The density of mercury far exceeds that of ordinary liquids, so even an iron block placed on the surface of mercury can float

Mercury is the common name for quicksilver, and it is also the only metal element that is liquid at room temperature and standard pressure. The so-called density of mercury refers to the mass contained in a unit volume of mercury, with a value of about 13.6 grams per cubic centimeter, which is more than thirteen times that of the same volume of water, making it the heaviest among common liquids.

The reason the density of mercury is so high is closely related to the relatively large mass of the mercury atom itself. It is also precisely for this reason that many metals, such as iron blocks and zinc blocks, can float when placed on the surface of mercury, a phenomenon often used to demonstrate the relationship between buoyancy and density. Historically, mercury was also used, by virtue of its own properties, in measuring instruments such as barometers, thermometers and blood pressure monitors.

It should be noted that density is not unchanging. Mercury expands when heated, and its density then decreases slightly, and old-fashioned mercury thermometers use precisely this principle to indicate temperature. For everyday reference and general calculations, taking the approximate value at room temperature is usually good enough.

Although mercury has a high density, its vapor is toxic, so both use and storage require care. Once a thermometer or blood pressure monitor is broken, first open the windows for ventilation, then use a piece of stiff paper to collect the scattered mercury beads into a sealed bottle and hand it over to a specialized agency for disposal. Never pour it into the drain or discard it at will. Friends engaged in agricultural production should also pay attention to mercury-containing materials when dealing with scenarios such as soil testing and old agricultural supplies, so as to avoid causing pollution.