Nitric acid is a product of ammonia and is a key chemical inside the manufacture of fertilizers. The natural compound is colorless, however older samples tend to gather a yellow cast. By far the primary use of nitric acid (80%) is within the manufacture of fertilizers. Of this 96% is used to make ammonium nitrate and calcium ammonium nitrate. A noticeably small quantity of ammonium nitrate is used to make explosives.