White fuming nitric acid, pure nitric acid or WFNA, is very close to anhydrous nitric acid. It is available as 99.9% nitric acid by assay. One specification for white fuming nitric acid is that it has a maximum of 2% water and a maximum of 0.5% dissolved . Anhydrous nitric acid has a density of 1.513 g/cm and has the approximate concentration of 24 molar. Anhydrous nitric acid is a colorless, low-viscosity (mobile) liquid with a density of 1.512 g/cm that solidifies at  to form white crystals. As it decomposes to  and water, it obtains a yellow tint. It boils at . It is usually stored in a glass shatterproof amber bottle with twice the volume of head space to allow for pressure build up, but even with those precautions the bottle must be vented monthly to release pressure.