Nitrobenzene preparation under reflux. This is a stage in the nitration of benzene. The pear- shaped flask contains a solution of nitrobenzene. It is being boiled in a flask attached to a reflux condenser (upper centre). The reflux condenser has cold water flowing around it, provided by pipes (orange). This rapidly cools any vapour that rises from the solution, causing it to condense and fall back into the flask.