Arsenic is the element with an atomic number of 33. Its atomic weight is 74.9216, and its chemical symbol is As. It usually occurs as a silver-gray brittle solid, but it has at least two other allotropic forms. One is a black amorphous solid, and another a yellow, crystalline solid. When heated, arsenic sublimes rather than melts, although at pressures of about 28 atmospheres, it can be made to melt at 817° C. Free arsenic is produced by reducing arsenic (III), As₂O₃, oxide with charcoal.

Arsenic is one of the four elements to become well known through the work of alchemists in the Middle Ages. The element derived its name from the Greek word arsenikos, for "male." Some early scholars believed that metals, like animals, were either male or female. Two substances closely related to arsenic, orpiment and realgar, were generally regarded as "masculine." So when the new element arsenic...