Mercury, an element in the periodic table, is the only metal that is liquid at room temperature. Mercury is highly toxic in both liquid and gaseous forms. Mercury readily forms alloys (collectively called amalgams) with a variety of metals, including gold and silver.
Mercury is used in thermometers, especially ones which are used to measure high temperatures. It is a toxic heavy metal, causing brain and liver damage if ingested. For this reason, thermometers which are only intended to measure typical climatic temperatures now use pigmented alcohol inststead.