Nitrobenzene is a chemical liquid that is often used as a solvent for chemical reactions. A dry sample of most liquid organic solvents can be prepared by using a drying agent. A drying agent is an inorganic solid salt that has a lot of surface area that will absorb any trace amounts of water from the nitrobenzene. But the drying agent itself won't dissolve in the nitrobenzene. The two most common drying agents are magnesium sulfate (MgSO4) and sodium sulfate (Na2SO4). The drying agent is added to the sample of nitrobenzene and allowed to sit for awhile to absorb any water present. Then the drying agent is removed by pouring the mixture through a filter. The dry sample of nitrobenzene is the filtrate and can be stored in a sealed bottle.