PP.INCIPLES OF VENTILATION. 



255 



above stated. It has been calculated that hot-houses, during the 

 application of fire heat, contain four times as much carbonic 

 acid in their atmosphere as is necessary for the health of the 

 plants. 



" Charcoal possesses the property of absorbing some gases to a 

 great extent, as may be seen by the following table, in which 

 the numbers indicate the volumes of gases absorbed, that of the 

 charcoal being taken as unity ."^ 



Absorption of Gases by Charcoal. 



Ammonia, 90 



Muriatic acid, 85 



Sulphureous acid, 65 



Sulphuretted hydrogen, . ... 55 



Nitrous oxide, 40 



Carbonic acid, 35 



Bi-carb. hydrogen, 35 



Carbonic oxide, 9.4 



Oxygen, 9.2 



Nitrogen, 7.5 



Carbur. hydrogen, 5 



Hydrogen, 1.7" 



The above table will show how very useful charcoal may be 

 rendered as an agent in the absorption of these gases, when 

 present in excess, either in a plant-house or other places. 



3. The evolution of heat by plants is most evident at those 

 periods of their existence in which an extraordinary quantity of 

 carbonic acid is formed and given off. This is the case during 

 the germination of seeds ; and though the heat produced by a 

 single seed is too soon carried off by surrounding bodies to be 

 perceptible, it accumulates to a high degree, Avhere a number 

 are brought together, as in the process of malting, when the 

 thermometer has been seen to rise 110°. An extraordinary 

 amount of carbonic acid has been found to accumulate in a hot- 

 house, in one night, so as sensibly to affect the respiration of in- 

 dividuals entering the house in the morning ; which shows the 

 necessity of night ventilation. The disengagement of carbonic 

 acid has been sensibly found in some plants, by the evolution 

 of heat in some of their organs. Thus, the flower of a gera- 

 nium has been found to possess a heat of 87°, when the air 

 around it was 81°. As in the case of seeds, however, the pro- 

 duction of heat is most sensible where the flowers are crowded 

 together, and in those flowers where the size of the fleshy disk ia 



22# * Daniel's Introduction to Chemistry. 



