To show that oxygen is used in respiration.
Soaked germinating maize seeds in water for about a day, until they are fully swollen and place them in a conical flask together with a test-tube containing caustic soda. The caustic soda will absorb any carbon dioxide which will be released as a result of respiration of the grains. A delivery tube is connected through the cork of the conical flask and its other end dips into a beaker of water. A control experiment is set up without maize grains.
It is found after some time, that the water in the beaker rises in the delivery tube, indicating that some gas has been removed from the air in the flask containing the maize grains.
If a glowing taper is put into the flask it does not burst into flame, showing that nearly all the oxygen has been used up. On the other hand, a glowing taper continues to glow in the control flask without maize grains, where no water rise is observable. Therefore, oxygen is used up by respiring seedlings, and for that matter by respiring plant tissues.