1 We employ here the form Gur, since it is the most common among later scholars; variants such as Ghur and Guhr are also frequent and are sometimes used by one and a same author; we keep them in quotations.

2 See, for example: Dennehy, Myriam and Ramond, Charles, La philosophie naturelle de Robert Boyle, Paris: J. Vrin, 2009, pp. 111–112Google Scholar; and William R. Newman, ‘Newton's theory of metallic generation in the previously neglected text “Humores minerals continuo decidunt”’, in Lawrence M. Principe (ed.), Chymists and Chymistry: Studies in the History of Alchemy and Early Modern Chemistry, Sagamore Beach, MA: Watson Publishing International, 2007, pp. 89–100, 91. See also Norris, John A., ‘The providence of mineral generation in the sermons of Johannes Mathesius (1504–1565)’, Geological Society, London, Special Publications (2009) 310, pp. 37–40Google Scholar. Regarding Boerhaave's earlier views on the metalliferous principle of matter and mercury, we have already published two articles. See Alfonso-Goldfarb, Ana M. and Ferraz, Márcia H.M., ‘A Discussão sobre o Princípio Metalífico da Matéria na Royal Society e a Recepção das Memórias de H. Boerhaave sobre o Mercúrio’, in III Encontro de Filosofia e História da Ciência no Cone Sul, 2008, Águas de Lindóia. Filosofia e História da Ciência no Cone Sul, Campinas (SP): AFHIC, 2004, pp. 29–35Google Scholar; Alfonso-Goldfarb and Ferraz, ‘“Experiências” e “Experimentos” Alquímicos e a Experimentação de Hermann Boerhaave’, in Ana Maria Alfonso-Goldfarb and Maria Helena Roxo Beltran (eds.), O Saber Fazer e seus Muitos Saberes: Experimentos, Experiências e Experimentações, São Paulo: Educ/Editora Livraria da Física, 2006, pp. 11–42.

3 Mathesius, Johann, Sarepta oder Bergpostill, sampt der Jochimssthalischen kurtzen Chroniken, Nuremberg: Gedrückt zu Nürnberg durch Johan[n] von BergGoogle Scholar, [S.l.] : [s.n.], 1562. See also Norris, op. cit. (2).

4 Majer, Jiří, ‘Ore mining and the town of St. Joachimsthal/Jáchymov at the time of Georgius Agrícola’, GeoJournal (1994) 32(2), pp. 91–99Google Scholar, 94; see also Webster, John, Metallographia: or, An history of metals: Wherein is declared the signs of ores and minerals both before and after digging, the causes and manner of their generations, … As also, the handling and shewing of their vegetability, and the discussion of the most difficult questions belonging to mystical chymistry, … Gathered forth of the most approved authors that have written in Greek, Latine, or High-Dutch; with some observation and discoveries of the author himself, London: Walter Kettilby, 1671, p. 17Google Scholar.

5 All biographical information on Mathesius is taken from Georg Loesche's biographical essay appended as a preface to his selection of Mathesius's writings, Bibliothek deutscher Schrifstelle aus Böhmen, vol. 4: Mathesius, Johannes, Ausgewählte Werke, Erster Band: Leichenreden, 2nd edn, Prague: J.O. Calve'sche (Josef Koch) k.u.k. Hof- & Univ. Buchhandlung, 1908Google Scholar; the biographical essay is on pp. ix–xxxi.

6 On the context of Mathesius's preaching activity see Susan C. Karant-Nunn, ‘From adventurers to drones: the Saxon silver miners as an early proletariat’, in Thomas Max Safley and Leonard N. Rosenband (eds.), The Workplace before the Factory: Artisans and Proletarians, 1500–1800, Ithaca, NY: Cornell University Press, 1993, pp. 73–99.

7 Mathesius, ‘Third sermon on the origin and decay of metals’, in idem, op. cit. (3), fols. 38–57, 52r.

8 Mathesius, op. cit. (3), fols. 39v, 39r.

9 Mathesius, op. cit. (3), fol. 49v.

10 See Calvör, Henning, Historische Nachricht von der Unter- und gesamten Ober-Harzischen Bergwerke, Hildesheim: G. Olms, 1990Google Scholar.

11 Webster, op. cit. (4); see, for example, Clericuzio, Antonio, ‘Alchimie, philosophie corpusculaire et minéralogie dans la Metallographia de John Webster’, Revue d'histoire des sciences (1996) 49, pp. 287–304CrossRefGoogle Scholar.

12 Webster, op. cit. (4), p. 51.

13 Paracelsus and Van Helmont are discussed below.

14 Stahl, Georg E., Traité du soufre (tr. P.H.T. Baron d'Holbach), Paris: Chez P.F. Didot, le jeune, 1766Google Scholar; the last part of the book is devoted to generation, quoting several authors; see pp. 209–213.

15 Stahl, op. cit. (14), pp. 212 ff., 255–7.

16 Stahl, op. cit. (14), p. 227.

17 Stahl, op. cit. (14), pp. 227–231; they probably expected to find particles of metal dissolved in the Guhrs which could be used to manufacture glass and coloured enamel.

18 Stahl, op. cit. (14), pp. 229–30, also p. 255; the similarities of Stahl's ideas and arguments to Van Helmont's is noticeable here.

19 Stahl, op. cit. (14), p. 230.

20 Stahl, op. cit. (14), pp. 230–231.

21 Stahl, op. cit. (14), p. 255.

22 The ‘primary Mixts’ are a ‘mixtion’ of at least two elementary principles, which makes them somehow palpable and manipulable since one elementary principle cannot exist in isolation; see Stahl, Philosophical Principles of Universal Chemistry (tr. P. Shaw), London: John Osborn and Thomas Longman, 1730, pp. 3 ff.

23 Stahl, op. cit. (14), pp. 231 and 256–257. As all his questions about the origin and location of this substance remained unanswered, Stahl concludes that the Guhr is rare and the vitriolic material is practically impossible to find.

24 Of French origin, Bassand was at the service of the Duke of Lorena and future German emperor Francis I; Lindeboom, Gerritt A. (ed.), Boerhaave's Correspondence, Part Two, Leyden: Brill, 1964, pp. 107Google Scholar ff. See also Knoeff, Rina, Hermann Boerhaave (1668–1738): Calvinist Chemist and Physician, Amsterdam: Koninklijke Nederlandse Akademie van Wetenschappen, 2002, p. 152Google Scholar.

25 Boerhaave to Bassand, 3 August 1732, in Lindeboom, op. cit. (24), pp. 302–305, 305.

26 Boerhaave to J.B. Bassand, 3 October 1732, in Lindeboom, op. cit. (24), pp. 304–311, 311.

27 Boerhaave to Bassand, 31 December 1732, in Lindeboom, op. cit. (24), pp. 310–315, 313.

28 The well-known Latin expression is aurum potabile.

29 Boerhaave to Bassand, 8 December 1733, in Lindeboom, op. cit. (24), p. 327.

30 The interest of Boerhaave in this magisterial formula is significant, and so will also be the conclusions he reaches. Although potable gold was an old medicine, opponents of Paracelsianism apparently tended to criticize and count it among the mineral formulae used in iatrochemistry. Thorndike, Lynn, History of Magic and Experimental Science, 8 vols., New York, Columbia University Press, 1923–1958Google Scholar, vol. 6, p. 250; on physicians employing this formula who did not adhere to iatrochemistry, see pp. 224 and 252.

31 On the use of potable gold among iatrochemists, and the criticism of it, see especially Debus, Allen, The Chemical Philosophy, 2 vols., New York: Science History Publications, 1977Google Scholar, vol. 1, pp. 122, 144, 154, 164, 185–186, 285; see also John Powers, ‘Scrutinizing the alchemists: Herman Boerhaave and the testing of chemistry’, in Principe, op. cit. (2), pp. 231 ff.

32 Boerhaave, Elements of Chemistry (tr. Timothy Dallowe), 2 vols., London: J. and J. Pemberton etc., 1735, vol. 2, ‘Process CLXI’, pp. 303–304.

33 This seems to contradict his opinion as expressed in one of his medical treatises, the Institutes of Medicine, written in 1708, at the beginning of his teaching career. See Dr Boerhaave's Academical Lectures on the Theory of Physics, 2nd edn, vol. 1, London: W. Innys, 1751, par. 1065.

34 Grasseus is not included in the discussion below, since he only reproduces Mathesius's text on Gur. See Arcana Arcani Artificiossisimi de Summis naturae mysteriis, in Johannem Jacobum Heilmannum (ed.), Theatri Chemici, vol. 6, Strasbourgh: Eberhardi Zetzneri, 1661, pp. 294–381; see pp. 305–6; 318. 14 John A. Norris has postulated a tradition he names as ‘gur theory’ for the ideas on the origin of metals; however, this seems an undue extrapolation. See his ‘Early theories of aqueous mineral genesis in the sixteenth century’, Ambix (2007) 54, pp. 69–86Google Scholar.

35 Agricola, Georgius, De ortu & causis subterraneorum de natura eorum quar efflunt ex terra; de natura fossilium; de veteribus & novis metallis; Bermannus, sive De re metallica Dialogus; Interpretatio Germanica vocum rei metallicae, addito Indice foecundissimo, Basel: Froben, 1546Google Scholar; we use here the translation De la generatione de le cose, che sotto la terra sono e de la cause de'loro effetti e nature lib. V; De la natura de quelle cose, che da la terra scorrono lib. IIII; De la natura de le cose Fossili, e che sotto la terra se cauano lib. X; De la minere antiche e moderne lib. II; Il Bermanno o de le cose metallice, dialogo / recato tutto hora dal latino in buona lingua volgare, Venice: Michele Tramezzino, 1550.

36 Agricola, De la generatione, op. cit. (35), fol. 67v.

37 Agricola, De la generatione, op. cit. (35), fols. 67v–69. Although Agricola does not mention Avicenna in this context, his starting point here is the latter's De congelatione (ed. Eric John Holmyard and Desmond C. Mandeville), Paris: P. Geuthner, 1927, pp. 39–40, which, however, he does not mention explicitly. According to the De congelatione only nature can form and perfect metals. Critics of alchemy often used this text; Agricola regards Avicenna's opinions as belonging to alchemical views and refutes them. The tradition of the De congelatione is confusing; its authorship sometimes even attributed to Aristotle.

38 Agricola, De la generatione, op. cit. (35), fols. 73–74v; Agricola initially directs his arguments against those who held metalliferous matter to be a sort of earthy matter or ash washed in water. The sequence of his argumentation shows, however, that this initial step was simply a pretext to deny that any fatty humour could originate metals; the argumentation is developed in fols. 70 ff.

39 Agricola, De la generatione, op. cit. (35), fols. 74v–75; according to Agricola, followers of this theory regard such greasy/fatty humour as a kind of sulphur or sulphurous material.

40 Agricola, De la generatione, op. cit. (35), fols. 182–182v, speaks of a frozen sap made of water and earth which would originate the mineral matter; in some cases this sap would mix with a fatty (but exogenous) material extracted by heat; cf. Agricola, De re metallica (tr. Herbert Clark Hoover and Lou Henry Hoover), repr. New York: Dover, 1950, pp. 34 and 47, where Agricola refers to De generatione.

41 Paracelsus, Aurora, & treasure of the philosophers, London: Giles Calvert, 1659, pp. 46–48.

42 Paracelsus, Paragranum, in idem, Medizinische, naturwissenschaftliche und philosophische Schriften (ed. K. Sudhoff and W. Matthiessen), 14 vols., Munich: Barth, 1922–33, vol. 8, p. 208.

43 Paracelsus, Paramirum, in idem, Medizinische, naturwissenschaftliche und philosophische Schriften, op. cit. (42), vol. 9, pp. 150–151.

44 Pagel, Walter, Paracelsus, Basel and New York: Karger, 1982, p. 359Google Scholar. Pagel's elegant construction is based on the De natura rerum, Das Buch de mineralibus and the Philosophia de generationibus, which he considers as the works par excellence where the views of Paracelsus on the origin of metals can be found.

45 Jan Baptist van Helmont, Magnum oportet [no. 39], in idem, Ortus medicinae, Amsterdam, Ludovicum Elzevirium, 1648, p. 157.

46 Jan Baptist van Helmont, Elementa [nos. 11–13], in idem, Ortus medicinae, op. cit. (45), p. 53.

47 Jan Baptist van Helmont, Aqua [nos. 5–7], in idem, Ortus medicinae, op. cit. (45), p. 58.

48 Sommerhoff, J.C., Lexicon Pharmaceutico-chymicum, Nuremberg, 1713, repr. Hildesheim: Olms, 1977, p. 45Google Scholar.

49 Webster, op. cit. (4), pp. 52–53.

50 See, for example, Leicester, Henry M., The Historical Background of Chemistry, repr. New York: Dover, 1971, pp. 123Google Scholar ff.; also the observation Partington makes that Boerhaave does not mention Stahl's theory of phlogiston by name (although he probably knew it), in Partington, James Riddick, A History of Chemistry, vol. 2, London: Macmillan, 1961, pp. 748–749Google Scholar. In contrast, Allen Debus has recently pointed out similarities between Boerhaave and Stahl despite differences in their views, in Chemistry and Medical Debate: Van Helmont to Boerhaave, Canton, MA: Science History Publications, 2001, pp. 217 ff.

51 Boerhaave, op. cit. (32), vol. 1, pp. 17–18, 17; the reference to the text of Stahl appears on p. 18.

52 The index of the Elements of Chemistry, op. cit. (32), reveals a few passages citing Stahl. His name does not appear in the index of the first volume of the English translation, which Boerhaave authorized and supervised, although, as mentioned above, one text of Stahl is cited there; the index of the second volume shows that the name of Stahl is mentioned (and is indeed found) only on pp. 287, 330 and 360.

53 Boerhaave, op. cit. (32), vol. 2, p. 287.

54 Boerhaave, op. cit. (32), vol. 2, pp. 330–331; on some of these processes see Alfonso-Goldfarb and Ferraz, ‘“Experiências” e “experimentos”’, op. cit. (2), pp. 11–42.

55 Boerhaave, op. cit. (32), vol. 2, p. 360.

56 Stahl, op. cit. (14), pp. 227–231.

57 See, for example, the letters from Boerhaave to Bassand dated 31 December 1732 and 20 July 1735, in Lindeboom, op. cit. (24), pp. 313 and 337.

58 31 December 1732, in Lindeboom, op. cit. (24), p. 313.

59 3 October 1732, in Lindeboom, op. cit. (24), p. 311; Boerhaave must have found this connection in the traditional tracts he cites. In fact, in criticizing the identification of the prime matter of the metals with a fatty substance, Agricola says that the alchemists who thought so considered such matter to be a sort of sulphur. See Agricola, De la generatione, op. cit. (35), fols. 71v, 74v–75.

60 Letter from Boerhaave to J.B. Bassand, 3 October 1732, in Lindeboom, op. cit. (24), p. 311.

61 Boerhaave, op. cit. (32), vol. 1, pp. 22–23.

62 Boerhaave, ‘Sur le mercure’, Histoire de l'Académie royale des sciences, année 1734 (1736), pp. 539–52, 539–540; idem, ‘Mercurio experimenta’, published in three parts, in Philosophical Transactions (1735) 38, pp. 145–67 (part 1), (1738) 39, pp. 343–359 (part 2) and (1738) 39, pp. 368–376 (part 3); see part 3.

63 Gibbs, F.W., ‘Cromwell Mortimer, F.R.S.: Secretary, Royal Society, 1730–1752’, Notes and Records of the Royal Society of London (1950) 7, pp. 259–263Google Scholar. On Boerhaave's memoirs on mercury see Debus, op. cit. (50), pp. 202–207; Powers, op. cit. (31). See also Alfonso-Goldfarb and Ferraz, ‘A Discussão sobre o Princípio Metalífico da Matéria’, op. cit. (2) where we highlight Boerhaave's idea of mercury as principle of metals.

64 Boerhaave sent his first memoirs on mercury in 1734, with a letter to Mortimer, to be read at the Royal Society; the second part of the work was initially read at the Académie royale des sciences; an English version by Mortimer was subsequently presented to the Royal Society, which also received the third part. The Mortimer–Boerhaave correspondence in 1733 and 1737 was published by Lindeboom, op. cit. (24), pp. 209–219. The memoirs containing the ‘Experiments on mercury’ were published in Latin, English, French, German and Dutch; cf. Lindeboom, Bibliographia Boerhaaviana, Leiden: Brill, 1959, pp. 86–87; we used here the Latin edition, ‘Mercurio experimenta’, op. cit. (62), along with the English translation of the first part in Some Experiments on Mercury, London: J. Roberts, 1734, and the French translation of the second part in ‘Sur le mercure’, op. cit. (62).

65 See the letter from Mortimer to Boerhaave dated 26 April 1737, Lindeboon, op. cit. (24), Part One, pp. 215–219, especially 219, and Boerhaave's response in 10 May 1737, pp. 219–220, 219.

66 Stahl, op. cit. (14), pp. 246–252, 246–247.

67 Stahl's Zufällige Gedancken und Nützliche Bedencken über den Streit von dem so genannten Sulphure, und zwar sowol dem gemeinen, verbrennlichen, oder flüchtigen als unverbrennlichen oder fixen, translated into French as Traité du soufre, was published in Halle in 1718, while Boerhaave's letter to Mortimer accompanying his first memoir to be read in the Royal Society dates from 18 February 1734; see Lindeboom, op. cit. (24), p. 209.

68 Burton, William, An Account of the Life and Writings of Herman Boerhaave, London: Henry Lintot, 1743, pp. 157–159Google Scholar.

69 Sage, Balthazar Georges, Eléments de minéralogie docimastique, Paris: P. De Lormel, 1772, p. 41Google Scholar.

70 Jakob Ludwig Karl Grimm and Wilhelm Karl Grimm, Deutsches Wörterbuch, Vierten Band, 1. Abteilung, 6. Teil, Leipzig: Verlag Von S. Hirzel, 1935, col. 1053.

71 On the identity of Gur and buttermilk-earth see Schmieder, Carl, Versuch einer Lithurgik oder ökonomische Mineralogie, 2 vols., Leipzig: Siegfried Lebrecht Crusius, 1804Google Scholar, vol. 2, p. 441.

72 Klaproth, Martin, Analytical Essays towards Promoting the Chemical Knowledge of Mineral Substances, 2 vols., London: T. Cadell, Jun. and W. Davies, 1801–1804Google Scholar, vol. 2, p. 113.

73 Klaproth, op. cit. (72), vol. 2, p. 121.

74 Klaproth, op. cit. (72), vol. 1, p. 249.