This is the text of a paper published in JOM (Journal of Metals) in the January 2000 issue, p. 12-13. The published version has an overlay illustration that shows mercury distillation from Vannucio Biringuccio’s "Pirotechnia", first published in 1540.

Laszlo Takacs

Theophrastus’ book "on Stones", written in the fourth century B.C., is the earliest known work on minerals, their properties, and applications. The book is full of interesting information compiled in a clear, easy-to-read style. The excerpt examined in this article is especially important, as it represents the first known mechanochemical reaction, as well as the first description of any process for obtaining a pure metal from a compound.

Mechanochemistry applies mechanical energy - in the form of rubbing, grinding, milling, etc. - to bring about chemical reactions. Some mechanochemical effects are quite intuitive. For example, the dissolution of salt or sugar can be accelerated by prior grinding. Such mechanochemical effects have been utilized by mankind since prehistoric times.

The written history of mechanochemistry is much shorter. M. Carey-Lea published two papers about the decomposition of silver and mercury halides in 1892-94 [1]. Most historical reviews mention those papers as the first examples of a mechanochemical reaction [2-4]. However, in the mercury section of Zvi Goffer‘s "Archaeological Chemistry" [5], he mentions an ancient mode of preparation as a curiosity: "Native cinnabar (mercuric sulfide, HgS) was rubbed with vinegar in a copper mortar with a copper pestle yielding the liquid metal." This is a very clear description of a mechanochemical process. The source of the information is given as Hill’s "Theophrastus’ History of Stones" [6], a 1774 English translation of Theophrastus’ Greek original written at the end of the 4^th century B.C. Theophrastus’ History of Stones is the earliest preserved text on any subject related to chemistry or metallurgy. Therefore, the sentence on the preparation of mercury is very probably the earliest reference to any mechanochemical reaction, extending the documented history of the process by more than two millennia.. As such, it deserves a careful look.

Theophrastus of Eresus (371-286 B.C.) was a student of Aristotle and his successor as the head of the Lyceum in Athens from 322 B.C. until his death. His book "On Stones" or "De Lapidibus" is the earliest surviving scientific book on minerals. In fact, it is also the first book on any subject related to metallurgy or chemistry. It was written close to the end of the fourth century B.C., most probably during 315-314 B.C. [7]. The book consists of 69 paragraphs, written in a clear, concise, and informative style. The sentence on the preparation of mercury can be found in paragraph 60.

Three English translations are available. The earliest one is Sir John Hill’s work, first published in 1746, the second edition followed in 1774 [6]. His translation of the sentence on the preparation of quicksilver (mercury) reads: "This is obtained from native Cinnabar, rubbed with Vinegar in a brass Mortar with a brass Pestle." Hill’s translation of "On Stones" is supplemented by valuable commentary that reflects broad knowledge of the sciences and technology of his time. He remarks: "We have now many Ways of extracting the Quicksilver from Cinnabar, but all by the Assistance of Fire" [8]. This statement suggests that, by the middle of the 18^th century, the mechanochemical decomposition of cinnabar was no longer applied in metallurgical practice.

The second English translation of "On Stones" was published by Caley and Richards in 1956 [9]. Their translation is somewhat more wordy: "It is made when cinnabar mixed with vinegar is ground in a copper vessel with a pestle made of copper." The most significant deviation from Hill’s version is the mention of copper grinding tools rather than brass. Copper is indeed more likely, as brass was rarely used in antiquity. The commentary of this translation is also rich in valuable information. It states that Theophrastus’ note on the reduction of cinnabar is "the earliest description of any method of isolating a metal from one of its compounds." Consequently, this record is of great historical significance also for extraction metallurgy.

The linguistically most careful translation was prepared by Eichholz [10]. It states that quicksilver "... is made by pounding cinnabar with vinegar in a copper mortar with a copper pestle."

Theophrastus put much emphasis on the effect of fire on rocks. In fact, he classified rocks based on their behavior when heated [11]. Yet, he found the making of mercury by rubbing important and interesting enough to record. As mentioned earlier, however, this classic mechanochemical process was forgotten before Hill prepared the first English translation in the middle of the 18^th century. It is interesting to look for traces of the method in the literature during the intervening time. Much of our knowledge on ancient and medieval science originates from encyclopedic works that summarize information from earlier works (usually without mentioning the source) and extend it with new discoveries. Therefore, it is anticipated that the mechanochemical preparation of mercury is restated in the later literature, following the description given by Theophrastus.

Vitruvius wrote about cinnabar and quicksilver in the late 1^st century B.C. [12]. His sources are obviously different, as he does not mention the method or Theophrastus. However, he does mention the decomposition of cinnabar by both mechanical action and heating. He makes a vivid remark about the mining of cinnabar: "During the digging it sheds, under the blows of the tools, tear after tear of quicksilver." This mode of decomposition does not require the presence of any other reactant. This method is still a mechanochemical process, but different from the one described by Theophrastus.

The Natural History by Pliny (Caius Plinius Secundus, 23-79 A.D.) is an important link, as it describes the preparation of quicksilver by both mechanochemistry and distillation [13]. The first one is a reproduction of the method of Theophrastus, probably directly copied from "On Stones." The method of distillation apparently originates from Dioscorides: The cinnabar is heated in an iron shell, decomposes and the resulting quicksilver condenses onto a convex lid. The product is collected by wiping it off from the lid [14].

For the next 1500 years, nothing significant was written about the extraction of quicksilver [14], although the technical details of the distillation process certainly improved. The next important work, "Pirotechnia" by Biringuccio (1540) describes the distillation process only [14].

The most important work on mining and metallurgy after Theophrastus and Pliny is Agricola’s De Re Metallica [15]. It is a comprehensive (640 folio pages) treatise that was the primary source of information on the subject for centuries. If the mechanochemical decomposition of cinnabar had been known and practiced in that time period, De Re Metallica would probably mention it. A careful search of the appropriate sections turned up no result. Agricola describes five different arrangements for the smelting of mercury from cinnabar by fire, but there is no mention of the mechanochemical process [16]. This is somewhat surprising, as Agricola was probably familiar with the works of Theophrastus and Pliny. A probable reason is that De Re Metallica is a practical guide on the engineering and even the economics and law of mining and metallurgy. It describes methods for actual engineering practice, methods that can be applied on a large scale with economic benefit. The decomposition of cinnabar by rubbing in a mortar is not feasible as an industrial process.

De Re Metallica was translated to English by Herbert C. Hoover, an international authority on mining and metallurgy himself (and later the 31^st president of the United States) together with his wife, Lou Henry Hoover, an excellent geologist herself. The translation was the product of five years of careful work [17]. Just like the translators of "On Stones," they supplemented the text with extensive and informative footnotes. One of them is a list of 45 important metallurgical processes with the times of their invention. The 17^th of them reads: "Mercury reduced from ores by (?), prior to 400 B.C." [18]. This question-mark is the last faint hint in the technical literature that the ancients had some unusual method to derive mercury from cinnabar. This is the only question-mark in the list, every other item is clearly defined.

It is worth emphasizing that translating De Re Metallica was a very difficult task that required language skills as well as accurate understanding of the subject. The Hoovers and their associates often consulted other sources to clarify uncertain points or even performed laboratory experiments to make sure that Agricola’s text was not misinterpreted [17]. Yet, they left this problem unresolved. We may never know the reason for sure. Probably the list was compiled by an associate without sufficient time to research all the details. This can be inferred from the fact that the list contains other inaccuracies: The quoted time of discovery is one century too old. As "On Stones" was written close to 300 B.C., there seems to be no proof that the process had been known 100 years earlier. The 20^th item on the same list is "Quicksilver reduced from ore by distillation, prior to Christian Era." The naming of the metal is inconsistent here, as the modern name, mercury, was used just three lines earlier.

It remains a mystery why the mechanochemical preparation of mercury from its sulfide was forgotten during the middle ages. It is not that mercury was unknown or unimportant. Alchemical theory stated that "the proximate constituents of all metals are known to be sulphur and mercury" [19]. While this is clearly not the view of modern chemistry, the central role of mercury and sulfur in alchemy resulted in solid knowledge about their particular properties. As Bonus writes, "though when mercury and sulphur are heated together cinnabar is formed, yet on further heating the mercury is regained pure and clean." [20]. This is a very accurate description of the thermochemical formation and decomposition of cinnabar. Yet, the mechanochemical behavior of the same chemical system does not show up in alchemical writings. Alchemists considered fire the general means of purification, and rubbing was not considered a possible alternative.

Examples of other mechanochemical reactions documented between 300 B.C. and the end of the 1800s are mentioned in Agricola’s "De Natura Fossilicum" [21]. He writes about "the artificial minium the painters call cinnabaris... This material, when pulverized, sparkles as though it had been adulterated with mercury." He also mentions grinding with a chemical in relation to the preparation of "artificial chrysocolla:... The fine mineral is ... macerated with vinegar until it becomes soft. It is again ground in a mortar and then washed in shells and dried." In another case, grinding with vinegar or wine is mentioned as one step in a complex process [24]. Although these processes do represent chemical effects of mechanical action, they are inferior examples compared to the preparation of mercury as described by Theophrastus. There may exist other mechanochemical reactions in the early literature. In particular, this search was restricted to Western science; relevant discoveries could also be made in India or China.

Theophrastus’ book "On Stones" is the earliest known work on minerals, their properties, and applications. It is a gem, full of interesting information, compiled in a clear, easy-to-read style. The sentence examined in this paper is especially important, as it represents the first known mechanochemical reaction, as well as the first description of any process for obtaining a pure metal from a compound.

[1] M. Carey-Lea, Phil. Mag. 34, 46 (1892) and 37, 31 and 470 (1894).

[2] G. Heinicke, Tribochemistry, Akademie Verlag, Berlin, 1984.

[3] E. G. Avvakumov, Mechanochemical Methods of the Activation of Chemical Processes, Nauka, Novosibirsk, 1986.

[4] A. Z. Juhasz and L. Opoczky, Mechanical Activation of Minerals by Grinding, Akademia Kiado, Budapest, 1990.

[5] Zvi Goffer, Archaeological Chemistry, A sourcebook on the Applications of Chemistry to Archaeology, John Wiley & Sons, New York, 1980, p. 208.

[6] J. Hill, Theophrastus’ History of Stones, London, 1774, p. 235.

[7] Theophrastus, De Lapidibus, Translation and Commentary by D. E. Eichholz, Oxford University Press, 1965, p. 8.

[8] Ref. 6, p. 232.

[9] E. R. Caley and J. F. C. Richards, Theophrastus on Stones, The Ohio State University, Columbus, 1956, pp. 58 and 204.

[10] Ref. 7, p. 81.

[11] G. Sarton, A History of Science, Ancient Science Through the Golden Age of Greece, Harvard University Press, Cambridge, 1960, p. 560.

[12] Vitruvius, The Ten Books on Architecture, translated by M. H. Morgan, Dover Publications, New York, 1960 (original publication by Harvard University Press, 1914) Book VII, Chapter viii, paragraphs 1 and 2 (p. 215).

[13] Pliny, Natural History, translated by H. Rackham, Harvard University Press, Cambridge, Massachusetts, 2^nd ed., 1961, Vol. IX, Book XXXIII, 123 (p. 93).

[14] L. J. Goldwater, Mercury, A History of Quicksilver, York Press, Baltimore, Maryland, 1972, pp. 49-53.

[15] Georgius Agricola, De Re Metallica. Translated from the first latin edition of 1556 by Herbert Clark Hoover and Lou Henry Hoover. The Mining Magazine, Salisbury House, London, 1912.

[16] Ref. 15, pp. 227-231.

[17] George H. Nash, The Life Or Herbert Hoover. The Engineer, 1874-1914, W. W. Norton and Comp., New York, 1983, pp. 480-495.

[18] Ref. 15, p. 354.

[19] E. J. Holmyard, Alchemy, Penguin Books Ltd. Harmondsworth, Middlesex, England, 1957, p. 146.

[20] Petrus Bonus, The New Pearl of Great Price (Pretiosa Margarita Novella), about 1330, as quoted by Holmyard [19] p.146.

[21] Georgius Agricola, De Natura Fossilicum (Textbook on Mineralogy.) Translated from the first latin edition of 1546 by Mark Chance Bandy and Jean A. Bandy, The Geological Society of America, New York, 1955.

Laszlo Takacs is Associate Professor in the Department of Physics,

University of Maryland, Baltimore County

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