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Gur, Ghur, Guhr or Bur? The quest for a metalliferous prime matter in early modern times

Published online by Cambridge University Press:  20 October 2011

ANA MARIA ALFONSO-GOLDFARB and
MARCIA H.M. FERRAZ
ANA MARIA ALFONSO-GOLDFARB
Affiliation:
History of Science, Pontifícia Universidade Católica, São Paulo. Rua Caio Prado, 102, sala 48. 01333–000 São Paulo – SP, Brazil. Email: cesima@pucsp.br.
MARCIA H.M. FERRAZ
Affiliation:
History of Science, Pontifícia Universidade Católica, São Paulo. Rua Caio Prado, 102, sala 48. 01333–000 São Paulo – SP, Brazil. Email: cesima@pucsp.br.
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Abstract

It has been traditionally held that the idea of a prime matter of metals was abandoned in the eighteenth century, especially after the failure of Hermann Boerhaave to find it in mercury. However, documents tell a different story: the search for the metalliferous principle, in the form of an odd substance known as Gur, Guhr, Ghur or Bur, was very much alive in the 1700s. This was a project that involved Boerhaave himself, as is shown by his correspondence with J.B. Bassand. The first mention of this strange material appears in Sarepta, a collection of sermons by the sixteenth-century Bohemian preacher Johannes Mathesius, sometimes mentioned in the specialized literature but rarely studied. This paper discusses the various conceptions of this material held as the prime matter of metals, from Mathesius to the eighteenth century, involving reputed authors such as John Webster, Jan B. van Helmont, Georg E. Stahl and Boerhaave.

Information

Type
Research Article
Information
The British Journal for the History of Science , Volume 46 , Issue 1 , March 2013, pp. 23 - 37
Copyright
Copyright © British Society for the History of Science 2011

Introduction

Metallogenesis is usually believed to be relevant only to the history of geology or chemistry. However, a closer look into this subject shows that at least from the times of Aristotle, and up to the eighteenth century, the generation of metals was at the very centre of an all-pervasive discussion about the boundaries and possible connections among the three kingdoms of nature. In this regard, one particular focus of concern was whether species and ruling principles were exclusive to each kingdom or circulated among all three of them.

For this reason, questions concerning the origin and generation of metals had a direct implication for ideas on the very nature of matter, thus informing the theory and practice of the traditional fields of knowledge from medicine and pharmacy to philosophy and natural history, as well as new fields beginning to emerge in the early modern period. In this way, it can be seen that what initially seemed to concern mainly studies on matter was in fact a core notion to a broader scope of fields, giving us a peculiar glimpse into the paths of early modern science.

For, as research shows, the long-standing debate on metallogenesis resulted in the production of a large amount of extremely complex literature, partly due to the interest this subject had for a broad scope of disciplines, and partly because it described several notions, materials and processes that seem strange to the modern scholar. One of those strange materials was known as Gur. In time, the term Gur disappeared from modern dictionaries to be replaced by Kieselgur (or Kieselguhr), a common term in modern-day German for diatomaceous earth, a natural rock composed of fossilized remains of diatoms, a type of hard-shelled alga. However, until the eighteenth century, Gur was an everyday term employed by miners, preachers and scholars of minerals to refer to a substance that could be the much-coveted principle of metals.Footnote 1 As such, it could not fail to attract the attention of scholars such as Georg E. Stahl and Hermann Boerhaave. Although still in the nineteenth century Martin Klaproth included Gur among materials worthy of analysis, it has rarely been a focus of interest for modern scholars.Footnote 2 In this article, we focus on the connections within and among these different groups, whose particular interests did not necessarily converge.

It seems that the first written occurrence of the term Gur appears in the compilation of sermons of the sixteenth-century Bohemian minister Johannes Mathesius known as Sarepta, oder Bergpostill, sampt der Jochimssthalischen kurtzen Chroniken.Footnote 3 Mathesius had a special place in the collective mind of Bohemians mainly because of his concerns with education. His works had significant echoes, eventually reaching the capital and the court – surely no small feat for the son of a mine foreman from Joachimstahl in the Ore Mountains (today Jachymov, Czech Republic) whose parents died when he was seventeen.Footnote 4 He first studied at the university in Ingoldstat and later he travelled to Nuremberg, Augsburg, Munich and Wittemberg, employing himself as a private tutor. At some point in his journey he became a Lutheran, although it was through his connections with the circle of Bohemians in Saxony that he obtained the position at Joachimsthal, a centre of intense activity caused by a ‘rush of silver’, also touched by the currents of humanism and the Reformation pervading the country at large.Footnote 5 It is important to remember that this was a time when large efforts were devoted to the spread of Lutheranism, and one of the major tools was sermons. A charismatic character, Mathesius dressed up as a miner during the major holidays and preached to large popular audiences between 1553 and 1562. Sixteen sermons were compiled and published in 1562 under the title of Sarepta, a Greek version of the name of Zarephath, a mining village mentioned in the Bible; indeed, Mathesius called Joachimstahl ‘our Sarepta’.Footnote 6

Mathesius used common mining notions to explain Lutheran doctrines; for instance, he compared the Resurrection with processes and materials known to his audience, and in this way Sarepta came to represent the common ideas of contemporary miners regarding the origin of metals. In this context, Mathesius pointed to the signs that miners used ‘not to work in vain’ when searching for ores. They sought after Gur, a buttermilk-looking substance that flowed from the depth to the surface of the earth.Footnote 7 His guiding idea, in an analogy between biblical terms and mining processes, was that, like a child in the maternal womb, metals were placed in the interior of the earth by the Creator in an ‘incomplete’ form. Under the action of natural heat and water,

subtle or distilled earth and fatty heavy or smoky [earths] are made into seeds, and water and earth are tempered and mixed together, so that a ghur and sulphurous and mercurial seed is made, from which all ores and metals arise [literally ‘are sealed, fixated’], and admitting cold, they grow day after day, to become better metals, becoming dense and solid.Footnote 8

At the end of this process,

when a ghur or sulphurous and mercurial matter concurs or flows, it gets deposited in the fractures of the veins, or settles down there, as one can see in vitreous earths, where the still fluid drops gather together and in this way become manifest.Footnote 9

In other words, according to Mathesius, water and earths of several kinds form a first ‘seed’ that, under the action of heat and then water, becomes a second order of ‘seed’, namely Ghur, a sulphur-mercurial matter from which all metals arise. Initially fluid, it is able to circulate through the veins of the earth, and when it emerges to the surface, with a buttery appearance, it signals the presence of metals in a mine. Therefore it is possible to infer that Mathesius considered Ghur a metalliferous prime matter.

A ‘buttermilk-like substance’ instead of Gur was mentioned by another miners’ preacher, Johann Funcken, who lived in St Andreasberg from 1567 to 1629.Footnote 10 Nevertheless, Mathesius was not only the first to use the name Gur, but he also became the major reference point on this subject. So, for instance, he is mentioned by John Webster in Metallographia, or An history of metals (1671), one of the most important and widely read works on the subject.Footnote 11 It is curious that the first early modern review on Gur appeared in England rather than in the German area. Webster speaks of his interest in Gur, and how he had asked several people with good knowledge of the mines whether it actually existed. He eventually found help in an ingenious young man whose father had worked for him on many occasions and was an expert on the work in the lead mines of Derbyshire. Following Webster's instructions, the young miner managed to take to him some wooden plates containing a large quantity of Gur, which Webster describes as being ‘of a grayish colour or whitish colour, and would spread with one's finger upon a table, or smooth piece of wood, as like Butter as could be, but not so fatty, or greasie’.Footnote 12

The persistent interest of Webster in finding Gur was certainly based on sources on metallogenesis worthy of the utmost respect at that time, such as Johannes Grassaeus, Paracelsus, and Jan B. van Helmont, among others.Footnote 13

Text and subtext: an indirect dialog on Gur in the eighteenth century

An indirect and peculiar dialog on Gur took place later on, in the eighteenth century, between two of the most major figures in the history of medicine and chemistry: Georg E. Stahl and Hermann Boerhaave. It seems that the eighteenth-century work that mentions Gur most clearly within the context of metallogenesis is Stahl's Treatise of Sulphur, about one-third of which is concerned with metallogenesis.Footnote 14 According to Stahl, metals had been created mostly at once in veins within the womb of the earth. On the other hand, small amounts of new metals were daily produced not from one single principle but from the combination of principles resulting from the decomposition of other metals.Footnote 15 Among such principles there were ‘substances with all sorts of colours and consistencies, attached to each other here and there, which, coming out of the rocks, penetrate fractures and cavities; Miners call them by the name of stalactites, incrustations, concretes, Glimmer and Guhrs’.Footnote 16

Stahl observes that the Guhrs should receive more attention. Very colourful, pure and unctuous, they can be found in dry ground near veins of metals, though not in abundance. They do not have a proper name, being sometimes called Guhr, sometimes soot or rust. Nor do they have any specific use. However, they need to be better studied, since miners constantly look for these substances because they indicate the presence of rich mineral veins. Also, glass and enamel makers pay a good price for them depending on how pure and greasy they are.Footnote 17

Stahl notes that the Guhrs do not share the same origin as the common minerals or the minerals formed in immemorial times:

it is more natural to conjecture that they have been produced by the dissolution of metal combinations, and when they penetrated even further [in the ground], they must have been reduced to vapours and carried in this state to other, appropriate places, where they form a new combination when they find there are not only a matrix (matricem) but also a feeder (nutricem). Thus they form a new metallic mixture (mixtion) which can be called a true generation of a metal.Footnote 18

This promising matter, however, is not found in large amounts, nor does it appear in regular veins, conditions which are necessary to form metals in large quantities. The Guhrs constitute instead mainly ‘good signs and positive indicators which announce the proximity of a true good-quality vein’.Footnote 19 That is why people with experience in the work of mines regard them as excrescences or by-products of materials detached from the metal veins. Stahl therefore suggests, ‘The profound chemists who make such efforts to extract the principles of metals already formed will be able to see whether it would not be easier to find them in this sort of excrescences which sometimes follow the veins’.Footnote 20

While saying that these principles could be transformed into metals in the right place, Stahl, as is well known, never mentioned the existence of any prime matter in general. He rather believed that the metal veins originated in the ‘Creation’,Footnote 21 in which case the Guhrs would be in the category he defined as ‘primary Mixts’.Footnote 22 They were not, however, the only substances he considered as possible principles which would generate metals. There is also a ‘vitriolic substance [believed to be] the mother of all metals’. He pointed out that this substance, like the Guhrs, was difficult to find and resulted from the decomposition of metals.Footnote 23

Unlike Stahl, Boerhaave did not mention Gur in any of his published works, but we find a detailed discussion of Gur in his correspondence with Johann Baptist Bassand, a former disciple and physician at the imperial court in Vienna.Footnote 24

In a letter dated 3 August 1732, Boerhaave asked Bassand if in his many journeys he had met anyone who knew about Gur, a certain fluid matter, ‘like fat or candlegrease’, which is ‘formed into a mature and perfect metal by the coction of nature and subterranean heat’. Boerhaave further adds that he has never seen such material but thinks that it could cast light on the transmutation of metals and perhaps reveal medicinal properties which had been painfully sought in drinkable metals.Footnote 25

Boerhaave was not seemingly satisfied with Bassand's answer, as in the following letter he insists on the subject, saying that he had consulted most authors who wrote about the history of metals and they had unanimously agreed that

the first thing that is found in the matrix is an oily fluid, as dense as fat, but usually yellowish-green in colour, and this is what the German miners call Guhr in their own language; and that from this, after coagulation brought by coction of nature, all sorts of metals are formed, as it were, from the original matter to which they are most closely related.Footnote 26

Gur was a topic of discussion at least twice more in the correspondence between Bassand and Boerhaave. In a letter from December 1732, for example, the Leiden professor wrote that, according to several authors, Gur could be found in harder rocks, being ‘liquid soap, [a metallic humour] and yellowish-green in colour, which, when it hardens, produces a real metal, thus, it is said to be the primary matter in metal, soluble in water’.Footnote 27

Boerhaave kept reminding Bassand about the medicinal properties of this possible prime matter of metals, and took a step further in a letter dated December 1733, where he speculated ‘whether such primitive matter from which gold is formed could not be the true drinkable gold,Footnote 28 which is so adorned by very much praised virtues’.Footnote 29 This reinforced the importance of finding Gur, as one could then easily confirm whether it corresponded to the potable gold of alchemists, by carefully administering it to patients. According to him, the ‘processes’ using potable gold could be then better understood, a field in which scholars ‘set everything in motion, but advanced nothing’.Footnote 30 This kind of criticism of his contemporaries is common in his work. Contrary to appearances, however, it did not aim simply at his opponents’ way of thinking but also at their obscure explanations and at promises never fulfilled.

The passage above seems to reveal that Boerhaave believed in the existence of great Arcana concealed in the potable gold.Footnote 31 Drinkable gold, or Aurum Potabile, is mentioned only once in Boerhaave's Elements of Chemistry, in connection with what promises to be ‘The Preparation of Sulphur with an Acid and Alcohol’, to conclude by asking whether

it is with this that Paracelsus.’ Tincture of Gold is drawn, as to make an Aurum Potabile, digested, as he says, in the Stomach of an Ostrich? This Operation certainly should excite the curious to examine, but with prudence, whether any of these great Arcana lies concealed here.Footnote 32

To prove the equivalence between these and Gur could therefore unveil such Arcana, which were directly related to the principles of matter.Footnote 33

Just as Webster had done before, Boerhaave also mentions Mathesius, Paracelsus and Van Helmont as sources. But unlike the Englishman, the Leiden professor did not mention Johann Grasshoff (Grassaeus), but included Georgius Agricola. Thus, before going on with Boerhaave's elaboration, in order to understand the use he made of his sources, it is worth looking more closely at what these authors interested in the history of metals said about Gur and the metalliferous principle.Footnote 34

Agricola

Agricola devoted a whole book in his De ortu & causis subterraneorum to the generation, cause and nature of minerals.Footnote 35 Following very closely and elaborating on Aristotelian arguments, he referred to a certain sucus as the metalliferous prime matter. A significant part of his discussion was intended to refute alchemical conceptions concerning not only the transmutation but mainly the generation of metals in the interior of the earth.

To begin with, Agricola argued against the traditional theory of mercury and sulphur. He wrote that for centuries this theory, ‘with its astute and foul reasonings’, gained ground and infected even those working in mines.Footnote 36 Calling on his expertise on mines, he maintained that a vein of pure mercury and sulphur is very rarely found near veins of metals.Footnote 37 More concerned, in fact, with the status of alchemy and the practices of alchemists, he affirmed that alchemical process can only produce mere imitations of natural bodies. Despite the many claims by alchemists on the wonderful results of manipulating sulphur and mercury, it was not to be assumed that nature proceeds in the same way.

In the context of this attack on alchemy, Agricola mentioned a fatty matter with the same characteristics as Gur. However, Agricola denied that metals could be generated from a fatty matter at all. According to him, the fatty humour innate in animals and plants was the cause of their easy combustion. Since in metals combustion is always difficult, this kind of matter cannot be congenital and intrinsic, but extrinsic and adhering to them only by chance because of some accidental circumstance. Moreover, the fusion of metals never produced anything near a fatty, melted material. Agricola concluded that there was no need to postulate a fatty humour at the origin of metals; indeed no one would be able to explain the existence of such humour, unless perhaps it came from ‘the scabies of the infected Alchemists’.Footnote 38 In any case, Agricola regarded this conception as a variant of the theory of sulphur and mercury which he had already dismissed.Footnote 39 And indeed other passages dealing with metals in his work do not contain anything much different from what has been shown so far.Footnote 40

Paracelsus

Although one can hardly come to any definitive conclusion when dealing with Paracelsus, it is a fact that in his writings there is no mention of Gur or any similar material whatsoever, which, naturally, raises questions about why he would be mentioned as a source on this material by both Webster and Boerhaave. Paracelsus referred to vegetable materials which, fed with sulphur, would turn into perfect minerals, and he also referred to the mercury and sulphur of the ‘philosophers’ as taking part in the formation of metals.Footnote 41 However, all these references seem to concern the formation of minerals and metals in the depths of the earth rather than their materia prima.

Paracelsus probably followed in this case the traditional view that regarded elementary water as the matrix of mineral bodies. A passage from his Paragranum, for example, suggested that a sort of mucilaginous substance originating from water, through processes of separation and coagulation, would engender mineral bodies.Footnote 42 A similar reference exists in his Paramirum: ‘Behold the element of water in its undifferentiated state! And then see how all the metals, all the stones … gold and silver are derived from it; who could have recognized all these things in water’.Footnote 43

To reach a better understanding of this subtle scheme, it is worth consulting the work of Walter Pagel, one of the most distinguished scholars on Paracelsus. According to him, Paracelsus considered metals as an offspring of the element water developing inside the earth by means of the terrestrial archeus. In this scheme, the water enters the ground forming the shape of a tree whose fruits are the metals. Metals generated through this process do not come from any ‘sulphur or mercury or … the philosopher's stone of the alchemist. The latter can transmute, but – unlike nature – not generate de novo’.Footnote 44

Van Helmont

On the other hand, Van Helmont in several of his treatises mentioned a material which miners called Bur and existed in the veins of the earth. Similar to the Gur of Mathesius in all respects, this material had the consistency of liquid soap, its colours varying from very pale to dark green to yellowish and milky white. Found in the fractures and cavities of rocks in dry places, Bur could be easily seen on the top of elevations without any need to break the rocks. This sort of fluid also existed in underground canals, being ‘the first seed of metal life’ unknown to man because engendered in the depths of the earth.Footnote 45

Bur, Van Helmont argued, was a sort of mineral sap equivalent to the leffas in vegetables. Both came from quellem (a kind of earth or sand) originating from primeval water.Footnote 46 Particularly important was the fact that Bur was formed in the interior of the earth through the filtration of salty water, which lost its salt by the action of the archeus terrae and assimilated the seeds (semina) of various salts, minerals and native metals, thus generating vitriols, saltpetre, alum, sal-gem, marine-salt and other ‘primogenits of water’. According to Van Helmont, Bur engendered metals in places which are dry or where the water cannot penetrate the rock.Footnote 47 Therefore it represented the middle stage (middle-life) between the primogenial element and the metals. In a certain sense, it was a sort of an original metal, if not prime matter of metals.

Regarding Bur, an important eighteenth-century pharmaceutical–chemical lexicon by J.C. Sommerhoff attributed the term to Van Helmont and describes the substance as a mineral juice.Footnote 48 Webster observed that Van Helmont had referred to a material of ‘whitish greenness, which by and by hath thickened, like soft Soap’, and added, ‘This I would have the Reader to consider seriously of, in comparing it with the former relation; and to note, that, whereas he calls it Bur, I suspect the Print is false, and that it ought to be read Gur’.Footnote 49

Boerhaave versus Stahl?

In the light of what has been discussed above, it is curious that Boerhaave did not mention Stahl among his sources. This omission might not surprise many modern scholars who see these authors as opponents.Footnote 50 However, while Boerhaave's works do contain some elegant criticism of Stahl they also make some interesting and more sympathetic comments about him. For instance, Boerhaave's textbook Elements of Chemistry counted Stahl among those authors whose works have ‘digested the operations of Chymistry themselves into a regular system’ and therefore should be studied attentively. Nevertheless, it must be said, the Elements mentioned only one of the many books of Stahl, namely the Fundamenta Chymiae, which Boerhaave deemed very useful for understanding the application of chemistry in medicine and natural philosophy.Footnote 51

At any rate, Boerhaave rarely cited Stahl, and each and every citation of him is about cases somehow ‘extraordinary’.Footnote 52 One passage describes Stahl along with Johann Rudolf Glauber, Johann Joachim Becher, Robert Boyle and Wilhelm Homberg as ‘gentlemen of uncommon penetration in the more abstruse Mysteries of the Chemical Art’ who would be able to speak more about the effect of ‘Glauber's Sal Mirabilis’.Footnote 53 All these ‘Gentlemen’, except Glauber, also appeared in another place in Boerhaave's text as the ‘top Masters in Chemistry’, experts on a process involving the Luna Cornea and Aqua Regia which could under special conditions produce gold.Footnote 54 It is also worth mentioning a third case where Boerhaave discusses ‘The Alchemical Regulus of Antimony’ and concludes,

This Regulus has almost turn'd the Heads of some of the profoundest Chemists. Consult Paracelsus, Suchtenius, Philaletha, Pantaleon, Becher, and Stahl. And for my own part, when I reflect upon the Time and Pains I have employed in the examining into the nature of this Regulus, I can't help being surprised at my own Patience, and can hardly help blushing, to think, that so great a part of my Life should have been spent in this Inquiry.Footnote 55

Although not always approving, Boerhaave's comments on Stahl convey a certain respect for the persistent and elaborate work of a person who was his double as both: a physician and a chemist. However, his attitude was different with regard to the Treatise on Sulphur, which tackled several of the questions he would later ask Bassand.Footnote 56

Thus one can note that, several years later, Boerhaave raised the same problems as Stahl, regarding the same materials. Besides insistently asking Bassand for samples of Gur with no apparent success, in other letters he also requested a vitriolic material.Footnote 57 This material, chalcanth fossil, produced the natural green vitriol, which proved to be much more effective than the medicament artificially prepared at that time with the oil of vitriol.Footnote 58 This later request followed a letter to Bassand mentioning Gur, where Boerhaave said that ‘the prime matter of metals must be considered to bear more resemblance to vitriol than to quicksilver’. Boerhaave pushed the matter further than Stahl here by clearly relating Gur to a vitriolic matter.Footnote 59 He went on to affirm, ‘If this should prove to be consistently true, the dogma that metals are naturally formed from fire and quicksilver, or sulphur and mercury, as most Fathers of Chemistry, Homberg in particular, maintain, would appear to be false’.Footnote 60

How did this come to be so? Believing that the most important characteristic of metals was ‘gravity’ or weight (density), an initial phase of experimental work led Boerhaave to conclude that gold and mercury were almost similar. Further experience allowed him to hypothesize that the prime matter of metals was the purest kind of mercury obtainable through chemical operations. Indeed, he argued, as mercury gets closer to the weight of gold, the more refined it is, then it must be the simplest of bodies. Furthermore, an awareness of the easy manner in which mercury ‘unites’ with other metals, especially gold, led Boerhaave to suppose that ‘Mercury is the Basis of them all’, and to conclude that the main source of this basic mercurial matter – the purest mercury – was most probably mercury itself.Footnote 61

For more than fifteen years, Boerhaave carried out countless experiments to prove these hypotheses, whose results were negative: mercury was immutable and did not transform into other metals.Footnote 62 Boerhaave was persistent in this inquiry. He presented this series of experiments as three memoirs between 1734 and 1737 to be read at the Royal Society by its current secretary, Cromwell Mortimer, who was a former disciple of Boerhaave's.Footnote 63 One of them was also read at the French Académie royale des sciences, and the full set was published in the Philosophical Transactions of the Royal Society.Footnote 64 This represents further evidence of the widespread interest in a possible principle of metals until almost the middle of the eighteenth century. Mortimer wrote to Boerhaave that in spite of the negative results, he ought to continue with the experiments on the ‘purification’ of mercury, suggesting that perhaps increasing the heat would allow for the desired results, but this suggestion was rejected: Boerhaave warned his former student that no increase in heat could transform one metal into another.Footnote 65

The letter to Bassand mentioned above, then, shows that after much striving to seek the principle of metals in mercury, Boerhaave came to the very same hypothesis as did Stahl. The latter advocated in his Treatise on Sulphur the attentive study of Gur and considered it ‘impossible to demonstrate that the saline vitriolic matter is the main ingredient which produces the combination and generation of the metals’. He also ruled out the possibility that mercury triggered this process: for him, no idea could possibly be more strange and fanciful than considering mercury the origin of metals.Footnote 66 But Boerhaave had to work for fifteen years on the digestion and distillation of mercury before he was ready to raise new, divergent hypotheses.

Perhaps it was not by chance that the beginning of his works on mercury coincided with the time when Stahl published his Treatise on Sulphur.Footnote 67 In fact, it looks as if Boerhaave wanted to respond to Stahl by writing what could be called a ‘Treatise on Mercury’. Indeed, William Burton, another of his former students in Leiden, when writing an éloge of the master, regretted that death had prevented Boerhaave's attaining a couple of aims:

The one was to give a chronological history of the alchemists illustrated by experiments, demonstrating, that all of them from GEBER to STAHL had been deluded by one and the same error … His other proposal was to publish the laborious experiments [that] he had prosecuted many years on metals, particularly mercury.Footnote 68

Undoubtedly, Boerhaave's long work and his conclusions on mercury contributed to his fame and brought about profound changes in the chemistry of the eighteenth and nineteenth centuries. The Royal Society would publish his memoirs on mercury again in the nineteenth century and they would be praised as a step forward in chemistry for marking the end of the alchemical view of the transmutation of metals. However, the correspondence with Bassand shows that Boerhaave himself continued to believe in the existence of a metalliferous prime matter until the end of his life.

Gur in its modern meaning

Forty years after Boerhaave wrote these letters to Bassand, ideas on Gur and its qualities gained a modern outlook as it was reinterpreted through mineralogy. In the Eléments de minéralogie docimastique, for example, Balthazar Georges Sage defines ‘Guhr’ or ‘fluid chalk’ simply as ‘water mixed with chalk’.Footnote 69

Gur still deserved a place in the dictionary of the German language prepared by the brothers Grimm from 1854 onwards, where once again Mathesius was quoted as the source of the word. Also, the Grimms made a philological genealogy of the word up to the current form Kieselguhr. Here Gur was defined as a pasty, earthy fluid, with the term still in use by miners at the time.Footnote 70

A sample of Gur was once held at the Museum of Natural Science of the Humboldt University of Berlin. In the identification of this substance, the role of Martin Klaproth was crucial. Besides Gur, sixteenth-century miners, especially from the region of the Harz Mountains, spoke about a ‘buttermilk-earth’, namely a whitish fluid with a high silver content.Footnote 71 Klaproth subjected to chemical analysis a sample dating from 1617 (this would be the sample exhibited at the Humboldt University museum).Footnote 72 Analysis showed it to be composed of silver (24.64 per cent), muriatic acid (i.e. hydrochloric acid, 8.28 per cent) and argil (67.08 per cent).Footnote 73 On the other hand, Klaproth described as Guhr any ‘muddy, greasy substance, issuing from the clefts of the rocks’; he noted that ‘on exposure to the air it soon dried up to a very subtle, black powder’,Footnote 74 thus divorcing it from the traditional concept in the older sources.

Concluding remarks

Facing the complexity of the theories of matter emerging in the early modern period, one can ask what the relevance might be of studies on simple materials such as Gur. However, by studying this seemingly simple material from several historical perspectives, it has been possible to highlight and illuminate some aspects that otherwise would have remained in the shadow.

In the first place, Gur was sought and discussed in changing contexts throughout the three centuries covered by our study. More specifically, we focused on the connections within and among different groups, whose particular interests did not necessarily converge. Nevertheless, it was possible to see how individuals belonging to such disparate fields as mining, religion, natural philosophy and medicine, without trespassing the boundaries of their own fields of activity, elaborated intricate formulations about one and the same topic, namely a material called Gur. On the other hand, our approach did not in the least mean to neglect the conceptual aspects associated with Gur: on the contrary, they are one of the major features of this article.

To summarize, our study of Gur has helped to bring to full light some ideas on matter that were prevalent for three hundred years. More particularly, it was possible to observe that while these ideas varied significantly among the different groups over such a lengthy period of time, nonetheless they also conserved some common elements that persisted well into the eighteenth century. Such was the case, for instance, of the all-important notion of a material principle at the base of the generation of metals.

Furthermore, by following this route, we were able to find common interests and shared traits between two characters consistently depicted as antagonists by traditional readings. Boerhaave and Stahl were not as opposed to each other as has often been assumed in their way of thinking about matter; nevertheless, this convergence emerges as a subject that requires further study before any definite conclusion can be reached. At least, the case study of Gur shows that the notion of a principle of metals was very much alive in the thought of these two reputed doctors and chemists of the eighteenth century. This is just one illustration of how tracing the fortunes of apparently simple materials enables us to look closer into the origins of early modern science.

Footnotes

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. 111–112; 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. 37–40. 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. 29–35; 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 Berg, [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. 91–99, 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. 17.

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, 1908; 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, 1990.

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. 287–304.

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, 1766; 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. 107 ff. See also Knoeff, Rina, Hermann Boerhaave (1668–1738): Calvinist Chemist and Physician, Amsterdam: Koninklijke Nederlandse Akademie van Wetenschappen, 2002, p. 152.

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, 1923–1958, 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, 1977, 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. 69–86.

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, 1546; 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. 359. 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. 45.

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. 123 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. 748–749. 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. 259–263. 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. 157–159.

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

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, 1804, 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, 1801–1804, vol. 2, p. 113.

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

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