THE VEGETABLE KINGDOM. 391 



By means of ingenious investigations, Professor Liebig 

 has even proved that the chemical nature of the atmosphere 

 has not varied sensibly for upwards of 2000 years. He 

 took one of the little glass vases in which, on the death of 

 persons who were dear to them, the Roman ladies collected 

 their tears, and which, after being partly filled, were her- 

 metically sealed by fusion, and deposited in the sarcophagus 

 with the dead. The lachrymal vase having been broken 

 and its contents analyzed, the great chemist found that the 

 air was of exactly the same composition as the fluid which 

 we respire nowadays. 



M. Lacreze-Fossat was enabled, by means of delicate ex- 

 periments, to determine the proportion of respirable gas 

 discharged into the atmosphere by certain plants. This ob- 

 server noticed that in twelve hours the under surface of the 

 large floating leaves which the yellow water-lily (Nymplicea 

 luted) spreads out on our rivers produced over ten cubic 

 inches of oxygen. And, according to him, a single speci- 

 men of this plant, composed of fifteen leaves, in five months 

 exhaled into the atmosphere 117.7 gallons. 



How much, then, must be produced in a single season by 

 a large tree, the respiratory surface of which is of such a 

 size compared to that of the aquatic plant ! 



It would require 10,000 years for all the people on earth to produce an effect on 

 the air appreciable by Volta's eudiometer (an instrument for measuring the purity 

 of the air), even supposing that vegetable life remained annihilated during all 

 that time. Thus the proportion of oxygen the air contains is guaranteed for 

 many ages, even entirely excluding the action of plants. Nevertheless, these 

 incessantly return to it as much oxygen as it loses, and perhaps more, for plants 

 also exist as much at the expense of the carbonic acid furnished by volcanoes as 

 at that of the acid expired by animals. Dumas, Essai de Statique Chimlque des 

 Etres Organises, Paris, 1842, p. 18. 



