104 SCIENCE PRIMERS. [xxvi. 



have collected at the top of the bottle. These 

 bubbles consist of pure oxygen gas derived from the 

 carbonic acid contained dissolved in the spring water. 

 This shows that plants have the power in presence 

 of sunlight of decomposing carbonic acid, taking 

 the carbon to build up their stems, leaves, &c., and 

 setting free the oxygen as a gas. Now repeat the 

 experiment ; but instead of placing the bottle of spring 

 water containing the leaves in the light, put it in a 

 dark cellar. There will then be no formation of 

 bubbles of oxygen gas, even after standing for many 

 hours. This shows that sunlight is necessary in order 

 that green plants may decompose carbonic acid, and 

 is therefore necessary for their growth. 



158. Respiration. In the green parts of plants 

 the giving off of carbonic acid gas, which takes place 

 in the respiration of all living things, is 'not observed 

 owing to the action of chlorophyll in decomposing 

 carbonic acid. It becomes, however, very evident in 

 parts which are not green. 



Fill one-third of a wide-mouthed stoppered bottle of 

 rather less than two quarts capacity with soaked peas, 

 or with the expanding flower heads of camomile or 

 daisy. If the bottle is carefully opened after several 

 hours the air contained will be found to extinguish a 

 burning taper. This is due to the presence of carbonic 

 acid gas. 



By taking special precautions and using a very 

 delicate thermometer, it is possible to show that a 

 distinct rise of temperature takes place during the 

 evolution of the carbonic acid. An illustration on a 

 large scale of this rise of temperature is afforded by 

 malt during its manufacture. 



