" Formerly OpenVista. Hg stands for hydrargyrum (/haɪˈdrɑrdʒɨrəm/), is the modern chemical symbol for what we know as mercury. Hydrargyrum come from a Latinized form of the Greek word Ύδραργυρος (hydrargyros), which is a compound word meaning "water" and "silver"; since it is liquid, like water, and yet has a silvery metallic sheen. Hg has atomic number 80 and has seven stable isotopes with Hg-200 being the standard atomic weight. Of the metals, only Hg is liquid at standard conditions for temperature and pressure with the melting point of -38.83°C and the boiling point of 356.73°C. Hg is an extremely rare element in the Earth's crust, having by mass of only 0.08 ppm. Hg is harmless in an insoluble form, but Hg poisoning can result from exposure to soluble forms. Acute exposure to Hg vapor has been shown to result in profound central nervous system effects, including psychotic reactions characterized by delirium, hallucinations, and suicidal tendency. "