Mercury(I) sulfide
Mercury(I) sulfide or mercurous sulfide is a hypothetical chemical compound of mercury and sulfur, with chemical formula Hg2S. Its existence has been disputed; it may be stable below 0 °C or in suitable environments, but is unstable at room temperature, decomposing into metallic mercury and mercury(II) sulfide (mercuric sulfide, cinnabar). == History == This compound was described in the 19th century by Berzelius as a black precipitate obtained by passing hydrogen sulfide H2S through solutions of mercury(I) salts.