As a part of a program aimed at the recovery of gases given off in the Darex process, a process involving the dissolution of stainless-steel-clad reactor fuel elements in aqua regia (<i>6,7</i>), a study was undertaken of the rate of evolution and chemical nature of the gases evolved under high reflux conditions from boiling aqua regia, both with and without metal present. The analytical technique employed infrared and visible spectrophotometry and gas chromatography; it afforded a quantitative measure of the stable gases N<sub>2</sub>O, NO, NO<sub>2</sub>, NOCl, Cl<sub>2</sub>, HCl, HNO<sub>3</sub>, N<sub>2</sub>, O<sub>2</sub>, H<sub>2</sub>, and H<sub>2</sub>O. Of these, HNO<sub>3</sub> and O<sub>2</sub> were never detected, and one compound existing in very small proportions was unidentified.
Clyde Orr and Margaret C. Kordecki, "Aqua Regia Off-Gases by Infrared Spectrophotometry," Appl. Spectrosc. 15, 180-181 (1961)