AGRICULTURAL CHEMISTRY. SB 



contains about 44 lbs. in one hundred of carbonic 

 acid. When this is brought from the quirry and 

 burnt into quick-lime, the carbonic acid is driven into 

 the air. This is another source of re-supply. So 

 when coal is drawn from the mine, and burnt, its car- 

 bon, long shut up in the bowels of the earth, is again 

 set afloat for the use of plants. Many springs, as 

 those at Saratog^ are throwing small, but constant 

 streams of carbonic acid into the air. Volcanoes also, 

 so long as active, are throwing out large quantities of 

 it ; and fissures in the earth, particularly in volcanic 

 regions, often throw it out abundantly, and diffuse it 

 through the atmosphere. It is true that large amounts 

 of it are absorbed into the rivers, seas, and oceans, 

 where it goes to support marine vegetation, to form 

 the shells of fish, and to help build immense coral 

 reefs ; and some have feared that the atmosphere of 

 the globe would ere long become so exhausted of it, 

 as not to be able to sustain a vegetation equal to the 

 growing wants of the race. But, when we consider 

 the sources of re-supply above mentioned, we need 

 not be alarmed; though it must be confessed that 

 geology reveals a state of vegetation in by -gone pe- 

 riods, which proves that the atmosphere must have 

 been more highly charged with this food of plants 

 than at present. The fact that carbonic acid is a poi- 

 sonous gas, and that it is always passing from the 

 lungs of animals, shows the necessity of thorough 

 ventilation in our rooms ; and that our cattle even, 

 though to be kept comfortably warm, should not be 

 enclosed so tightly as to be compelled to breathe over 

 their own breath. 

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