[MUSIC] Alchemy is, in its most literal sense, an attempt at transmuting vile metals as lead or copper into noble metals, silver or gold. Indeed, gold is not only the most valuable metal, it is also the only metal known to medieval alchemists which does not corrode. In this way, alchemists tried to make corruptible metals unalterable. However, alchemy does not only consist of argyropeia and chrysopeia, (namely making silver and gold), but covers a wider field of study. Already in Antiquity, alchemy could be defined as a discipline in which one finds technical practices mingled with philosophical doctrines of the time. Contrary to what is commonly believed, most parts of alchemical treatises include technical recipes, which are not fanciful fantasies, but often show empirical knowledge. The alchemists were not only trying to make gold, but were also dyeing metals, refining salts, and many other processes. The word 'alchemy' derives (through Latin) from the Arabic al-kīmiyā’, which is itself most probably taken from the Greek χυμεία or χημεία (meaning fusion, alloy), or, but this is less probable, from the Egyptian <i>qmyt</i>, which means 'resin' or 'gum'. The history of the word 'alchemy' reflects the history of alchemy itself. Alchemy was born during the Antiquity. The first textual evidences date back to Hellenistic Greece, although its origin might be Ancient Egypt; then it passed to the Arabic World. According to the legend, the first Arabic Alchemist was Khālid ibn Yazīd, the fourth Umayyad caliph, who lived in the seventh Century. He would have received the teachings from a Greek monk named Maryānūs . However, the historical truth of this event cannot be demonstrated, and if alchemy may well have reached the Arabic world very soon, it is above all through the translations from Greek or Syriac (on the occasion of the wide movement of translation of the eighth and ninth centuries) that the East discovered this science. The Arabic world inherited Greek alchemy and assimilated it very rapidly. Very soon, one finds not only translations from the Greek, but also genuine Arabic writings. Those were at first often attributed to famous Greek figures such as Pythagoras, Socrates or Plato, but names of Arabic alchemists appeared as early as in the second half of the eight century. Arabic alchemists made new technical discoveries, such as hydrochloric acid, for instance, but they also developed the philosophical trend of alchemy. On the basis of their metallurgical and chemical experiments, alchemists explained physical and chemical processes through the philosophical systems of their time, and sometimes through their own systems; and they applied their explanations not only to their metallurgy but to the whole world. Alchemy became a 'total science'. The most famous and prominent Arabic alchemist was Jābir ibn Ḥayyān (in the second half of the 8th century). A very large collection of alchemical texts was attributed to this figure (we do not know whether this is part of the legend, or of history), and this collection is usually referred to as the corpus Jābirianum. Although the core of this collection may have been written by a single person, maybe Jābir ibn Ḥayyān himself, many treatises were obviously written by other hands, between the second half of the 8th century and the 9th century, or even later. This corpus is one of the earliest witnesses of Arabic alchemy, but also, by far, the most influential. Indeed, it deeply influenced almost all later authors, up to one of the last great Arabic alchemists, Jildakī. The Jābirian texts, brought forward a physical doctrine inspired by the Greek system of the four elements as found in the words of Galen, but refined to an exceptional degree of complexity. Each thing of the sublunary world is compounded of four elements: fire, earth, air and water. These four elements are in turn characterized by four elementary properties: Fire is hot and dry, air is hot and moist, water is cold and moist, and earth is cold and dry. Things are distinguished from each other by their proportion of elements, and consequently by their proportion of elementary properties. The Jābirian authors innovated and developed a theory which had a prominent influence on the whole alchemical tradition, in the East and in the West, namely the elixir theory. Since a thing is characterized by its elements proportion, it is theoretically possible, when this proportion is modified, to transform a thing into another, for instance, lead into gold. How can this be done? We calculate the elementary proportions of lead and gold, and we evaluate the 'intensity' of the four properties in them. In this way, we know how much of each property we must add to lead to turn it into gold. Then, we take a material called 'stone' (ḥajar in Arabic), but which is not necessarily a stone: it could be a mineral, an animal, or a plant. We distil it in order to isolate its four elements. We work on these elements in order to reduce the 'intensity' of one of their two properties, and in order to obtain, by this way, pure heat, pure coldness, pure dryness and pure moisture. Then, we produce a mixture of these four properties according to the proportion which must be added to lead. This mixture is called 'elixir', (from the Arabic al-iksīr, itself from the Greek ξήριον, ‘dry powder'). We project the elixir on the lead to transmute it into gold. This system will become a standard for all alchemists. This is one of the main principles of Arabic alchemy. Another important figure of Arabic alchemy is Abū Bakr al-Rāzī, who lived at the turn of the 9th and 10th centuries. His alchemy may be characterized as more empirical than any other treatise of his time. Rāzī often relied on his own experiments more than on authorities, especially for his classification of materials, which remained for long one of the most precise and detailed classifications. Alchemy is often said to have flourished in the Islamicate world until the 14th century, the last important figure being Jildakī, but new investigations about Turkish alchemy show that this conception has to be revised, and that alchemy in the Arab-Muslim world was actually alive much longer than what was thought to this day. [MUSIC]