ambix, Vol. 61 No. 3, August, 2014, 257–278

Pedagogical Progeniture or Tactical Translation? George Fordyce’s Additions and Modifications to William Cullen’s Philosophical Chemistry—Part II Georgette Taylor University College London

This paper compares the affinity theories and the associated affinity diagrams of William Cullen (1710–1790) and George Fordyce (1736–1802), exploring in particular one episode that took place during the brief hiatus between Fordyce’s student years at Edinburgh University and the start of his own pedagogical career in London. This investigation complements that contained in Part I of this paper, which compared the chemistry courses given by Cullen and Fordyce, demonstrating that the knowledge originally imparted to Fordyce by Cullen in his Edinburgh lectures was augmented and translated by Fordyce for his own pedagogical purposes. Part II offers greater insight into the flow of knowledge between Fordyce and Cullen. Their correspondence suggests that the relationship between master and student transmuted into something more complicated after Fordyce left Edinburgh, while the model of knowledge transmission between the two can be seen to be more collaborative than might be expected.

George Fordyce: a cosmopolitan chemist The name of George Fordyce (1736–1802) is rarely encountered today, yet many researchers into eighteenth-century science will have encountered him fleetingly in sometimes surprising contexts, as an acknowledged expert on various branches of science in eighteenth-century London. Although Fordyce learned his chemistry from William Cullen while studying medicine at Edinburgh University, it was in London that he would launch his own career as a teacher of chemistry, eventually developing a theory of elective affinity which differed from that of his former

© Society for the History of Alchemy and Chemistry 2014

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teacher in several respects.1 In London, Fordyce established himself at the heart of a scientific and literary community upon which he seems to have exerted considerable influence, even if the traces of that influence are now little known. Fordyce’s initial choice of career seems to have disappointed his relations. According to his obituary in the Gentleman’s Magazine, when he made known his intention to fix himself as a teacher and practitioner of medicine to his relations, they highly disapproved of it, as the whole of his patrimony had been expended upon his education.2

Fordyce was to eventually prove this pessimism to have been misplaced. Almost from his first arrival in London, he seems to have been a ubiquitous member of any scientific club, society or meeting on science, fraternising with John and William Hunter (the latter nominating him as Trustee of his estate), Joseph Banks, Charles Blagden, James Keir, Daniel Solander, and Captain Cook, amongst others.3 He published a number of papers in the Philosophical Transactions, and in 1776 was elected a Fellow of the Royal Society.4 His Elements of Agriculture, first published in 1765, was copiously cited, as were his works on heat.5 In 1785, Joseph Black appears to have written to James Lind asking for news of Fordyce’s experiments on the weight of heat, and in 1787 the topic arose again in a letter from Black to Thomas Beddoes.6 Jeremy Bentham seems to have attended Fordyce’s lectures in August and September 1769,7 later claiming, “I worshipped Dr Fordyce on account of his chemical knowledge. He knew everything that was then known.”8 1

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On Fordyce’s education and early career, see Georgette Taylor, “Pedagogical Progeniture or Tactical Translation? George Fordyce’s Additions and Modifications to William Cullen’s Philosophical Chemistry—Part I,” Ambix 61 no. 1 (2014): 48–66 (hereafter “Part I”). Anon., “Obituary, with Anecdotes of Remarkable Persons,” Gentleman’s Magazine: and Historical Chronicle, for the Year 1782 72 (1802): 584–92, on 588. Jacob W. Gruber, “Hunter, John (1728–1793),” Oxford Dictionary of National Biography (Oxford: Oxford University Press, 2004); online edn, May 2010: http://www.oxforddnb.com/view/article/14220 (accessed 15 June 2014); Will of William Hunter, 4 April 1783, P.R.O. Prob11/1102. George Fordyce, “Of the Light Produced by Inflammation. By George Fordyce, M.D. F.R.S,” Philosophical Transactions of the Royal Society of London (hereafter Phil. Trans.) 66 (1776): 504–08; George Fordyce, “A New Method of Assaying Copper Ores. By George Fordyce, M.D. F.R.S,” Phil. Trans. 70 (1780): 30–41; George Fordyce, “An Account of Some Experiments on the Loss of Weight in Bodies on Being Melted or Heated. In a Letter from George Fordyce, M.D. F.R.S. To Sir Joseph Banks, Bart. P.R.S,” Phil. Trans. 75 (1785): 361–65; George Fordyce, “An Account of an Experiment on Heat. By George Fordyce, M.D. F.R.S. In a Letter to Sir Joseph Banks, Bart. P. R. S,” Phil. Trans. 77 (1787): 310–17, George Fordyce, “The Croonian Lecture on Muscular Motion. By George Fordyce, M.D. F.R.S,” Phil. Trans. 78 (1788): 23–36; George Fordyce, “On the Cause of the Additional Weight Which Metals Acquire by Being Calcined. In a Letter from George Fordyce, M.D. F.R.S. To Sir Joseph Banks, Bart. P. R. S,” Phil. Trans. 82 (1792): 374–82, George Fordyce, “Account of a New Pendulum. By George Fordyce, M.D. F.R.S.; Being the Bakerian Lecture,” Phil. Trans. 84 (1794): 2–20. George Fordyce, Elements of Agriculture (Edinburgh: [1765]). See also note 62. Black’s letter to Lind does not survive, but it is clear from Lind to Black, 27 March 1785, that he wrote requesting more information. The 1787 letter exists only as a draft: Black to Beddoes 24 November 1787, Correspondence of Joseph Black, ed. R. G. W. Anderson and J. Jones (Farnham: Ashgate, 2012), vol. 2, 805 and 925. Fordyce’s joint experiments with Charles Blagden to discover the effects of heat on the human body were of sufficient interest to be reprinted in the Encyclopaedia Britannica. See “Heat,” Encyclopaedia Britannica, 3rd ed. (Edinburgh: A. Bell and C. MacFarquar, 1790–1798), vol. VIII, 355 See Jeremy Bentham, “Commonplace Book” (1769), British Library, London, Add. MS 33564, fol. 55 ff; Taylor, “Part I,” on 51. Jeremy Bentham, The Works of Jeremy Bentham, published under the superintendence of his Executor, John Bowring ed., 11 vols. (Edinburgh: Simkin, Marshall & Co, 1838–1843), vol. 10, 571.

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Bentham’s brother in fact married Fordyce’s daughter, and much later Fordyce advised Bentham on the flow of air through his Panopticon.9 Fordyce also advised during Vincenzo Lunardi’s balloon ascent of 1784 (and indeed was responsible for supplying the inflammable air for the balloon), taught William Congreve chemistry, and assisted in the improvement of gunpowder manufacture. His daughter claims that Fordyce was responsible for the idea that painting wood with “oil of tar” (something akin to creosote) would assist in its preservation.10 Perhaps more surprising are his links to the literary luminaries of eighteenth-century London society. Fordyce was elected to Goldsmith’s Literary Club in 1774 alongside Charles James Fox and Sir Charles Bunbury, and socialised with Samuel Johnson, David Garrick, and Joshua Reynolds, amongst others.11 He was also, it seems, a trusted friend of Mary Wollstonecraft, to whose deathbed he was called at her request, in spite of his lack of obstetric experience.12 Fordyce, then, was at the heart of scientific London for much of the second half of the eighteenth century, as a lecturer, physician, and acknowledged expert on chemistry. Some clues as to why Fordyce was so well regarded have already been discussed in Part I. Part II will illuminate the matter through an examination of his ideas on affinity, as articulated in an exchange of correspondence with his old lecturer, William Cullen, and later in his lectures to his own students.

Representing affinity For much of the eighteenth century, affinity theory provided chemists with a coherent framework for the explanation and, in many cases, prediction of chemical behaviour when a small number of simple substances (simple in the sense that the chemists of the time were unable to decompose them13) were mixed together. The

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Jeremy Bentham, Panopticon: Or, the Inspection-House. Containing the Idea of a New Principle of Construction Applicable to Any Sort of Establishment, in Which Persons … Are to Be Kept … And in Particular to PenitentiaryHouses, Prisons, … In a Series of Letters, Written In … 1787 (Dublin: Thomas Byrne, 1791), 308, 311–312. Anon. Lunardi’s Grand Aerostatic Voyage through the Air, Containing a Complete and Circumstantial Account of the Grand Aerial Flight Made by That Enterprising Foreigner, in His Air Balloon, on September 15, 1784 (London: Printed for J. Bew; J. Murray; Richardson and Urquhart; and R. Ryan; and sold by all the town and country booksellers, 1784), 3. See also the letter from James Trail to Jeremy Bentham giving an account of this episode in Bentham, Works of Jeremy Bentham, vol. 10. On his work with Congreve, see Simon Werrett, “William Congreve’s Rational Rockets,” Notes and Records of the Royal Society 63 (2009): 35–56; Maria Bentham, “Memoir on the Various Methods Adopted and Proposed for the Preservation of Timber,” Mechanic’s Magazine No. 1415 (21 September 1850), 224–228, at 224. Unknown, ed., The Miscellaneous Works of Oliver Goldsmith, M.B.: A New Edition, in Six Volumes, to Which Is Prefixed, Some Account of His Life and Writings (New York: William Durell and Co., 1809), 73–74. Also Noel G. Coley, “George Fordyce MD FRS (1736–1802): Physician-Chemist and Eccentric,” Notes and Records of the Royal Society of London 55 (2001): 395–409. William Godwin, Memoirs of the Author of A Vindication of the Rights of Woman (London: Printed for J. Johnston, 1798), 72, 178. Wollestonecraft died giving birth to a daughter, later to become Mary Shelley. In his 1766 lectures, Cullen described ‘simple bodies’ as “such whose parts are all of the same kind, but this is only a relative term, & signifies that it is beyond our art to separate them into more sorts; for it is dubious if we know any matter truly simple.” William Cullen, “Notes Taken by Charles Blagden from Lectures on Chemistry 1765–1766” (1766), MS 1922, Blagden Papers, Wellcome Library, London, Lecture 12.

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classic example of affinity theory in action was the recovery of a metal from solution in acid by the simple expedient of substituting another metal (or alkali salt) with which the acid concerned had a greater chemical affinity. The original metal (or a form of it) would be precipitated out of the solution, while the new substance was itself dissolved. In William Cullen’s hands, however, affinity also served to explain more complex scenarios, such as the mixture of compound substances.14 At some point between 1748 and the late 1750s, Cullen began to introduce his students to a form of ‘equation’—cross diagrams in which he endeavoured to show how the constituent parts of two compound substances would behave when mixed together (see Figure 1 for an example from the 1760s).15 These effectively compared the different affinities that would act in such a mixture to produce what he called “double elective attractions,” where the compound substances, on being mixed together, would each be decomposed to produce new compounds. The diagrams, it seems, were for the most part intended to be explanatory or illustrative; Cullen emphasised that as affinities were not exactly quantifiable, the exact result of many of these kinds of mixtures could not be predicted without recourse to experiment. A set of notes dating from 1757 indicates that he did, however, suggest a general rule of thumb: in order for a double elective attraction one of the parts of each of the mixts must have a stronger attraction wt one of the parts in the other mixts than wt that it is at present combined wt as is evident by the Experiment.16

This rule of thumb, applied to the diagrams, broadly implies that in those cases where arrows or ‘darts’ can be drawn (from a glance at an affinity table) to form a cross shape, those double elective attractions will proceed. Cullen’s cross diagrams were extremely influential, in spite of the fact that they were not ‘published,’ at least in the sense in which the term is used now, during his lifetime. Nevertheless, they undoubtedly came to be known to the outside world through his students. Joseph Black adopted similar diagrams in his teaching,17 and several of Cullen’s other students also used them in their pedagogy. Duncan has noted that the double elective attraction diagrams presented by Torbern Bergman

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Cullen explained compound substances as being “those [bodies] whose parts are manifestly Different, either in form or matter, … the latter of these only is the subject of Ch[emistr]y.” Cullen, “Notes Taken by Charles Blagden,” Lecture 12. Maurice Crosland lists lecture notes from as early as 1756/7 (in a manuscript held at Aberdeen University) that contain these diagrams: Crosland, “The Use of Diagrams as Chemical ‘Equations’ in the Lecture Notes of William Cullen and Joseph Black,” Annals of Science 15 (1959): 75–90. There are also notes from 1757 which include these kinds of diagrams: William Cullen, “Lectures on Chemistry” (n.d. [1757/8]), MS 2, Cullen Papers, Library of the Royal College of Physicians Edinburgh, Edinburgh. William Cullen, “Rough Notes Taken by David Carmichael from Chemistry Lectures” (1757), MS 12, Cullen Papers, Library of the Royal College of Physicians of Edinburgh, Edinburgh, fol. 41. See, for example, Thomas Cochrane, Notes from Dr. Black’s Lectures on Chemistry 1767/8, ed. Douglas McKie (Wilmslow: Imperial Chemical Industries Limited, 1966), 59–60.

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figure 1 A page from Fordyce’s 1759 letter showing his diagrams and some of his elective attraction algebra. George Fordyce, “On Compound Attractions” (1759), Glasgow University Library, MS Cullen 89. By kind permission of Glasgow University Library, Special Collections.

later in the century bear a strong resemblance to Cullen’s, and it is highly likely that Bergman heard of them through Cullen’s students.18 Throughout all the years of his chemistry teaching, Cullen spent a number of consecutive lectures talking his students through the columns of an affinity table and commenting on their contents. According to the earliest sets of notes, dating from 18

Torbern Bergman, “Disquisito De Attractionibus Electivis,” Nova Acta Regiae Societatis Scientiarum Upsaliensis 2 (1775): 161–250; Torbern Bergman, A Dissertation on Elective Attractions, trans. [Thomas Beddoes?] (1785; reprint, with an introduction by A. M. Duncan, London: Frank Cass & Co. Ltd., 1970). See also, R. Passmore, A. Doig, J. P. S. Ferguson, and I. A. Milne, eds., William Cullen and the Eighteenth Century Medical World (Edinburgh: Edinburgh University Press, 1993), 32.

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1748 to 1750, he used Étienne Geoffroy’s original affinity table of 1718. In later lectures he also referred freely to the columns contained in William Lewis’s tables, comparing them with those of Geoffroy, and where necessary correcting both.19 There is also evidence that Cullen printed his own table for students from the late 1750s.20 A copy of a printed table of fifteen columns survives in the archives of the National Library of Wales, and it is possible that this was the table sold to students.21 Later lectures include a much enlarged and amended table of Cullen’s devising, which was apparently pinned up in order to be copied down by the students.22 Indeed, in the Wellcome Library’s set of 1766 lecture notes, mentioned earlier, we find a comment from the student note-taker, Charles Blagden: “to explain the subsequent Experiments, a portion of a Table of Elective Attractions was fixed up; but this being in almost every book of Ch[emistr]y is not worth repeating here.”23 Perhaps this was why Blagden signed up for a second chemistry course the following year. By 1766, Blagden was correct in his claim that affinity tables routinely appeared in any publication on chemistry worthy of the name, although at that date no textbook contained so large or comprehensive a table as Cullen was then presenting in his lectures. When Cullen began his lectures at Glasgow, no affinity table had yet been published in Britain. By the final year of his chemistry lectures at Edinburgh, Cullen had been teaching affinity theory as a general principle of the discipline for eighteen years. Many of his early students had themselves become lecturers, and they too taught their students to use affinity tables, and wrote the very textbooks that thrust affinity before an even larger audience.

Fordyce’s affinity theory Historians are fortunate that so much material survives in archives in Europe and America relating to Cullen’s life and work. This includes correspondence that can shed light on his relationships with his contemporaries and, of course, with some of his students. This material also offers the opportunity to examine the dynamics of knowledge transfer between master and student. 19

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William Lewis, The New Dispensatory: Containing I. The Theory and Practice of Pharmacy. II. A Distribution of Medicinal Simples, According to Their Virtues and Sensible Qualities; the Description, Use, and Dose of Each Article. III. A Full Translation of the London and Edinburgh Pharmacopoeias, with the Use, Dose &C. Of the Several Medicines. IV. Directions for Extemporaneous Prescription; with a Select Number of Elegant Forms. V. A Collection of Cheap Remedies for the Use of the Poor. The Whole Interspersed with Practical Cautions and O Observations. Intended as a Correction, and Improvement of Quincy (London: J. Nourse, 1753). See Cullen, “Rough Notes Taken by David Carmichael.” William Cullen, “Draft Letter to George Fordyce” (1759), MS 90, Cullen Papers, Glasgow University Library, Glasgow. William Cullen, “Dr Cullen’s Table of Elective Attractions” (n.d. [1750s?]), NLW MS 2568E, National Library of Wales, Aberystwyth. This table includes a column for fixed air, which would date it to around 1757–1759. For an example of an affinity table from one of Cullen’s lectures, see the front cover of Ambix 61, no. 1 (2014). This example is taken from William Cullen, “Notes Taken from Lectures on Chemistry” (n.d. [1760s]), MS/MSL/79a-c, Medical Society of London, Wellcome Library, London, fol. 79a. A further example can be found in William Cullen, “Notes Taken by Will Falconer from Chemistry Lectures” (1765), MS 1921, Wellcome Library, London. Cullen, “Notes Taken by Charles Blagden,” lecture 22.

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Records survive of a fascinating exchange between Cullen and the newly liberated Fordyce that opens a window allowing us to peer into Cullen’s study on 4 October 1759. Shortly before this date, Cullen had received a letter from Fordyce enclosing a paper that he optimistically suggested he might send to the Royal Society, hoping for publication. In it, Fordyce explained: I have been intending it every post these six months as I expected to have finished it then but various interruptions and a number of new experiments that occurr’d in order to satisfy myself thoroughly that the theory I had laid down was true in practice has prevented me till now. It is you see an attempt to show in what cases Double Elective Attractions take place likewise to show what combinations will take place when three or more compounds are mixt. I propose to give it in to the Royal society but would not take any measures for that end till I first consulted you.24

He continues, I proposed at the same time to have given in a table of Elective attractions but as I heard you have published one I have given over making experiments till I see it.

We come to the crux of the matter a few lines further on: I have done nothing else in Chymistry since I left Ed[inbu]r[gh] except some triffles for other people such as enamelling some stone for the duke of Argyle and giving directions for some furnaces. I should not have even meddled so for contrary to your advice but that something of that kind would please my uncles and furnish me with a pretence for being a Candidate for the Royal Society of which they want I should be a member.

Fordyce had a formidable collection of uncles—according to Jeremy Bentham, these numbered twenty: a banker, a professor of philosophy, a presbyterian divine and two physicians amongst them.25 As Fordyce was an only child himself, and indeed (as every near-contemporaneous biographical account of his life was keen to emphasise) born after the death of his father, he would presumably have felt a fairly hefty weight of expectation, and his letter to Cullen certainly seems to testify to this.26 There was certainly ample cause for the twenty uncles to have been proud of their nephew by the end of his career, but at this early stage the question was moot.27 The reference to the Duke of Argyll is, however, telling: this gentleman was one of the most powerful and wealthy men in Scotland, but also an active

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George Fordyce, “Five Letters to William Cullen” (1759–1774), MS 180, Cullen Papers, Glasgow University Library, Glasgow, First letter, 1759. Bentham, The Works of Jeremy Bentham, vol. 10, 184; Coley, “George Fordyce MD FRS (1736–1802).” See, for instance, The Annual Register, or a View of the History, Politics and Literature, for the Year 1802 (London: W. Otridge and Son; Clarks and Son; T. Hurst; E. Crosby; J. Bell; R. Faulder; Cuthell and Martin; Ogilvy and Son; R. Lea; J. Nunn; J. Walker; Lackington, Allen and Co; E. Jeffery; Vernor and Hood; J. Asperne; and Wynne and Scholey, 1803), 509. Fordyce’s uncle, James Fordyce, would probably not have approved his friendship with Wollstonecraft, whose A Vindication of the Rights of Woman castigated his views as expressed in his 1766 Sermons to Young Women. See Mary Wollstonecraft, A Vindication of the Rights of Woman: With strictures on political and moral subjects (London: Printed for J. Johnson, 1796), 206–214.

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improver with a strong interest in chemistry.28 Perhaps through the good offices of his uncles, at this early stage of his career Fordyce was already possessed of influential friends. The draft paper that accompanied the letter is held at Glasgow University Library. Misdescribed in the library catalogue, this has so far been overlooked by historians.29 It is a somewhat tortuous piece of work, which attempts to remove all doubt from what Cullen had called “double elective attractions” and Fordyce called “compound affinities” by proposing the use of a kind of algebraic comparison of the affinities between pairs of substances. It is clear that Fordyce hoped to be able to place the chemistry of complex combinations on a truly a priori footing, offering a rule of thumb that would enable future chemists to predict the results of mixtures of four or even six substances without the need for messy and time-consuming experiment. It is illuminating to examine Fordyce’s paper alongside Cullen’s own lecture notes.30 As noted above, Cullen had offered his rule of thumb which would enable chemists to tentatively predict the result of at least a proportion of the possible complex mixtures. Fordyce’s paper actually restates Cullen’s rule of thumb: It was found afterwards that several other menstruums could be separated from their solvends by joining two compounds and this was called double Elective attractions. There were commonly said to be four cases in which this would happen and in all these cases setting the substances combined together on the same side, one substance on each side attracts another on the other side stronger than the substance it is combined with.31

Having restated Cullen’s rule, Fordyce rejected it in favour of his own new law based on a comparison of the various affinities in opposition. In the first instance, he reduced all the possible results of combinations of four substances to four general cases, using diagrams similar to those presented to his students in 1757 by Cullen (Figure 1).32 Fordyce sought to use them slightly differently, however. He classed each substance as either menstruum or solvend: the menstruum usually (but not always) being the liquid body, and the solvend the (usually) solid substance to be dissolved therein. Fordyce used an affinity table, which listed affinities in order of strength from the strongest to the weakest, to work out which menstruum was strongest with regard to each solvend, and vice versa, thus enabling him to list the affinities at work in his mixture in order of strength. So, for example, in a mixture of nitrous acid, vitriolic acid, fixed vegetable alkali, and silver (which he used for both his first and second examples), the column for fixed vegetable alkali—a solvend—showed 28

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Roger Emerson, “The Scientific Interests of Archibald Campbell, 1st Earl of Ilay and 3rd Duke of Argyll (1682– 1761),” Annals of Science 59 (2002): 21–56. George Fordyce, “On Compound Elective Attractions” (1759), MS Cullen 89, Cullen Papers, Glasgow University Library, Glasgow. Two sets of notes on Cullen’s lectures, dated from 1757/8, held by the Royal College of Physicians in Edinburgh, correspond most closely to the date of these communications: one apparently being a ‘rough draft’ version of the other. Cullen, “Rough Notes Taken by David Carmichael”; Cullen, “Lectures on Chemistry.” Fordyce, “On Compound Elective Attractions,” fol. 2. Cullen, “Rough Notes Taken by David Carmichael”; Cullen, “Lectures on Chemistry.”

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that it had a stronger attraction to the vitriolic acid than to the nitrous. The former would therefore be the strongest menstruum for that solvend, and the latter the weakest. Studying the column for silver (or for metallic substances generally) would indicate that vitriolic acid was a stronger menstruum for this solvend than the nitrous. In both cases the vitriolic acid was the strongest menstruum, while the nitrous was the weakest. Similarly, the columns for vitriolic acid and nitrous acid would confirm that in both cases the strongest solvend was the fixed vegetable alkali, while the weakest was the silver. So, any mixture of these four substances would effectively be pitting the weakest possible attraction (between the weakest solvend and the weakest menstruum—in Fordyce’s newly invented annotation ‘2m ! 2s’) added to the strongest possible attraction (between the strongest solvend and the strongest menstruum—‘1m ! 1s’) against two medium attractions (between the strongest solvend and the weakest menstruum—‘1m ! 2s’—and the weakest solvend and the strongest menstruum—‘1s ! 2m’).33 It is likely that Fordyce’s thinking was inspired by a reading of Robert Dossie’s recently published Institutes of Experimental Chemistry, which stated: When any two bodies of a different genus are combined, and a third of the same genus with either of them is added under the circumstances proper for their commenstruation, such third will not for the most part commenstruate with them, so as to become an additional element to the compound; but if it be of a superior or higher degree of attraction than that in the compound which is of its own genus, it will commenstruate with the other of the different genus from itself, notwithstanding the state of combination in which this was before with that of its own.34

This implied that, with regard to the columns of an affinity table, all the substances below the header row must be of the same genus (and of a different genus to the header substance). Those substances that would all be attracted by a single substance were thus grouped together as one genus, the substance to which they were attracted belonging to another. The affinities of substances were, in Dossie’s theory, fixed in the specific context of their classification. His further division of substances into species allowed him to assert, for example that: “oil of vitriol … is of the highest order of attraction in the series of the acid genus.”35 Dossie’s affinity table thus implied a general taxonomical structure, including, for example, a list or series of the orders of affinity of acids “with respect to each other in relation to alkalies,”36 and another of “alkaline salts, earths and metals with respect to each other in relation to acids.”37 It is not difficult to see a link between Dossie’s ‘genera’ and Fordyce’s ‘menstrua’ and ‘solvends.’ 33 34

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Fordyce, “On Compound Elective Attractions,” fols. 1–4. “Commenstruation” was a word coined by Dossie to signify “this power in bodies, of combining with each other in consequence of their specific attractions.” Robert Dossie, Institutes of Experimental Chemistry (London: J. Nourse, 1759), 8. Dossie, Institutes of Experimental Chemistry, 27. Dossie, Institutes of Experimental Chemistry, 275. Dossie, Institutes of Experimental Chemistry.

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Fordyce’s lengthy algebraic contortions, combined with just nine actual experiments, eventually led him to claim, as a general rule, that “we have sufficient reason to conclude that 1m ! 2s + 2m ! 1s is stronger than 1m ! 1s + 2m ! 2s.”38 In other words, in cases where the two medium affinities opposed the weakest and strongest added together, the two medium would outweigh their opposition. From Cullen’s 1757 lecture notes, it does not appear that at this point he had sought to emphasise a generalised scheme of his double elective attractions. It is interesting to note that the abovementioned example of nitrous acid/vitriolic acid/ fixed vegetable alkali/silver, which provided Fordyce’s first exemplar, was exactly the same as the third one that Cullen had offered his students in 1757, and which, quite probably, Fordyce had himself learned in that session. However, there is a slight divergence between Fordyce and Cullen’s ideas here, perhaps consequent upon Fordyce’s misunderstanding of Cullen’s diagrams, but more likely resulting from Fordyce’s quite different intentions in his own paper. Cullen had specifically stated that his diagrams showed what happened when two already compounded substances were mixed. Double elective attraction was, as he also explained, the decompounding of these two compound substances and the production of two new compound substances from their constituents. Fordyce, on the other hand, sought to compare all the competing attractions within a mixture of four separate substances. As he noted: “In this demonstration we have supposed the bodies being mixt together disjoined.”39 This suggests an interesting distinction. Cullen’s point of view was practical—double elective attractions were intended to be used to separate substances that could not be easily divorced by the use of simple elective attractions. Indeed, the nitrous acid/vitriolic acid/fixed vegetable alkali/silver example used by both Cullen and Fordyce formed a puzzle that was well known to eighteenth-century chemists as an exemplar of the usefulness of affinity.40 Here, to appropriate Geoffroy’s 1718 phrase, affinity was to be used to “guide the operator.” Fordyce’s intention, in contrast, seems to have been to predict the results of mixtures of different substances, whether combined or uncombined; this was chemistry that was to be performed, where possible, in the head, or on paper rather than in the laboratory. Fordyce’s adaptation of Dossie’s ideas also sought to exploit the fact that in the majority of mixtures of four substances there were not, as might 38 39 40

Fordyce, “On Compound Elective Attractions,” fol. 8. Fordyce, “On Compound Elective Attractions,” fol. 7. E. F. Geoffroy had drawn attention in one of his papers on affinity to a question posed by Stahl to Neumann: how to separate vitriolic acid from fixed alkali (combined as vitriolated tartar) in the palm of the hand (that is, in a heat no more than that of the human body). See E. F. Geoffroy, “Eclaircissement sur la table insérée dans les mémoires de 1718 concernant les Rapports observés entre différentes Substances,” Histoire (et Memoires) de L’Academie Royale des Sciences 1720 (1722): 20–34, on 28. Leaving aside the doubtful wisdom of performing chemical operations using one’s hand as crucible, this demonstrates the utility of affinity theories in suggesting new, safer and perhaps cheaper ways to perform operations traditionally requiring heat. The affinity between vitriolic acid and fixed alkali was believed to be amongst the strongest known, so no separation could be envisaged by the addition of a third substance. The application of heat appeared to be the only option. Although Geoffroy offered a number of solutions to the riddle, the solution was also given, as Cullen explained to his students, in a letter from Stahl’s son to Boulduc. See J. R. Partington, History of Chemistry (London: St. Martin’s Press, 1961), vol. 2, 704.

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sometimes be imagined, six competing affinities acting, but just four.41 Acids, as menstrua, would not combine together, and nor, in most cases, would the various kinds of solvends. Fordyce’s attempted rule was, as we shall see, unconvincing to its audience. This is of less significance than the fact that he made it at all. His paper sought to improve on Cullen’s teaching on double elective attractions by incorporating his own ideas, themselves based upon a refashioning of Dossie’s work. The pupil sought, in this case, to teach the teacher. It is clear that Fordyce accepted the foundational status of affinity in chemistry, as well as the expectation, derived from Cullen’s teaching, that the best possible opportunity for the improvement of the discipline lay in a better understanding of affinity. At the same time, however, he apparently believed that Cullen’s teachings on double elective attractions (or compound affinities, as Fordyce called them—the choice of a new phrase perhaps suggesting Fordyce’s intention to strike out on his own) left something to be desired. Perhaps we also catch a glimpse here of the potential for misunderstanding and misconception in the gap between pedagogue and student.

Cullen’s response to Fordyce’s rule The Glasgow archives also contain two drafts of Cullen’s response. We unfortunately do not have a copy of the letter as it was eventually sent, but from Fordyce’s response, preserved in the same archive, we are probably safe in assuming that the tone was not hugely different from that of the drafts, which were extremely discouraging. The introduction to what seems to be the second draft gives a flavour of Cullen’s mood as he wrote it. Cullen’s sighs of frustration can almost be heard at appropriate points. He wrote: The Death of my Patient has set me at liberty and I have again sat down to consider your piece. After studying it with all the attention possible I must tell you that it is very difficult to be understood. Perhaps that is my fault but I think it not entirely for even these parts that I do understand are by no means expressed with the perspicuity they are capable of & I have consulted one or two of the best judges here & they also complain extreamly of your obscurity. I once intended to have been very particular in my criticisms but I now find that this would take more time than either you or I can spare at present.42

The letter was in fact originally even less positive, as is clear from the copious crossings out. Cullen described his own latest method of dealing with double elective attractions, offering a generalisation intended to remove some of the doubt from the prediction of complex reactions. The diagrams he now included in his letter to Fordyce were somewhat different from those contained in the lecture notes of 1757.43 The new diagrams (Figure 2) were described as: 41 42 43

Dossie, Institutes of Experimental Chemistry. Cullen, “Draft Letter to George Fordyce” (actually two drafts of the one letter). As noted by Crosland: Crosland, “The Use of Diagrams as Chemical ‘Equations,’” on 79–80.

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figure 2 Cullen’s diagrams as published in John M. D. Thomson, An Account of the Life, Lectures and Writings of William Cullen M.D (Edinburgh and London: William Blackwood and Sons, 1859), Vol. 1, 571. Image from author’s own copy.

rods, intersecting one another and movable on a common Axis in the point of intersection. At the extremities of each let there be placed substances that have an attraction for each of the substances on the extremities immediately contiguous to them & let the attractions be expressed by the letters w, x, y, z.44

Cullen then compared these attractions, using the affinity table for reference, to show that in two of his examples, “y > x & z > w by table, Ergo y + z > x + w.”45 As the affinity labelled ‘y’ was greater than that labelled ‘x,’ and that labelled ‘z’ was greater than that labelled ‘w,’ the total represented by affinity y and affinity z could be reasonably believed to be greater than the sum of affinities x and w. Here, Cullen compared the competing affinities in a mixture in a very similar way to that adopted by Fordyce in his paper. Although Cullen states that “he fell on [this system] last session,” this is the first record of his new methodology. This comment 44 45

Cullen, “Draft Letter to George Fordyce.” Cullen, “Draft Letter to George Fordyce.”

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was previously interpreted as implying that Cullen had actually presented these new diagrams as part of his latest chemistry course. However, it would be a notable coincidence for Cullen to have changed his methodology immediately prior to receiving Fordyce’s paper, and I would like to suggest a reinterpretation of the exchange, by re-examining what appears to be the first draft of the letter, which Cullen apparently began immediately upon receiving Fordyce’s letter46—before he had settled down to read the paper properly. In the first draft, Cullen writes: “In treating of double elective attractions last session, I managed it in this way.”47 He then sets out to describe diagrams in terms that suggest that he is using his standard ‘dart’ system for three cases out of the four treated by Fordyce (unfortunately, “the adjouned Diagrams” he refers to do not accompany the draft). When he comes to treat of the fourth, however, it is clear that he feels a different approach will be necessary: “This last case will perhaps be better illustrated in this manner. Suppose two Rods crossing one another but moveable …”48 It seems from this that the new diagrams used in Cullen’s second draft were not, in fact, used in his 1759 teaching session, but were actually devised specifically in order to respond to Fordyce’s paper, and indeed were prompted by Fordyce’s own ideas. Cullen perhaps believed that in order to explain his objections clearly to Fordyce he would need to translate his diagrams into Fordyce’s own language. The Royal College of Physicians in Edinburgh holds a set of notes from the early 1760s (unfortunately undated, and impossible to date more precisely) in which Cullen combined his ‘dart’ diagrams with a comparison of the various affinities along very similar lines to those contained in his response to Fordyce’s paper (see Figure 3).49 In this manuscript, additional notes are just visible around the affinity diagrams comparing the differing strengths of the affinities represented by the diagrams (in the figure, faint marks of “c > a” and “c > b” are discernable). The notes indicate that he introduced this kind of comparison as a way of articulating his theory of double elective attractions. This is not to suggest that Cullen appropriated Fordyce’s diagrams as such; indeed, he did not, adhering as he did even in this lecture to his usual dart diagrams. Rather, I would argue that, however, unsatisfactory Fordyce’s paper was in Cullen’s view, he found certain of Fordyce’s ideas as expressed in the exchange of correspondence somewhat persuasive. This was not the one-way bestowal of instruction by a master on his student; it appears that with Fordyce’s emancipation, he was approaching the status of a potential collaborator, a colleague and fellow philosophical chemist.

46

47 48 49

Although the first draft is undated, we know from another letter Cullen wrote on 4 October to Dr Balfour Russell (quoted below) that he had been puzzling over Fordyce’s paper for around eight days. William Cullen, “Letter Cullen to Dr Balfour Russell” (1759), MS 156, Cullen Papers, Glasgow University Library, Glasgow. Cullen, “Draft Letter to George Fordyce.” Cullen, “Draft Letter to George Fordyce.” William Cullen, “Lectures on Chemistry” (n.d. [1760s?]), EXH/CUL/2/2/1 (formerly MS Cullen 10), Library of the Royal College of Physicians, Edinburgh.

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figure 3 Detail showing diagrams of double elective attractions, from William Cullen, “Lecture Notes” (1760s), Library of the Royal College of Physicians of Edinburgh, EXH/ CUL/2/2/1 (formerly MS Cullen 10), fol. 72. By kind permission of the Royal College of Physicians of Edinburgh.

As the exchange progresses, it becomes clear that Fordyce felt this way, and Cullen acknowledged the point. Having said that, it is unclear whether Cullen found this a successful pedagogical approach, as later sets of notes do not appear to contain this kind of comparison.50 While Fordyce may have been approaching the status of a fully fledged philosophical chemist, it appears he had not quite attained that height yet. Cullen was unequivocal in advising Fordyce not to send his paper as it stood to the Royal Society. This part of the letter was later quoted in Thomson’s life and work of Cullen.51 He advised that Fordyce should “Shew it to some persons of patience judgement and Candour. Every body needs the corrections of their friends & every body should consult them before he appears in public.”52 So far as Fordyce’s theorising was concerned, Cullen clearly felt that Fordyce had failed to either explain or 50 51

52

Cullen, “Notes Taken by Charles Blagden.” John M. D. Thomson, An Account of the Life, Lectures and Writings of William Cullen M.D (Edinburgh and London: William Blackwood and Sons, 1832), Vol. I, 126. Cullen, “Draft Letter to George Fordyce.”

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justify his speculations sufficiently to allow them to be exposed to the critical world; and he seems to have been keen to prevent him from taking his ideas into the public arena without more clarity: If you still think your Essay worthy of the public I must beg of you to have the composition mended in every part. I would have you set out with the use & importance of the doctrine of Elective Attractions the State of it hitherto & a clear enunciation of what you further propose in your Essay. Let the expression in every part be more correct and take care that your propositions explanations & illustrations be more perspicuous. … At best it is an abstract consideration that few are willing to enter into & there are at the same time so very few chemists that at best you are to expect few readers & in the present state of your Essay none at all. I would also have you support the dryness of the subject by a number of facts & if possible new ones.53

Fordyce had also enclosed with his letter a neatly cut out affinity column showing the affinities of nitrous acid. This is preserved together with the paper held at Glasgow University Library. For this evidence of careful experimental zeal, Cullen expressed his gratitude. Although he clearly had many reservations about Fordyce’s theory, he had little doubts about his experimental ability, as is evident from the fact that he added the column to the tables he presented to his students, albeit in addition to, rather than replacing, the earlier column for that substance. Fordyce’s column for nitrous acid (very slightly modified) is found in a number of affinity tables appearing in sets of notes from Cullen’s lectures from the 1760s, and it appears that Cullen gave due credit for this column to Fordyce in his lectures.54 In the same year that included Fordyce’s idea of comparing the competing attractions in double elective attractions, Cullen also included Fordyce’s nitrous acid column: This is pretty universally agreed upon by all chemists, except Dr Fordyce; who had endeavoured to correct it by Experiments, for this reason I have added [the new column], repeated according to his determination, perhaps Dr Fordyce is mistaken with regard to platina, for all alchymists say that this substance has no regard to [nitrous acid]. But platina is often united with iron and this circumstance might mislead him.55

Fordyce persists The final word from 4 October 1759 is given in a letter written on the same date, apparently, by Cullen to another of his ex-students, Dr Balfour Russell: I have this day finished a letter to Fordyce that might, tho’ I shall not insist on it, excuse me for two years to come. He has puzled me these eight days with his compounded—I had almost said confounded—attractions & you should have saved me, by telling him 53 54

55

Cullen, “Draft Letter to George Fordyce.” Cullen, “Notes Taken from Lectures on Chemistry,” MS/MSL/79a-c; Cullen, “Notes Taken by Will Falconer from Chemistry Lectures.” In this latter manuscript, Cullen credits Fordyce for this column, and explains to his students the slight amendments he has made to Fordyce’s column. Cullen, “Lectures on Chemistry,” EXH/CUL/2/2/1 (formerly MS Cullen 10).

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honestly how difficult his piece was. If you did not find it so I admire your quickness. I am sorry I have been oblidged to check him a little for I expect much good of him at last & I excuse your complacency in saying it was all very clear, but you must shew him what I have said to you … 56

In spite of all this, though, it does not seem that either Cullen or Dr Russell dissuaded Fordyce from a robust defence of his ideas. Glasgow University also holds Fordyce’s response to Cullen’s letter, in which he argued, first apologising for what he was about to say, I think it is the way you consider the subject, which upon recollection youl find is the way almost every body has consider’d it, that has made it so difficult for the law you mention appearing so evident to every body … and if youl be so good as to reflect I believe you’l find your diagrams illustrations of my doctrine and not of that law.57

Clearly Fordyce was not too crushed by his old master’s criticisms. There is, however, some indication that Fordyce was concerned that an accusation might be levelled at him of borrowing rather too much from Cullen’s lectures. He concluded his letter, I ow[e] what ever I know of Chymistry and physick to you and if you think I have borrowed any hint from you I shall always be ready to own it or rather throw the copy you have into the fire and I shall serve the one I have in the same manner.58

He did not give up his paper easily though, as we can see by yet a third letter to Cullen, defending his point of view, particularly with the statement: I think it would be of use to introduce sometimes mathematical reasoning into chymistry where it will admit of it as by that means some curious propositions might be found out and it wuld give it more the air of a science.59

The notion of mathematising chemistry was not new, although it had fallen somewhat out of favour since the rather fruitless attempts of Newton’s disciples, most notably John Keill and John Freind, to explain chemical phenomena on the grounds of physical attributes of particles.60 Although Cullen taught his students to take an empiricist view, he took a balanced position, advocating neither the strict avoidance of theory, nor the speculative theorising of the philosopher. Mathematics was, for Cullen, primarily the tool of the natural philosopher rather than the chemist; indeed this was one of the factors distinguishing chemistry, as the study of particular qualities of particular bodies, from natural philosophy, which studied the general qualities of all matter. It is interesting to see Fordyce, now slightly removed from the sphere of Cullen’s 56 57 58 59 60

Cullen, “Letter Cullen to Dr Balfour Russell.” Fordyce, “Five Letters to William Cullen,” MS 180, Letter 2. Fordyce, “Five Letters to William Cullen,” MS 180, Letter 2 (undated, but probably 1759). Fordyce, “Five Letters to William Cullen,” MS 180, Letter 3 (undated, but probably 1759). For example, John Keill, An Introduction to Natural Philosophy: or Philosophical Lectures Read in the University of Oxford, 1700 (London: William and John Innys, 1720) and John Freind, Chymical Lectures: In which almost all the Operations of Chymistry are reduced to their True Principles and the Laws of Nature. Read in the Museum at Oxford, 1704 (London, Jonah Bower, 1712).

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influence, offering, in his slightly aggressive-defensive way, his own thoughts on this. The paper on compound elective attractions never did appear in the Philosophical Transactions, and there is no evidence that it was ever sent to the Royal Society. But Fordyce was about to travel to Leiden to further his medical education, and it is possible that events overtook him.

Affinity revisited By 1765, Fordyce had apparently revised his affinity theory, at least for pedagogical purposes. The basis of the theory, which he would continually adjust and amend throughout his career, is contained in a set of lectures from that year also held by Glasgow University Library.61 His Elements of Agriculture provides further valuable information on his affinity theory at that time.62 This work included both an explanation of his theory and its application to the problems of agriculture. The familiar terms ‘menstruum’ and ‘solvend’ that Fordyce had introduced into his theory of compound attractions were also used here, to distinguish the two elements that combined together chemically to form a compound. We find a further hint in the 1765 lectures that he had not in fact given up entirely on his ideas of six years earlier. Here he described to his students a new kind of diagram that they might sketch as a tool for accurately predicting the outcome of a compound affinity (Figure 4). This seems to have been derived from those he suggested in his early paper combined with Cullen’s ‘rod’ diagrams, with each substance’s strongest and weakest attractions labelled.63 He also presented a generalised rule that he claimed governed such mixtures, and again we see a hint here of his ideas of 1759: Hav[in]g thus placed these subst[ance]s in ye Diagram with their stronger & weaker attractions, we next examine where we find weaker, weaker placed on the same side of ye diagram, these we may conclude cannot unite together—thus we find here, weaker, weaker placed between ye mercury & ye nitrous acid, these we conclude cannot unite together; the nitrous acid therefore must unite with ye alkali, & ye vitriolic acid with the mercury. So we find it is in fact.64

Although some of his less sustainable claims from his earlier paper are absent, it appears that his desire to set his chemistry on a mathematical and predictive footing was undimmed. Fordyce’s affinity theory was carefully formulated to correspond to 61

62

63 64

George Fordyce, “Notes Taken by John Samwell from Chemistry Lectures” (1765), MS Gen. 786, Glasgow University Library, Glasgow. Further sets of lectures (although much later in date) are held by the Royal Society of Chemistry, King’s College London, and the Royal College of Physicians of London. George Fordyce, “Lectures on Chemistry” (n.d. [1770s?]), MS 172, Ferguson Papers, Glasgow University Library, Glasgow; George Fordyce, “Lectures on Chemistry 1786” (1786), MSS 146–148, St Thomas’s Hospital, Henry Rumsey Papers, Royal College of Physicians, London; George Fordyce, “Lectures on Chemistry 1786” (1786), MS E 146 G, Historical Collection, Royal Society of Chemistry Library, London; and George Fordyce, “Notes Taken by Richard Whitfield from Chemistry Lectures” (1788), M58-M60, St Thomas’s Collection, King’s College Library, London. Fordyce, Elements of Agriculture. This work is undated, but evidence in other sources confirms it as having been published for the first time in 1765. Fordyce, “Notes Taken by John Samwell,” MS Gen. 786, fol. 60. Fordyce, “Notes Taken by John Samwell,” MS Gen. 786, fol. 61.

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figure 4 Detail, George Fordyce, “Notes Taken by John Samwell from Chemistry Lectures” (1765), Glasgow University Library, MS Gen. 786, fol. 60. By kind permission of Glasgow University Library, Special Collections.

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the rest of his chemistry, and indeed it dictated much of it, whether in terms of the practical solutions advanced to chemical problems, or in the details of his complex matter theory.65 Affinity continued to occupy a crucial role in Fordyce’s chemical pedagogy, although his faith in affinity tables was somewhat reduced over the course of his lecturing career. The twenty-three pages of the 1765 lecture transcripts devoted to Fordyce’s affinity table can be compared to the single sheet included in the 1786 and 1788 lectures.66 Indeed, it seems that his speculations on the combinations of particles of chemical elements may well have contributed to his increasing apostasy. In 1786 he gave his students some idea as to why tables should be used with caution: A great number of substances which we consider simply chemical Elements are really & in fact Compounds. So that when we are performing a simple elective attraction as we suppose, it frequently is not a simple elective attraction but a compound one. This makes great derangement of great Difficulty in forming Tables of elective attraction; for the same substances do not combine together by compound elective attractions as we should expect from simple elective attractions.67

He continued, Chemical elements being many of them, perhaps all of them, Compounds, we are frequently forming compound elective attractions instead of simple ones, which is a Source of great Error in Tables of elective attractions that have hitherto been made, so that we can hardly trust to them, unless under particular Circumstances of Experiment.68

The problem was not, it would seem, with the principles of affinity theory, or even with the notion of an affinity table, but with the state of chemical knowledge at the time. The creeping doubts about the composition of a variety of substances, in particular the array of new airs that were filling the chemical atmosphere, caused Fordyce to present his later students with a more generalised affinity table, consisting only of seven columns showing the affinities of acids, alkalis and earths, metals, sulphur, water and fixable air. This provides a notable contrast to Cullen’s 1765 table of thirty-one columns. Fordyce’s loss of faith contrasted with the trend followed by most chemists. Bergman published his huge affinity table of fifty-nine columns (in both the wet and the dry way) in 1785, while in 1799 George Pearson, MD at St George’s Hospital, London, who had studied under Cullen and Black at Edinburgh as well as under Fordyce at St Thomas’s Hospital in 1774, published a translation of the Table of Chemical Nomenclature that included an oxygenated affinity table, derived from Bergman’s, of sixty-two columns.69 65 66

67 68 69

See “Part I,” on 51. Fordyce, “Lectures on Chemistry 1786,” MS E 146; Fordyce, “Notes Taken by Richard Whitfield from Chemistry Lectures,” M58–M60. Fordyce, “Lectures on Chemistry 1786,” MSS 146–148, Lecture 8. Fordyce, “Lectures on Chemistry 1786,” MSS 146–148, Lecture 8. Anon. [George Pearson], A Translation of the Table of Chemical Nomenclature Proposed by De Guyton, Formerly De Morveau, Lavoisier, Bertholet, and De Fourcroy with Explanations, Additions, and Alterations to Which Are

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Cullen and Fordyce reassessed Where Part I of this paper provided a broad comparison of the chemistry courses of Cullen and Fordyce, Part II has offered a more concentrated examination of their affinity theories. Though both men chose to set affinity at the heart of their chemistry teaching, this did not mean that they agreed completely on the details of their theories. A good illustration of this pattern of similarity and divergence can be seen in a simple example offered by both Cullen and Fordyce to show their students that in true chemical combination—or, in Cullen’s terms, proper mixture—the properties of the constituents (or, to Fordyce, elements) were lost, and new ones gained by the compound substance. In 1766, Cullen divided kinds of union into mechanical mixture, chemical solution and proper mixture, of which only the last was a true chemical combination. He explained to his class: A Solution of common salt in Water is not a proper mixture; because … , it still retains its peculiar properties nor is a solution of alkali in water, for the same reason; but if it be combined with acid, … a proper mixture ensues; & this may be distinguished from Chl solution, by the loss which each of the combined Bodies suffers of its peculiar Qualities.70

Fordyce also used the example of common salt dissolved in water, but he drew rather different conclusions. He divided types of union into mechanical mixture and chemical combination, although he does seem to have envisaged some type of continuum between the two extremes. In his scheme, a solution of salt in water counted as chemical combination—as noted above, he claimed that affinity could act between two solids that, in combination, produced a fluid substance. Salt and ice were, of course, two solids, from which salt-water, a fluid, resulted. Fordyce turned Cullen’s argument around, claiming that: if you make a solution of Salt in water, we are apt to say that the Salt gives the Taste to the water; but it does not. Salt is as insipid as water. If you apply dry Salt to the Tongue provided the Tongue likewise be perfectly dry so that no Part of the Salt shall be dissolved in water, it has no taste. The Taste which is acquired is the Taste of the Compound & not the Taste of either of the Elements.71 69

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Continued Subjoined Tables of Single Elective Attraction, Tablers of Chemical Symbols, Tables of the Precise Forces of Chemical Attractions and Schemes and Explanations of Cases of Single and Double Elective Attractions (London: J. Johnson, 1799), 106–106. Pearson studied medicine at Edinburgh under Cullen, although his chemistry was learned from Joseph Black. From 1774, according to contemporary sources, he studied under Fordyce at St Thomas’s Hospital, although we do not know whether he attended his chemistry lectures. This would seem to be a safe assumption, given that he quoted copiously from Fordyce’s “chymical lectures” in George Pearson, Observations and Experiments for Investigating the Chymical History of the Tepid Springs of Buxton; Together with an Account of Some Newly-Discovered, or Little Known Properties of Substances Relating to Several Branches of Chymistry, and Animal and Vegetable Life; to Which Are Prefixed a Chronological Relation of the Use of Buxton Water from the Earliest Records to the Present Times, Sketches of a History of the Atmosphere of the Peaks, and of the External Form and Internal Structure of the Mountainous Regions of Derbyshire; Intended for the Improvement of Natural Science and Art of Physic, 2 vols. (London: J. Johnson 1784). Cullen, “Notes Taken by Charles Blagden,” Lecture 25.

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For both Fordyce and Cullen the distinguishing factor in proper mixture or chemical combination lay in the loss of the properties of the constituents in combination. For both, this was the most important effect of the affinities between combined bodies. Although they agreed on the criteria, Fordyce saw solution as combination (as indeed his assimilation of Dossie’s menstrua and solvend classification into his science required), while Cullen did not. Cullen’s position, although at first sight anomalous, was in fact quite consistent with the affinity theory that loomed so large in his teaching. Fordyce’s position was, in turn, in conformity with his own theory. Their divergence lay in part in their comparison of the properties of salt before and after combination, and this contradiction illustrates the difficulties that must arise when taking such a subjective property as sapidity into account. However, they also interpreted their observations in subtly different ontological terms. Cullen seems to have inspired Fordyce with a seemingly boundless enthusiasm for chemistry and its many and various applications, which he sought to put to use when the opportunity presented itself. The ‘biographical sketch’ in the Gentleman’s Magazine that appeared on Fordyce’s death described him as “the author of many improvements in various arts connected with chemistry, on which he used frequently to be consulted by manufacturers.” He certainly seems to have become the preferred source of chemical knowledge for many in London. However, the high status he undoubtedly attained (despite some notable foibles, including a ‘carelessness’ about his dress, and occasional habit of lecturing in the same clothes that he had worn the previous day, having failed to go to bed72) was not simply in consequence of having imbibed Cullen’s knowledge for later regurgitation. Cullen was a teacher who encouraged his students to form their own ideas and opinions (even if he could be less than complimentary regarding their articulation of these ideas), and Fordyce did not need much encouragement. Indeed, the Gentleman’s Magazine comments that he was “inspired … with that confidence which frequently attends the conscious possession of great talents.”73 This view is rather borne out by the exchange of correspondence with Cullen. It was presumably this blithe self-confidence that led Fordyce to begin lecturing on his own account so soon after leaving Edinburgh University, formulating the matter theory described in Part 1 by the age of thirty. Having earlier argued that Fordyce’s pedagogy was moulded from his own experience of Cullen’s teaching, although with his own distinctive additions and modifications, I hope to have demonstrated in Part II that the dynamics of knowledge transfer between Fordyce and Cullen were by no means uncomplicated. Knowledge and ideas were transferred ‘upstream’ from student (or ex-student) back to master. 71 72

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Fordyce, “Lectures on Chemistry 1786,” MSS 146–148, Lecture 5. See “A Biographical Sketch of Dr. George Fordyce,” Gentleman’s Magazine, 72, Part 1 (1802): 588–590. The anonymous author also comments that “His manners … were less refined and his address in general less studied, than what most persons in this country regard as proper for a physician. From these causes, and from his spending no more time with his patients than what was sufficient for his forming a just opinion of their ailments, he had for many years but little private employment in his profession; and never, even in the latter part of his life, when his reputation was at its height, enjoyed nearly so much as many of his contemporaries.” “A Biographical Sketch,” 588.

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Chemical facts, in the form of Fordyce’s affinity series for nitrous acid, passed from Fordyce to Cullen, and we have reasonable grounds for suspecting that Fordyce’s modifications of Cullen’s affinity ‘equations’ were influential (albeit temporarily) on Cullen’s own pedagogy. We must of course be cautious when taking lessons from one case study of one particular teacher and his equally particular student, yet it might tentatively be suggested that, while pedagogical practices in Enlightenment Britain were often inherited and carried forward in a hierarchical model as we might expect, the model for the transfer of the content of such pedagogy—its ideas, theories, tacit and explicit knowledge—was far more akin to a social network. Thus, while we might view Fordyce as Cullen’s pedagogical progeny and tactical translator (as indeed Fordyce was presumably a pedagogical progenitor himself), for a more complete and subtle picture we must concede that he was also Cullen’s chemical collaborator … and vice versa.

Acknowledgements I would like to thank in the first instance the staff of the various libraries and archives that I used in my research, but most especially the staff of Glasgow University Library Special Collections Department and the archivist of the Royal College of Physicians in Edinburgh, who for more than a decade now have assisted me and acceded to my numerous requests with kindness and promptitude. Thanks also to the Editor of Ambix and the anonymous referees who all assisted in making this paper better than when it started out. And finally, my friends and colleagues outside of academia, Peter, Alastair, Alan, Adam, Hujir and Luke (collectively, Synthetix Ltd) who cheerfully put with my obsession and listen to me expounding on it with (apparent) interest.

Notes on contributor Georgette Taylor completed her PhD in 2006 at University College London, on the affinity theories that were prevalent in the chemistry of eighteenth-century Britain. Her research explored the teaching of chemistry, in particular by William Cullen and by many of his ex-students. She won the 2008 Partington Prize for “Tracing Influence in Small Steps: Richard Kirwan’s Quantified Affinity Theory.” A postdoctoral fellowship followed with the project “Analysis and Synthesis in Nineteenth-Century Chemistry: Towards a New Philosophical History of Scientific Practice.” At present, she is an honorary research associate at UCL, while also working as a research and development manager at a software company, pursuing a degree in mathematics, and continuing her research on eighteenth- and nineteenthcentury chemistry. Address: 5 Dobson Walk, Wimblington, March, PE15 0PN. Email: [email protected]

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