Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Nitrosyl chloride is the chemical compound NOCl. It is a yellow gas that is most commonly encountered as a decomposition product of aqua regia, a mixture of hydrochloric acid and nitric acid. The related nitrosyl halides nitrosyl fluoride, NOF, and nitrosyl bromide, NOBr, are also known. Although its formula is written NOCl, the structure is better represented ONCl. A double bond exists between N and O (distance = 1.16 Å) and a single bond between N and Cl (distance = 1.69 Å). The O-N-Cl angle is 113°. It also arises from the combination of hydrochloric and nitric acids according to the following reaction: HNO3 + 3 HCl Cl2 + 2 H2O + NOCl. Although this mixture was used for dissolving gold for a long time the first description of the gas was done by Edmund Davy in 1831