Equipment used in an experiment to oxidise an alcohol (ethanol) with potassium dichromate, an oxidising agent. At top, the burette contains orange potassium dichromate, an oxidising agent. The tap releases this to flow into the flask at bottom, containing ethanol, an alcohol. As the reaction proceeds, the change of colour from orange to green indicates that the chromate ions have been reduced, and thus that the oxidation of the alcohol, to ethanal, has taken place.