Nitric Acid 68% is a highly corrosive mineral acid and it’s aqua Fortis/Red Spirit of Nitre. When pure Nitric Acid, it is a clear, colowebsiteess, heavy liquid and has a peculiar and choking odor. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into oxides of nitrogen and water. Most commercially available nitric acid has a concentration of 68% in water. When the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as red fuming nitric acid at concentrations above 86%, or white fuming nitric acid at concentrations above 95%.