This Huff and Puff Apparatus is used in school biology labs to demonstrate that carbon dioxide is a product of respiration.A pupil breathes in and out of the middle tube. The glass tubing is arranged in such a way that one flask bubbles as the pupils breathes in, the other as the pupil breathes out. A suitable carbon dioxide indicator, such as lime water or bicarbonate indicator shows the increased presence of carbon dioxide in the outgoing breath.
See Also: Respiration, How-to's, School Biology experiments and demonstrations, School chemistry experiments and demonstrations