Nitric acid acts as an acid in the manufacture of chemical fertilizers; it acts as a base in the manufacture of nitro compounds; it acts as an oxidizing agent in many systems. In making the fertilizer ammonium nitrate from nitric acid, it is necessary to neutralize the acidity of HNO3. This is accomplished by addition of NH3. In nitration reactions, such as the making of nitrobenzene, nitric acid is made to act as a base in the presence of sulfuric acid and forms nitronium ion which is the reactive intermediate in the nitration reaction. As an oxidizing agent, nitric acid can be reduced to a number of different products. The temperature of the system helps to determine which reaction predominates. The manufacture of nitric acid is a process which starts with the oxidation of ammonia, and includes several steps. Achieving a maximum yield of the acid illustrates the application of Le Chatelier's principle. Science Consultant: Professor Harry H. Sisler, University of Florida, Gainesville. Produced in cooperation with the Chemical Manufacturers Association.