What is fuming nitric acid?

Fuming nitric acid is a pale-yellow to reddish-brown liquid that generates red-brown fumes. It is toxic to inhale, corrosive to metals and tissue, and both prolonged exposure to low concentrations or short exposure to high concentrations can result in adverse health effects.

Fuming nitric acid is a strong oxidizing and nitrating agent. It accelerates the burning of combustible materials, causing charring and ignition of the materials. It may ignite several compounds that include alcohols, ammonia, amines, boranes, hydrocarbons and powdered metals. It fumes in air and is soluble in all proportions in water. When dissolved in water, heat, fumes and spattering occur.