Organic synthesis. Apparatus used to manufacture nitrobenzene. The round-bottomed reaction flask is held in a beaker of cold water by a clamp. On top of the reaction flask is a dropping funnel. This contains benzene which is added slowly, dropwise, to the mixture in the flask. This is the nitrating mixture, which is concentrated sulphuric acid and concentrated nitric acid. The acids react and give out heat when mixed. The addition of the benzene to the nitrating mixture also produces heat, which is why the cold water and slow addition is needed. Nitrobenzene is used mainly to manufacture dyes, as well as other organic chemicals.