The history of mercury. From discovery to incommodity

Mercury is present in the world in very small amounts, but it has played a very important role in the development of alchemy, extraction of gold and silver, in the chloro-alkali industry, batteries, construction of scientific instruments, treatment of illnesses, and pest control. Increasing environmental concerns are leading to a significant reduction in annual production and to its substitution by alternative components. DISCOVERY OF MERCURY Archeological finds indicate that mercury has been in use for more than 2 500 years, but give no indication on how it was discovered. Arribas1 offers a simple explanation, based on chapter Mercury of Primo Levi’s (19191987) book The Periodic Table:2 “One day, after a few periods of tremors, the prehistoric man that inhabited in an open cave in a mountainous system of volcanic origin, was surprised to observe that from the cracks in the ceiling, in addition to water, another strange shiny grey liquid oozed in thick drops that on hitting the floor burst into many small drops of high mobility. After collecting some of it he noted that contrary to other liquids the new one did not wet the hands but produced a cool feeling. He also observed that the new liquid was so dense that stones, pieces of lead or of iron floated on it, and that the liquid gave a silver color to the metals.” Mercury was much discussed by philosophers in the days of Aristotle (384-322 BCE) who record its use in religious ceremonies and called it fluid silver,3 Theophrastus (371-286 BCE) mentions the deposits of the Almadén region of Spain as an important source of vermilion for use in Greece and Rome and gives a general description of the purification of cinnabar for use as the pigment, and a method of preparing metallic mercury:4 “Spanish cinnabar, which is extremely hard and strong, is natural, and so too is that of Colchis... The manufactured variety comes from one place only, which is a little above Ephesus. Here, a sand which glows like scarlet kermes-berry is collected and thoroughly pounded to a very fine powder in stone vessels. It is then washed in copper vessels, and the sediment is taken and pounded and washed again. There is a talent in doing this, for from an equal quantity of material some workers secure a great amount of cinnabar, and others little or none... The process is said to have been invented and introduced by Callias (one of the wealthiest men in Athens)... from the silver-mines, who collected and studied the sand, thinking that it contained gold owing to its glowing appearance. But when he found that it contained no gold, he still admired its fine color and so came to discover the process, which is by no means an old one, but dates back only some ninety years before the archonship of Praxibalus at Athens... Quicksilver... is made by pounding cinnabar with vinegar in a copper mortar with a copper pestle.” The extraction of mercury by roasting the ore and the property of amalgamation, have been described in detail by Roman writers. Vitruvius (90-20 BCE) wrote:5 “When the ore has been collected in the workshop, because of the large amount of moisture, it is put in the furnace to dry. The vapor, which is produced by the heat of the fire, when it condenses on the floor of the oven, is found to be quicksilver. When the ore is taken away, the drops which settle because of their minuteness cannot be gathered up, but are swept into a vessel of water; there they gather together and unite”. He adds that four sextard (a sextarius was measure of volume equivalent to 0.547 L) of mercury weigh 100 librae and that a stone, however heavy, will float on mercury, whereas even a small piece of gold will sink, and concludes, “That the gravity of bodies depends on their species and not on their volume.”6 Revista CENIC Ciencias Químicas, Vol. 39, No. 3, 2008. 148 In the first century CE, Pedanios Dioscorides (40-90 CE) of Anazarbus, Cilicia described the following process for preparing metallic mercury7: “Putting an iron spoon having Cinnabaris in an earthen pot, they cover the Cup dawbing it about with clay, then they make a fire under with coals; and ye soot that sticks to ye pot, being scraped off & cooled, become Hydrargyrum. It is found also in ye place where Silver is melted, standing together by drops on ye roofs. And some say that Hydrargyrum is found by itself in ye mines. But it is kept in glassen, or leaden, or tinnen, or silver vessels, for it eats through all other matter, and makes it run out”. Dioscorides distinguished between native and virgin quicksilver, called argentum vivum, and hydrargyrum, the name given to quicksilver prepared from cinnabar. The two were assumed to have different properties. He also pointed out that because of its red color cinnabar was sometimes confused with and at other times used as an adulterant for the red oxide of lead or minium. He prepared quicksilver from cinnabar by placing it in an iron vessel, which was then set in a clay dish; another clay dish was placed on the first as a cover, and all were luted together with clay. A charcoal fire was then placed under them and blown with a bellows. The top vessel collected a black soot that was washed for quicksilver.8 Pliny9 (23-79 CE) published the most ancient and complete description of cinnabar and vermilion: “There is also a mineral found in these veins of silver which contains a humor, in round drops, that is always liquid, and is called quicksilver. It acts as a poison on everything and breaks vessel by penetrating them with malignant corruption. All substances float on its surface except gold, which is the only thing that it attracts to itself... to separate the quicksilver itself from the gold it is poured out on to hides... and exudes through them... and leaves the gold in a pure state... Minium or cinnabar is of great importance among pigments at the present day... The most famous mine being that of Almadén... as about 2 000 pounds per year are delivered to Rome... the price of selling it being fixed at 20 sesterces (equivalent to five denarius) a pound to prevent its going beyond limit... In the cinnabar mines of Almadén the vein of sand is pure, without silver... Persons polishing cinnabar in workshops tie on their faces loose masks of bladder skin to prevent their inhaling the dust... which is very pernicious. Cinnabar is also used in writing books, and it makes a brighter lettering for inscriptions on a wall, or on marble, even in tombs... Hydragirium or artificial quicksilver is made in two ways, by pounding red lead in vinegar with a copper pestle in a copper mortar, or it is put in an iron shell... in pans... covered with a... lid... and then a fire is lit under the pans.” Abu-MusaDschafa-al-Sofi, or Geber (699 to 756), one of the most famous alchemists, assumed that quicksilver was the metallic essence of all metals, sulfur being the other component. Hence all metals were composed of varying proportions of sulfur and quicksilver. The sulfur content, being combustible, explained the change a metal experimented when heated, while the quicksilver content bestowed the metallic qualities, such as malleability and sheen. Although he did not recognize mercury as a metal, he regarded it as a substance of great consequence and is credited with having been the first to prepare red precipitate and to sublime mercuric dichloride in the course of his many experiments with it. He speaks of it as softening gold and was no doubt familiar with its properties of forming amalgams.8 Abu Bakr Muhammad bin Zakaria al-Razi, called Rahzes (850-923), Johanis Mesue (925-1015), and Ibn Sina or Avicenna (980-1037), used quicksilver, mercurial ointment, and mercury dichloride in treating itch and various other skin diseases; they also mentioned that the dichloride was poisonous. In due time, the use of quicksilver in medicine was definitely established by the Arabic physicians early in the Middle Ages of European history. Rahzes gave a fairly clear account of the synthesis of cinnabar. Part of his work, translated into Latin in the thirteenth century as Raziz de Aluminibus et Salibus, contains the following paragraph: “There is another method, and it is the coagulation of mercury with the odour (vapor) of sulphur. That is, you put it in a piece of thick cloth, tie it, and suspend it in a vessel. Place sulphur in the bottom of the vessel and seal up the junction. Kindle a fire under it for the whole day, and then take it off the fire so that it may cool. There you will find a red salt uzifur (from the Arabic, zanjufur = cinnabar)”. 6 The ancient Egyptians knew and used tin and copper amalgams. Some mercury flasks have been found in tombs dating back to 1 500 or 1 600 BCE. From the sixth century BCE their literature makes increasing mention of mercury, its preparations and uses. The Leiden Papyrus, although it dates from the third century CE, contains compilations of much older materials, and includes some prescriptions that contain mercury.6 The ancient Chinese and Hindus also knew mercury. Its production seems to have started in China at about the same time as in the Mediterranean world, and apparently independently. Mercury and cinnabar are mentioned in the Classical Pharmacopoeia (Shen Nung Pem Tshao Ozing). Some time later in the first millennium CE Chinese alchemists prepared both corrosive sublimate and calomel by heating various mixtures containing mercury, salt, and alum, and made a clear distinction between them. The preparation of both chlorides is described in the Great Pharmacopoeia (Pên Tshao Kang Mu) compiled in 1596. A mercury still is known dating from the later Han dynasty (first or second century CE). The earliest mirrors also date from this dynasty; they consist of a polished layer of tin amalgam on a bronze plate.6 The Chinese alchemist Ko Hung (281361 CE) wrote in the Pao Yu Tzu, “Many do not even know that mercury comes out of cinnabar (tan sha). When told, they still refuse to believe it, saying that cinnabar is red, and how can it produce a white substance? They also say that cinnabar is a stone; that stones when heated turn to ashes: and how then can anything else be expected of tan sha?” The mausoleum of Emperor Ch’i-Huang-Ti, who died in 210 BCE, contained a relief map of China in which the ocean was represented by a pool of quicksilver, and the Yangtze and the Yellow Rivers by flowing streams of quicksilver.8 As early as 500 BCE, India was using mercury as a drug. From there, its medical use was transmitted to Persia and perhaps to China. Up to about 1 000 CE mercurial drugs and alchemy as part of the gold making were not yet popular in Arthasastra. The use of mercury both in alchemy and medicine is found in India only in the later literature (earliest Tantric cult).10 The Arabs, after conquering the Iberian Peninsula, exploited the mines of Almadén and exported mercury and cinnabar. They used mercury as a decorative material, the most prominent example being the pool of mercury that was installed in the tenth century in the royal gardens at Medina Azahara (near the Alhambra). Revista CENIC Ciencias Químicas, Vol. 39, No. 3, 2008. 149 The Italian deposits of Monte Amiata in Toscana were discovered early and were worked first by the Etruscans, then by the Greeks and still later by the Romans. More detailed descriptions of the treatment of cinnabar and production of mercury began appearing around the sixteenth century in the first comprehensive metallurgical treatises, which were then being published. Those written by Vanoccio Biringuccio (14801538) and Georgius Agricola (1494-1555) are the best known. Biringuccio in his Pyrotechnia11 wrote: “Since semi minerals are not produced by Nature as all rocks or all metal; they are called so by speculative physicians. Many kinds of these are found, those that resemble rocks are earthy, very difficult to liquefy, and much more adapted for adorning paintings than for anything else. Those that liquefy with fire, like sulphur, antimony... and others resemble the metals almost like brothers. Some others are more watery so that they dissolve in water...These are the salts, vitriol rock alum, and saltpeter. To these, as a watery thing, belongs also quicksilver, as it is commonly called because of its motion. Although it appears not only as a liquid, but very liquid, this is not all similar in its effects to any of the above... Quicksilver is a body that consists of flowing and liquid materials, almost like water with a shining whiteness; it is composed by Nature of a viscous, subtle substance with an overflowing abundance of moistness and coldness together. This composition in the opinion of the philosophic alchemists, is a thing that is very disposed to become metal, indeed they say that it is the original seed of all metals. When it lacks the warmness and dryness or the specific time that they require, it cannot congeal and so remains in the form that we see as an imperfect thing without becoming a metal...These clever investigators have also called it mercury in consideration of its properties, perhaps because of its resemblance to the planet of him whose actions place him between gods and men, according to the poets in their stories. Alchemists in the opinion cited above wish to prove at all costs that quicksilver is truly a defect of Nature so that they can hope to remedy it with their art... Among its other notable qualities it also has this, that it holds suspended as a light thing any metal that is placed on top of it in a vessel, and bearing it up, allows it to float. An exception is gold, which it embraces and instead of holding it in suspension, it draws it into itself to the very bottom... It is used for many things in medicine on account of its coldness. It is numbered among the poisons. It has the property of contracting the nerves of those workers which extract it from ore, if they are not very careful, and it makes the limbs of those who continually handle it weak and paralysed. Mixed with silver and then distilled it makes cinnabar, and likewise mixed with sal ammoniac it makes what is commonly called corrosive sublimate or hard silver”. In book IX of his treatise, Agricola12 wrote that the knowledge of mercury seems to have first appeared in Greek sources. Mercury was found in pools in mines and was cleansed with vinegar and salt and refined by being squeezed through the pores of canvas or soft leather. He described five different methods extracting mercury from its ore. One of them consisted in heating the raw material in single and double pots, another used a domed chamber in which green trees were added to dry wood to accelerate the condensation of the mercury, and a third involved an iron tripod and giant earthenware pots. Agricola realised that mercury vapors are heavier than air and for that reason they could therefore conveniently be trapped in condensers beneath the reaction vessels. He also warned that if the fumes had a sweet odour it indicated that mercury was evaporating and that the workers had to move to the windward in order to avoid inhaling the fumes, which were dangerous and would cause loosening of the teeth. In 1640 Alvaro Alonso Barba (1569? -1661), a Spanish priest in the mining area of Perú, wrote El Arte de los Metales13 mainly about the extraction of gold and silver. This book was important and kept secret in Spain, until the British Ambassador, Edward Montagu, Earl of Sandwich (1625-1672), managed to get a copy and translated it in 1669. Barba, referring to mercury, wrote: “There was very little use or consumption of Quicksilver before the beginning of this new Silver age in the world, then they only wasted it in Mercury sublimate, Cinabrio, or Vermilion, and the powders made thereof called Precipitate, which are also called in Spain the powders of Juanes de Vigo, which have been used to such mischievous purposes that the world was said to have too much of them... it hath been used to collect the Silver together out of Oar, which is ground small... it is incredible how great a quantity is consumed by the Founders of Metals of this Kingdom: for if the abundance of Silver that hath gone out of this Kingdom bath filled the world with riches and admiration, by it may be estimated the consumption and loss of Quicksilver, which after a most extravagant expense thereof at first, being now by good experience regulated within terms of moderation, is found to be equal in weight to the Silver extracted; and very seldom that the waste is so little. . .“. The name vermilion was given to cinnabar, much valued on account of its brilliant scarlet color, and largely used as a pigment or in the manufacture of red sealing wax. Despite Barba’s belief that mercury entered into the composition of all metals, he denounced as ‘a great error’ the widely held opinion “that because for so many years the best Refiners in these Kingdoms have wasted at the least so much Quicksilver, as they have gotten Plate, therefore the Quicksilver is really and truly consumed in the operation” Instead of the messy patio process (see below) Barba recommended that amalgamation be carried out in closed vessels with stirring, and that laboratory tests of the silver ores be used to determine the best additives. The followers of Paracelsus (1493-1541) believed that all bodies were composed of the tria prima, salt, sulfur, and mercury, though these were not the substances ordinarily known by these names but symbols for qualities or principles. Robert Boyle (1627-1691) referred to the Paracelsian hypothesis in his book Sceptical Chymist,14 with these words: “And certainly he that takes notice of the wonderful operations of quicksilver, whether it be common, or drawn from mineral bodies, can scarce be so inconsiderate as to think it of the very same nature with that immature and fugitive substance which in vegetables and animals chymists have been pleased to call, their mercury.” Boyle, asserted that mercury was a “mixt body”, which nevertheless retained its identity through many chemical changes: “There are some mixt Bodies from which it has not been yet made appear, that any degree of Fire can separate either Salt or Sulphur or Mercury, much less all the three... How does this Hypothesis (of Paracelsus) shew us how much Salt, how much Sulphur and how much Mercury to make a Chick or a Pompion”. To the alchemist, mercury symbolised the expectation of converting the base metals into silver, or gold, or Revista CENIC Ciencias Químicas, Vol. 39, No. 3, 2008. 150 something even more valuable, which would possess its high density, mobility, sheen, freedom from tarnish, high surface tension, and the ease with which it wetted, dissolved, or amalgamated with other metals Alchemists designed as mercurius every volatile substance, thus alcohol was mercurius vegetabilis and mercury mercurius communis. Later on, the name mercurius was used only when referring to mercury.15 According to Nicolas Lemery16 (1645-1715), who used to mock the alchemists, all alchemists employed basically the same approach to gold making, which involved the extraction and manipulation of an essential or spiritual part of gold, which they called (philosophical) mercury or the seed of gold. The alchemists attempted to extract this essence from the purest part of lesser metals through the action of fire or a spiritual liquor. Those who considered this essence to be a seed of gold claimed that it could grow a mass of gold just like the seed of a vegetable grows a plant. Lemery appended to his critique of alchemical gold making an examination of the alchemists search for the universal medicine or potable gold. He began by lecturing on the proper uses of gold in medicine: as a cure for “frictious du mercure”, mercury poisoning. Since gold and mercury amalgamate easily, Lemery believed that one should ingest bits of gold to fix and interrupt the motion of mercury corpuscles that disrupted the normal functioning of the body. In scientific work mercury began to acquire especial importance after suitable glass apparatus was developed. In 1643, Evangelista Torricelli (1608-1647) showed that mercury in a sealed, inverted tube always sank to a level of about 76 cm . Afterwards, Blaise Pascal (1623-1662), Boyle, and others showed that the level was lower on a mountaintop. By 1662, Boyle showed that the mercury level was dependent on the outside air pressure, and thus that the weight of the column was equal to the weight of a similar column of air extending to the top of the earth’s atmosphere. The first closed-glass liquid thermometers, made around 1654, consisted of a glass tube closed at one end and having a liquid reservoir of large dimensions filled with distilled colored wine as the thermometric fluid. The advantage of a liquid like wine was that its expansion was independent of air pressure. Mercury and water thermometers were also tried by the Florentines but abandoned because their expansion was too small. Later this problem was overcome by the simple artifact of making thermometers with finer bores, thereby increasing their sensitivity. By the middle of the 18th century mercury thermometers had superseded others because of their more uniform expansion. An important advantage of mercury was that unlike other thermometric fluids, it was available in a high state of purity. The isolation of air and oxygen over mercury by Carl Wilhelm Scheele (1742-1786), Antoine-Laurent Lavoisier (1743-1794), and Joseph Priestley, (1733-1804) played an important part in elucidating the nature of air. Priestley initiated another important scientific use of quicksilver when he first used it to seal off water-soluble gases in making gas analyses.8