Mercury is the densest liquid at standard conditions for temperature and pressure (STP). Also called quicksilver, mercury has been known for more than 3,500 years. It is an important metal in industry, but it is also toxic.

Mercury measures 13.534 grams per cubic centimeter. That’s thirteen and a half times more dense than water, which scientists have assigned a density of 1.0.

Density is the measurement of an object’s mass divided by its volume. Density cannot be measured directly; instead, a scientist takes a weight measurement of an object and then calculates its volume. The volume can be calculated by measuring the amount of water displaced in a container, such as a graduated cylinder, when the object is submerged. Finally, the scientist divides the mass (in grams) by the volume (in cubic centimeters) to obtain the density.

The only metallic element that is liquid at room temperature, mercury is a very shiny silver metal and is element number 80 on the periodic table. Its symbol is Hg, which stands for its Latin name Hydrargyrum, which means “liquid silver.” Mercury has 34 isotopes, 6 of which are stable.

Mercury conducts electricity and is used in a variety of devices, such as:

• thermometers
  
• barometers
  
• batteries
  
• reed switches

The gas form of the element is used in mercury-vapor lamps, and mercury is also used in the production of pesticides and other chemicals.

Mercury is toxic and should be avoided. During the early nineteenth century, hat makers used mercury in their products. Breathing the fumes eventually caused kidney and brain damage and led to the phrase “mad as a hatter.” The term is still used to describe mercury poisoning.