Calxes

A calx is a type of metal oxide formed by heating a metal or metal compound in the presence of air or oxygen. This process, known as calcination, involves the decomposition of a substance by heating it to a high temperature. The term "calx" is derived from the Latin word for limestone, as limestone (calcium carbonate) was historically one of the most common substances subjected to calcination to produce lime (calcium oxide).

Calxes are typically powdery or brittle solids. The specific properties of a calx depend on the metal or compound from which it is derived. For example, iron calx (iron oxide) has different properties than copper calx (copper oxide). The formation of calxes is a significant process in metallurgy, where it is used to extract metals from their ores. It is also employed in the production of various industrial chemicals and materials.

Historically, the term "calx" was also used more broadly in alchemy to refer to any powdery residue obtained by heating or burning a substance, often with the intention of purification or transformation. This alchemical usage predates the more precise chemical definition and often carried connotations of a purified or essential substance. Modern chemistry uses the term "oxide" for most calxes, though "calx" can still be encountered in historical contexts or in specific industrial applications.