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 Alessandra Giumlia-Mair – AGM Archeoanalisi, Merano (BZ), Italy The mercury mine of Idrija in western Slovenia was the second largest in the world after the famous mine of Almadén in Spain. Extraction of cinnabar began at Idrija in the early post-medieval period and continued until the plant was closed in 1995. This paper examines the earlier (16th-18th century) developments in the extraction of mercury ores in Idrija and compares this both with the different methods of distillation of mercury employed in antiquity, and with the distillation techniques described in the 16th century by Vannoccio Biringuccio, Georg Agricola and Lazarus Ercker. Mercury, mines, Slovenia, Idrija, cinnabar, extraction, exploitation, distillation. The town of Idrija lies on the river Idrica, in a narrow valley between calcareous mountains in central Krain, near both Italy and Austria. The rocks here consist of layers of thick grey limestone plates with blackish mercury-rich veins, which still yield shiny drops of native mercury. Idrija is the only mercury mine in the world which contains sufficient native mercury for mining, and the town is located on the second richest mercury ore deposit yet found, from which more than 150,000 tons of mercury were extracted over five centuries. This ore deposit is 1,500 m long, 300-600 m wide and 450 m deep. There are over 700 km of mine galleries, some as deep as 420 m below the surface. Overall the mine has contributed around 13% of global mercury production, and its mercury was also one of the purest (at 99.99%) of any mercury mines. Nevertheless, this important mine has almost been forgotten by scholars working in the field of ancient metallurgy. Part of it is now a museum, but its history is not widely known. According to local legend, mercury was discovered in Idrija in 1490 by a tub-maker who was soaking his wooden containers in the spring which is now under the Trinity Church in Idrija, and found droplets of the liquid metal inside one of the buckets. It is said that the man went to a goldsmith in nearby Loka to find out what the shiny droplets were and tried first to keep the place of discovery secret, after discovering how precious this substance was, but digging alone in the mine was too heavy a task. One account has it that Cazian Anderlein, a cart-maker, gained his confidence and that they extracted the mercury ores together before selling the mine to a group of people (1). But according to another source, Cazian Anderlein was the head of a group of German miners which arrived in Idrija to work in the mine. Either way, people then began to settle in the valley and to dig out the ore. It is said that on one Saint Achatius day (22nd of June), after a period of bad luck, the miners discovered the richest vein of cinnabar ever found, just next to the main shaft (called the Antonius shaft, after the saint who protects the miners from mining accidents). Thereafter Achatius also became the saint protector of the miners of Idrija, together with the more classical Saint Barbara.  /%
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 The mine first appears in documentary sources in 1510, when Idrija was conquered by the Republic of Venice, and recaptured in the same year by Emperor Maximilian I von Habsburg. The castle of Idrija with its four towers was built at this time to defend the site, and was later used as the mansion of the governor who looked after the mine. In 1554 the importance and demand for mercury were greatly increased by the discovery in America of the amalgamation or ‘patio’ process which involved the use of mercury in the extraction of silver and gold. The mercury employed for the extraction of silver in America was mainly supplied by the mine of Huancavalica in Peru; however, some mercury was also imported from the European mines of Almadén and Idrija. By the late 18th century Idrija was supplying 10-12 thousand quintals (450-550 tons) of mercury per annum to the Spanish, ultimately to be used at Potosí (26). In 1575 Carl, Archduke of Austria and Duke of Carinthia and Krain, sent his deputy Hans Kitzling to Idrija to take over the mine and thus it became one of Carl’s personal properties. In 1580 Archduke Carl set down rules for the mine and in 1596 the deep St. Barbara shaft was sunk. According to one report, in 1736 a court committee, with Baron von Kempfen as chairman, was appointed to oversee the development of the mine. At this time the Kaschinzi shaft was dug out, the galleries widened and made secure, and structures for washing, sluicing, crushing and grinding the ore were built. The court now also began to give money to the widows of miners and mine officers. Between 1738 and 1748, the mine captain Berghauptmann Poll, who at the time was still only foreman, dug out the important St. Theresia shaft. The mines of Idrija are mentioned in several Renaissance texts, for example in the Mundus Subterraneus of Athanasius Kircher, and in the Actis anglicanis of the year 1665. Caesalpinus writes: foditur mercurius in monte Hydria prope Goriziam (mercury is extracted from the mountain of Idrija, near Gorizia). Moscardus mentions in a very similar entry: Minium nativum montis Hydriae non procul Gorizia (native cinnabar of the mountain of Idrija, not far from Gorizia). In this passage cinnabar (or vermilion, i.e. sulphide of mercury) was confused with red lead, as happens also in the well known passage by Vitruvius in the work De Architectura (7.8.1-4). König calls the metal Jungferquecksilber (virginal mercury, i.e. native mercury), and adds that it was found by Tollius near Idrija, in Carinthiae at Fori Julii confiniis (in the territory of Carinthia and Friuli) (1). Cinnabar was used very early as the bright red pigment vermilion. The most ancient known European cinnabar mine is at Šuplja Stena, on Mt. Avala in Serbia, dated to the Eneolithic Kostola! culture (2). Vasi! and Durman also suggested that the furnaces found at the famous site of Vin!a, only 20 km away, were used for smelting cinnabar (3, 4). Evidence for the early use of mercury as a metal is scanty, the earliest known piece of mercury gilded bronze being a bronze fitting, dated Late Bronze Age, from an excavation at Rathgall in Ireland (5). However, the Irish Bronze Age is very long, with the Late Bronze Age spanning the 9th to the 4th centuries BC. The Rathgall find is dated about 6th century BC. Slightly later finds of mercury include one from Al Mina in Syria and another from Seleucia, both dated 5th century BC (6), but overall little is known of the early use of mercury. Dioscorides (7) mentions Libya as the place of origin of better quality and more expensive cinnabar, although the most important mercury mines in antiquity were the Cilbian Fields of Ephesus, in western Anatolia, and the famous Almadén mines in Spain. There was also cinnabar of lesser quality in Colchis, in Carmania and in Ethiopia (8, 9, 10). Vitruvius also reports that the ore found in Spain was brought to Rome and dealt with by the publicani in the workshops between the temples of Flora and Quirinus.  /%
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 In a common furnace, metals with a low melting and boiling temperature, such as mercury, arsenic and zinc, will decompose and volatilise up the chimney as vapour. To be recovered and employed, they have to be either used directly in the form of ore to produce an alloy by cementation with another metal (as it was the case in antiquity with arsenic and zinc), or to be distilled, as in the case of mercury. Mercury boils at 357° C, and cinnabar, burnt in the presence of oxygen, breaks down and gives off mercury vapour at 600-700° C. Ancient distillation processes are known, for example in the production of perfumes (11, 12), and occur in Alexandrian chemical texts with various examples of the application of aludels (condensers) combined with alembics (stills – see Fig. 1) (13). Pliny also mentions a method to recover pitch from pine wood by putting it into a vessel and heating it all around in an oven: the liquid which exudes from the wood flows “like water” down a pipe (14). Fig. 1: Illustration from the S. Marco manuscript with the representation of a distillation apparatus, i.e. a dibikos (an alembic with two beaks) and two receivers on a hearth (from Berthelot 1888). The earliest description (15) of the distillation of cinnabar is in the Materia Medica (!"#$ %&'( $)*#$+'(), written in the 1st century AD by a Cilician-Greek, the physician, pharmacologist and botanist Pedanius Dioscorides, born in Anazarbos in Asia Minor. Dioscorides’ text says: Putting an iron bowl containing cinnabar in a clay vessel, they cover it with a helmet [-shaped vessel] smearing it with clay, then they heat it with coals; the soot which adheres to the vessel, becomes mercury when scraped off and cooled (transl. Giumlia-Mair). This description is repeated almost word for word by Pliny (16) who adds: the cleaned condensed liquid which becomes the colour of silver and [has] the fluidity of water,...is also divided into drops and runs down like a slippery liquid. Pliny also makes a distinction between native mercury (argentum vivum) and mercury obtained by distillation from cinnabar (hydrargyrum). Vitruvius’ description of the extraction of mercury from cinnabar is generally good (except for the confusion with minium: red lead oxide): Now I will proceed to explain the treatment (or production) of minium (here vermilion, a processed form of cinnabar, sulphide mineral of mercury). The material, which is called ore, is dug up, then they produce minium by treating it. In the veins the ore  /%
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 is like iron, more ruddy in colour, and having reddish dust around it. When it is dug up and beaten with iron tools, it exudes many drops of mercury, which are collected quickly by the miners. Once this ore has been collected in the workshop it is placed in a furnace to dry because of its large amount of moisture. Next, when the steam stirred up by the heat of the fire condenses on the floor of the furnace, it is discovered to be mercury. After the ore is taken away, the drops which remain because they are too small to be collected are swept together into a container of water where they run together and are combined into one mass. When they are weighed, four sextarii [equivalent to 2.3 l] of mercury come to 100 librae [32.5 kg]…. Mercury, moreover, is useful in many instances. For neither silver nor brass can be properly gilt without it. And when gold is embroidered in clothing and the garment, worn out with old age, has no decent use, the cloth is put into a clay vessel and burnt over the fire. The ash is thrown into water and mercury is added to it. The mercury then gathers all the particles of gold onto itself and combines with them. Once the water is poured off, the remainder is spread over a cloth and pressed by hand. The mercury, since it is liquid, passes through the texture of the cloth when forced by the pressure, and pure gold is found in the cloth. (Transl. Humphrey et al. 1998, 214) (29). Fig. 2: Distillation of mercury from the book Pirotechnia of Biringuccio. The double pot. Fig. 3: Distilling bells from Biringuccio’s Pirotechnia.  /%
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 The simple methods described by Dioscorides, Pliny and Vitruvius were in use from antiquity to the Renaissance, when several sources describe contemporary processes, the earliest (published posthumously in 1540) being in De la Pirotechnia of Vannoccio Biringuccio from Siena (17, 18). Biringuccio describes a chamber for the condensation of distilled mercury vapour, and his long explanation is repeated almost word for word by Agricola. In the Pirotechnia there are both detailed accounts and representations of several methods, which go from the large earthenware pots of different shapes put together mouth to mouth to distil the vapour from the ore and collect the mercury (Fig. 2), to the more sophisticated distilling bells, provided with long beaks (Fig. 3) through which the mercury droplets run down and are collected in other vessels (or receivers). In the treatise De re metallica published in 1556, Georg Agricola describes the same methods, but also the more productive application of destillatio per descensum (Fig. 4) by which the ore was distilled in double pots in a roasting hearth in which as many as “seven hundred pairs of pots” could be set together (19, 20, 21, 31). Fig. 4: Illustration from the book De re metallica of Georg Agricola, 1556. Destillatio per descensum. In the Probierbüchlein, Lazarus Ercker mentions the use of mercury for the recovery (22) and purification of gold (23). Furthermore, there is also a chapter on the recovery of gold “when there is no mercury”, giving an idea of the price and rarity of this metal. A later chapter is on the separation of gold and mercury and the subsequent treatment of mercury “which is not as strong as it was before and looks rather dull”, and which therefore had to be purified before being used again (24). The famous Renaissance scholar Aldrovandi mentions the mercury mine of Idrija in several passages of his Musaeum Metallicum. In particular he reports a sentence of Ortelius in the work Theatrum Mundi in which mercury is listed under the products of the region Friuli (Forum Iulii). Most interesting in the section dedicated to mercury is the entry on the methods of extraction and preparation of mercury (25). Aldrovandi describes how the prospectors look for mercury ores and lists different ways of smelting. As was the case with Biringuccio and Agricola, the choice of words  /%
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 he employs is strongly reminiscent of the ancient Greek and Latin texts. For example he gives an account, very similar to that of Pliny, on how “after collecting the ores, to avoid the poisons of mercury the miners covered their mouths with a thin skin obtained from animal bladders and crushed and ground the minerals. Then they put them into clay vessels and placed another bellshaped vessel on top of it, so that the mercury went up into the bell-shaped vessel and dripped into the collecting vessel” (transl. Giumlia-Mair). Between 1754 and 1769 the scholar Johannes Antonius Scopoli (1723-1788), a physician and naturalist from Cavalese in Val di Fiemme (at the time part of the Austrian Empire) and a pioneer in the field of modern medicine, became the first physician of the mine of Idrija. During his time in Idrija he wrote most of his many works while in correspondence with the famous Swedish botanist, physician and zoologist Carl von Linne. Scopoli’s 30 odd volumes on botany, geology, mineralogy, chemistry and medicine included a book titled De Hydrargyro Idriensi (On Idrija’s mercury). In his Tentamina Physico-Chimico-Medica, printed in Venice in 1761, he discussed mercury ores and mercury, the mineral epsomite (vitriol) from Idrija and mercurialismus, i.e. the poisoning of the miners by mercury vapours (30). After his experience in Idrija he became professor of chemistry, mineralogy and metallurgy at the Mining Academy in Schemnitz (Banská Štiavnica in Slovakia) and later at the University of Pavia. The amalgamation of silver ores was first recorded in Venice in 1507, when former goldsmiths Tommaso Cusano and Giovanni Antonio Mauro received permission to extract silver from the ore by using mercury and water, instead of fire, most probably using mercury from Idrija (1). Between 1551 and 1553, Bartolomé de Medina applied the amalgamation method (by then discussed by Biringuccio in books 1 and 3 of the Pirotechnia) to the silver ores at Pachuca in Mexico, and the new discovery led to a huge increase in the world demand for mercury. In 1559 the Spanish Crown officially acknowledged Bartolomé de Medina as the inventor of the beneficio de patio (yard beneficiation) and the process spread from Pachuca to Potosì, Zacatecas, Guanajuato, Fresnillo, Mazapil, Chalchihuites and all over the Spanish Empire (27, 28). In 1774 J. Ferber reported that the first distillation process in use at Idrija had been the “per descensum, described by Georg Agricola, Ercker and Fallopius”, with two clay containers put mouth to mouth on top of each other, indeed the same process described and illustrated by Biringuccio (Fig. 2). Traces of this process were still recognizable in the woods around Idrija more than 200 years later when they were noticed by Ferber, whose volume – the most important text on the mercury deposits of Idrija – contained all the information that he was able to collect on the mine at that time (1). Between 1557 and 1635 the method employed to smelt the ores involved the use of clay condensing vessels put into a furnace (Fig. 4). This was apparently the process represented in the most famous illustration of the distillation of mercury in the book De re metallica by Georg Agricola, in which a large number of sealed double pots (or retorts) are placed into a hearth, and surrounded by earth and charcoal so that only the upper pot is visible. Wooden beams are placed over and between the condensing vessels and fired. The ceramic used for this process had to be of the finest quality, to avoid breakage during firing, with subsequent loss of valuable mercury vapour. The smelters had to stand with their backs to the wind, to avoid the poisonous fumes, and the building in which the hearths were built had to be open around the front and sides.  /%
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 Johann Friedrich Stampffer, Baron of Walchenberg, reported in 1715 that, by 1635, the process had already been greatly improved by the experiments of a chemist, who introduced the use of more robust cast iron condensing vessels (Fig. 5). Fig. 5: Discarded cast iron condensers in Idrija. (Photo A. Giumlia-Mair). In 1696 a further improvement of the process was introduced by Lorenz Wörath, a member of the court commission of Idrija, who suggested the addition of quicklime to the charge. At about the same time the cast iron condensing vessels were replaced by wrought iron containers. Subsequently, in 1715, Stampffer introduced this kind of condensers into the German mercury plants of the Palatinate and of Zweibrücken in Saarland. An important innovation, introduced to Idrija in 1750 by Berghauptmann Poll, were the so-called Spanish furnaces for the distillation of mercury, invented in 1633 at Huancavelica by Lope de Saavedra Barba and brought to Almadén (Fig. 6) by Juan Alonso de Bustamante in 1646 (26). Fig. 6: The roof of the furnaces at Almadén in Spain with the four groups of 8 rows of condensers. Compare with Figs. 7-8-9. (Photo L. Morejòn). In Idrija the system was further perfected by the smelting master (Oberbrennmeister) Pasezky, who managed to reduce mercury vapour loss from the chimneys by making several technical improvements (see below).  /%
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 The low grade ore in Slovenia is still called bašperh, i.e. low mineral, while the best ore is known as jeklenka (steel ore). Bašperh combines the Italian word ‘basso’ (low) and the German word ‘Berg’ (mountain, or in this case rock), thus reflecting the different languages and mixed origins of the people who worked in the mine, and the complex history of this area. The distillation plant discussed by Ferber consisted of a system with a double furnace in which the fire was separated from the ore by a perforated vault. Wood was used as fuel and the smoke of the fire burning in the vaulted furnace went up a side-chimney and was dispersed (Fig. 7). The ashes could then be removed through a low opening in the wall. Ore was put into the upper chamber of the furnace as follows: larger pieces of low grade ore formed the lowest layer; the second layer consisted of smaller pieces of better ore (Fig. 8). Bricks made of powdered ore mixed with clay were then piled on top of the layer of low grade ore. The charge had to fill up the chamber so that only one foot of space remained free. The smoke mixed with sulphur and mercury vapour was collected in the upper part of the furnace and passed into six rows of connected condensers made of special refractory clay which, in the contemporary texts, are commonly referred to as aludels (condensing or sublimation pots). These condensers lay on an inclined terraced roof in the lower middle part of the building. In the middle of the roof there were two channel-shaped hollows that collected the mercury coming out of the aludels which were at the lowest point of the terrace (Fig. 8). The condensers in the hollow were the only ones showing an opening from which the condensed mercury could drip out into the channel and from there run into the holes in the centre of the terrace. The mercury flowed down a pipe into a water basin where it collected on the bottom (Fig. 9). Fig. 7: The ‘Spanish’ plant at Idrija was introduced and perfected by Berghauptmann Poll in 1750 (from Ferber 1774). The remaining vapour flowed up the aludel rows into the ‘smoke chamber’ on the other side of the building (Fig. 8). Here the heavy fumes were driven down the walls by a partition and the  /%
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 condensed mercury was collected in a water basin. The rest of the fumes went up into the smoke chamber. The mercury deposited on the walls here dripped down and was collected in a hollow in the floor. The narrow internal chimney of the smoke chamber was covered with a metal ‘hut’ which allowed faster cooling and condensing of the vapour. Fig. 8: Vertical section of the ‘Spanish’ plant in Idrija. The furnace and the ore reduction chamber are visible on the left, the smoke chamber on the right (from Ferber 1774). The fumes passed through a small opening in the ‘hut’ and reached the highest part of the two smoke chambers. Here, some of the remaining mercury was collected in the space under the roof and in the gutter under the two windows, which could be opened or closed as needed during the different phases of the process and depending on the outside temperature, the weather and the wind. Ferber stated that with this kind of furnace it was quite difficult to establish a regular weight for the charge, because the treated ores were not of homogeneous quality. The volume of ore in the furnace was always the same, but the weight could change according to the quality of ore which was being distilled. The firing with wood lasted 5 or 6 hours, then the charge burned by itself and the smelting took 3 to 4 days. At the end the fire was allowed to burn out and the system left to cool down for 5 to 6 days before the breaking out of all openings which previously had been carefully bricked up. After the description of the system and the process Ferber also suggested several possible improvements, such as the use of pipes instead of aludels to avoid the loss of vapour, and the addition of devices for cooling the smoke chamber and recovering more mercury. Fig. 9: Plan of the ‘Spanish’ plant in Idrija: the roasting bed and the floor of the furnace are visible on the left, with the 12 rows of aludels positioned on the inclined terrace (from Ferber 1774).  /%
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 The millennia long history of the distillation of mercury is still not well known and much more research is necessary to retrieve the details of the different stages of its development. The study of the distillation techniques employed in the mercury mine of Idrija is only one part of what needs to be done. This research has shown that even in large mines such as Almadén and Idrija, in which similar systems were used, the details of the local processes were different, because they were continuously developed and diversified through the introduction of a series of improvements and innovations. Improved systems were sometimes ‘exported’ to other plants, as happened with the wrought iron pots, which were introduced both in the mines of the Palatinate and in Zweibrücken in Saarland. Even where improved systems and new equipment were introduced, the old apparatus did not always cease to be used. For instance at Idrija, when the ‘Spanish’ plant was built the wrought iron pots (Fig. 5) were not abandoned, but were subsequently employed in the assaying of the ores. After five centuries of operation the mercury mine of Idrija was finally closed in 1995, a result of the decreasing demand for this metal, largely because of the high toxicity of mercury and most of its compounds. Increased health and safety regulations have brought about the progressive reduction of the industrial employment of mercury and from 2011 the trade in these substances will be banned from the entire area of the European Union. Very recently, in 2007, Idrija was suggested for nomination on the world heritage list, together with Almadén, Huancavelica and San Luis Potosí, as one of the most important centres on the Mercury route of the Intercontinental Camino Real. Further detailed work on the different extraction methods, the structure of the galleries and shafts and the various beneficiation plants used in Idrija is planned for the future. Special thanks are due to Dr Daniela Peraldo of the Museum of Natural History of Trieste for the invaluable help with the archive research and the documentation on the Idrija mines. 1) J.J. FERBER, Beschreibung des Quecksilberbergwerk zu Idria in Mittel-Krayn, (1774) Ch.F.Himburg, Berlin. 2) V.MILOI!I!, 1943, Das vorgeschichtliche Bergwerk „Šuplja Stena“ am Avalaberg bei Belgrad in Serbien, Wiener Prähistorische Zeitschrift XXX, 41-54. 3) M. VASI!, 1932, Preistorijska Vin"a I, Industrija cinabarita i kosmetika u Vin"i, Beograd. 4) A.DURMAN, The Neolithic settlement in Vin"a, IAMS Newsletter, (2002), Institute for Archaeometallurgical Studies, London. 5) R.F.TYLECOTE, The Early History of Metallurgy in Europe,(1987), Longman, London, 43. 6) P.T.CRADDOCK , Early Metal Mining and Production, (1995) Edinburgh University Press, Edinburgh, 302 7) DIOSCORIDES PEDANIUS, Materia Medica, 5, 94. 8) VITRUVIUS, De Architectura, 7, 8. 9) PLINIUS, Naturalis Historia, XXXIII,111-124. 10) A. HAUPTMANN and R.SLOTTA, Der Anschnitt, 31, (1979), Bochum, 81-100. 11) E.EBELING, Parfumrezepte und kultische Texte aus Assur, (1950), Opera, Rom.  /%
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 12) FORBES R.J., A short history of the Art of Distillation (1940), Brill, Leiden 13) M.BERTHELOT, Collections des anciens alchimistes grecs, réimpr. éd.1888, (1967), O.Zeller, Osnabrück, vol.1, 127-165. 14) PLINIUS, Naturalis Historia, XVI, 52. 15) DIOSCORIDES PEDANIUS, Materia Medica, 5, 95, s.v. hydrargyros. 16) PLINIUS, Naturalis Historia, XXXIII, 123. 17) V. BIRINGUCCIO, De La Pirotechnia 1540, Edizioni il Polifilo (1977), Milano. 18) V. BIRINGUCCIO, Pirotechnia, (1540), the MIT Press, (1966), Cambridge Mass. London. 19) G. AGRICOLA, De l’Arte de Metalli, (1563), Froben, Basilea. 20) G. AGRICOLA, De re metallica, (1556) orig. Latin version, Minerva Verl. (1991) Frankfurt. 21) G. AGRICOLA, Zwölf Bücher vom Berg- und Hüttenwesen, (1978), VDI Verl., Berlin. 22) L.ERCKER, Das Grosse Probierbuch 1580, Beschreibung der allervornehmsten mineralischen Erzen und Bergwerksarten vom 1580, (1960), Freiberger Forschungshefte, Kultur und Technik D34 Akademie Verlag, Berlin, Buch II, 121-123. 23) L.ERCKER, s. above 22), 124, fig.17. 24) L.ERCKER, s. above 22), 124-125. 25) U. ALDROVANDI, Musaeum Metallicum in libros III distributum, I.B.Ferronii ed., (1648), Bologna (Bononia), I, 199. 26) A.P. WHITAKER, The Huancavelica Mercury Mine, (1971), Greenwood Press, Westport, Connecticut, 64. 27) M. BARGALLÓ, La amalgamación de los metales de plata en Hispanoamérica colonial. (1969) Mexico D.F., Compa!ía fundidora de hierro y hacer de Monterrey , 29-30. 28) A. CARRILLO, Tratado curioso. Descripción breve de las antiguas minas de Espa!a, in: Arte de los metales, de Álvaro Alonso Barba, (1977), Riotinto, Huelva, Unión Explosivos Riotinto, 219-225. 29) HUMPHREY J.W., OLESON J.P., SHERWOOD A.N., Greek and Roman Technology: A Sourcebook Annotated Translations of Greek and Latin Texts and Documents, (1998), Routledge, London. 30) SCOPOLI J.A., Tentamina Physico-Chimico-Medica, 3 volumes, (1761), Venice. 31) G. AGRICOLA, De re metallica, (1556) Hoover H.C. & Hoover L.H, (1950) Dover Publ., New York. 32) G. AGRICOLA, De re metallica, Libri XII (1556), Zwölf Bücher vom Berg- und Hüttenwesen, (repr. 1928), Fourier Verlag/VDI-Verl., Berlin.