of elements that have not yet been prepared. It has adopted a procedure by which the scientists who are credited with preparing an element can propose a new name. Once the IUPAC has accepted such a (trivial) name, it replaces the systematic name. Origins Nine elements were known by the Middle Ages: gold, silver, tin, mercury, copper, lead, iron, sulfur, and carbon. Mercury was named after the planet, but its symbol was derived from the Latin hydrargyrum, which itself comes from the greek υδράργυρος, meaning liquid silver; mercury is also known as quicksilver in English. The symbols for the other eight are derived from their Latin names. Systematic nomenclature began after Louis-Bernard Guyton de Morveau stated the need for “a constant method of denomination, which helps the intelligence and relieves the memory”. The resulting system was popularized by Antoine Lavoisier's publication of Méthode de nomenclature chimique (Method of Chemical Nomenclature) in 1787. Lavoisier proposed that elements be named after their properties. For the next 125 years, most chemists followed this suggestion, using Greek and Latin roots to compose the names; for example, hydrogen ("water-producing"), oxygen ("acid-producing"), nitrogen ("soda-producing"), bromine ("stink"), and argon were based on Greek roots, while the names of iodine and chlorine were derived from the Greek words for their characteristic colors. Indium, rubidium, and thallium were similarly named for the colors of particular lines in their emission spectra. Iridium, which forms compounds of many different colors, takes its name from iris, the Latin for "rainbow". The noble gases have all been named for their origin or properties. Helium comes from the Greek helios, meaning "Sun" because it was first detected as a line in the spectrum of the Sun (it is not known why the suffix -ium, which is used for metals, was chosen). The other noble gases are neon ("new"), argon ("slow, lazy"), krypton ("hidden"), xenon ("stranger"), and radon ("from radium"). Many more elements have been given names that have little or nothing to do with their properties. Elements have been named for celestial bodies (helium, selenium, tellurium, for the Sun, Moon, and Earth; cerium and palladium for Ceres and Pallas, two asteroids). They have been named for mythological figures, including Titans in general (titanium) and Prometheus in particular (promethium); Roman and Greek gods (uranium, neptunium, and plutonium) and their descendants (tantalum for Tantalus, a son of Zeus, and niobium for Niobe, a daughter of Tantalus);