in a sense, your disciple, so many of my ideas being derived, directly or indirectly from you’ (18 February 1869, in August Kekulé-Zimmer, Institut für Organische Chemie, Technische Hochschule, Darmstadt; I thank Professor K. Hafner for permission to use this collection in May 1975). Crum Brown's corresponding letter to Butlerov is a simple request for a recommendation (5 December 1868, Russian translation in Pogodin, S. A. et al. , eds., A. M. Butlerov, Nauchnaiia i pedagogicheskaiia deiatel ‘nost’, sbornik dokumentov, Moscow, 1961, p. 394Google Scholar; I thank Professor Bykov for sending me a transcription of the original French-language letter).

⁹⁹ Brown, Crum, op. cit. (96), p. 23Google Scholar; op. cit. (31), pp. 714–15, 718.Google Scholar

¹⁰⁰ Bykov, , op. cit. (72, dissertation)Google Scholar. An English resumé was published as ‘Rise and development of the classical theory of chemical structure’, Actes du VIII^e Congrès International d'Histoire des Sciences, Milan, 1958, ii, 573–6; Kursanov, D. N. et al. , ‘The present state of the chemical structural theory’, Journal of chemical education, 1952, 29, 2–13CrossRefGoogle Scholar (originally published in Uspekhi Khimii, 1950, 19, 529–44)Google Scholar; Leicester, , op. cit. (82), p. 328Google Scholar; Bykov, , op. cit. (63), pp. 85, 90, 118, 130, 265Google Scholar; idem, op. cit. (72, ‘Razrabotka’), pp. 165, 168Google Scholar; idem, op. cit. (45), pp. 220, 222Google Scholar; Leicester, , op. cit. (81, ‘Kekulé, Butlerov, Markovnikov’) pp. 16–17Google Scholar; Larder, , op. cit. (31), p. 47Google Scholar; Bykov, , op. cit. (41, Istoriia organicheskoi khimii), pp. 33–4.Google Scholar

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¹⁰² Brooke, , op. cit. (9, ‘Organic synthesis’), pp. 364–5Google Scholar; idem, op. cit. (11).

¹⁰³ Levere, T. H., op. cit. (28)Google Scholar; idem, Affinity and matter, Oxford, 1971, pp. 151–9, 183–4Google Scholar; Knight, D. M., The transcendental part of chemistry, Folkestone, 1978, pp. 186–209Google Scholar; Farrar, W. V., ‘Dalton and structural chemistry’, in Cardwell, D. S. L. (ed.), John Dalton and the progress of science, Manchester, 1968, pp. 293–4.Google Scholar

¹⁰⁴ Laurent, , Chemical method (tr. by Olding, W.), London, 1855, p. 268Google Scholar; Levere, ibid. (Affinity and matter), p. 184.

¹⁰⁵ Kazanskii, and Bykov, , op. cit. (74), p. 544Google Scholar; Bykov, , op. cit. (87, Kekule), pp. 45–6Google Scholar. For citations documenting Kekulé's departure from Gerhardt's anti-structuralism, see n. 16 above.

¹⁰⁶ Kazanskii and Bykov, ibid., p. 581; Bykov, , op. cit. (87, Butlerov), p. 100Google Scholar; op. cit. (87, Kekule), p. 171Google Scholar; op. cit. (32), p. 621; op. cit. (45), p. 221Google Scholar; op. cit. (41, Istoriia organicheskoi khimii), p. 27.Google Scholar

¹⁰⁷ Kekulé, , ‘Ueber einige organische Säuren’, Zeitschrift für Chemie, 1861, 4, 613–25Google Scholar (621–2); Anschütz, , ii, 232.Google Scholar

¹⁰⁸ It is simply not true, as has been often stated (e.g., Kazanskii, and Bykov, , op. cit. (74), p. 581)Google Scholar that type formulae disappeared completely from Kekulé's papers between 1861 and 1863. In this period Kekulé published thirteen papers. In eight he used type formulae largely or exclusively, and in three he used largely empirical formulae, but at least one type formula. The only papers that contained no types were a brief note on tin ethyl, and the above oral report.

¹⁰⁹ Markovnikov, , op. cit. (60), p. 284Google Scholar; Bykov, , op. cit. (32), p. 623Google Scholar; Leicester, , op. cit. (81, ‘Kekulé, Butlerov, Markovnikov’), p. 17.Google Scholar

¹¹⁰ Kekulé, , op. cit. (10), ii, 1–240, 241–480.Google Scholar

¹¹¹ Kekulé flirted with the double-bond idea from 1858 onwards, and used it explicitly in his benzene theory (1865). He used the ‘gap’ concept to explain the structure of the unsaturated diacids; Anschütz, , ii, 294–8Google Scholar (1862–4). He was perhaps led to this idea because, in the absence of stereochemical considerations, formulae using double bonds could not explain the observed cases of isomerism.

¹¹² Erlenmeyer, , ‘Bemerkungen…’ Zeitschrift für Chemie, 1863, 6, 21–22Google Scholar; Butlerov, , op. cit. (43)Google Scholar; Brown, Crum, op. cit. (31), p. 718.Google Scholar

¹¹³ Kekulé, , op. cit. (10), ii, 139.Google Scholar

¹¹⁴ Brown, Crum, op. cit. (97).Google Scholar

¹¹⁵ Fisher, , ‘Wislicenus and lactic acid’, in Ramsay, O. B. (ed.), van't Hoff-Le Bel centennial, Washington, DC, 1975, pp. 33–54 (49)CrossRefGoogle Scholar. Butlerov, , too, admitted the possibility of three trichloroethanes: op. cit. (42, Lehrbuch), pp. 48–50.Google Scholar

¹¹⁶ Brown, Crum, op. cit. (31), p. 715Google Scholar; Kekulé, , op. cit. (10), i, 188.Google Scholar

¹¹⁷ Crum Brown, ibid., pp. 714–5.

¹¹⁸ Kekulé, , op. cit. (10), i, 187–92Google Scholar; ii, 139–40.

¹¹⁹ Ibid., i, 556, 676, 679; ii, 95–6, 247–8, 408–9.

¹²⁰ Ibid., i, 177n.; ii, 95–6, 272. In all three cases, Kekulé could not decide between structures involving what we would call nitrile or amino groups.

¹²¹ Anschütz, , ii, 118.Google Scholar

¹²² Kekulé, , op. cit. (10), i, 95Google Scholar; Bykov, , op. cit. (63), p. 31Google Scholar; op. cit. (87, Kekulé), p. 54.Google Scholar

¹²³ Butlerov, , op. cit. (43), p. 504Google Scholar; op. cit. (42, Lehrbuch), pp. 50–1.Google Scholar

¹²⁴ In a series of letters to A. von Planta (especially that of 9 February 1856) Kekulé stressed his love of chemical theory over practice. On 13 June 1860 Kekulé wrote to Erlenmeyer, who had helped correct proof sheets for Kekulé's textbook and had complained of certain obscure passages. Kekulé explained that such ambiguities were intentional, and were designed to reserve priority for ideas that he intended to develop in more detail in the future. These letters are preserved in the August Kekulé-Zimmer, Darmstadt, , loc. cit. (98).Google Scholar

¹²⁵ von Baeyer, A., Gesammelte Werke, Brunswick, 1905, i, xv.Google Scholar

¹²⁶ Anschütz, , ii, 940–1.Google Scholar