Nitric Acid (HNO3) also known as aqua fortis and spirit of niter, is an oily, yellowish liquid, which is a strong acid and good oxidising agent. Its main use is in getting nitrogen (originally from the air) into compounds. Nitric acid is made naturally by rain water reacting with nitrogen oxides in the air. These oxides are made when the high temperatures in lightning force nitrogen and oxygen to react together.

By far the principal use of nitric acid (80%) is in the manufacture of fertilizers. Of this 96% is used to make ammonium nitrate and calcium ammonium nitrate. A relatively small amount of ammonium nitrate is used to make explosives.
Some nitric acid is used to make intermediates in the polymer industry, notably in the manufacture of hexanedioic acid (adipic acid) to make polyamides and TDI (toluene diisocyanate or methylbenzene diisocyanate) and dinitrobenzene two of a range of reagents used to make polyurethanes. Nitrobenzene is used to make aniline which is a key reagent for making dyes.