Natural History (Pliny) developed for counterfeit coins and proved very popular with the victims, mostly ordinary people. He deals with the liquid metal mercury, also found in silver mines. He records that it is toxic, and amalgamates with gold, so is used for refining and extracting that metal. He says mercury is used for gilding copper, while antimony is found in silver mines and is used as an eyebrow cosmetic. The main ore of mercury is cinnabar, long used as a pigment by painters. He says that the colour is similar to "scolecium", probably the kermes insect. The dust is very toxic, so
Ore extension which means that "δ" is a homomorphism of abelian groups satisfying Then the Ore extension "R"["x";"σ","δ"], also called a skew polynomial ring, is the noncommutative ring obtained by giving the ring of polynomials "R"["x"] a new multiplication, subject to the identity If "δ" = 0 (i.e., is the zero map) then the Ore extension is denoted "R"["x"; "σ"]. If "σ" = 1 (i.e., the identity map) then the Ore extension is denoted "R"["x","δ"] and is called a differential polynomial ring. The Weyl algebras are Ore extensions, with "R" any commutative polynomial ring, "σ" the identity ring endomorphism, and "δ" the