20 PRACTICAL FARM CHEMISTRY. 



an acid taste and smell, and considerably heavier 

 than common air. 



Now, while thousands of stoves and furnaces and 

 lamps are pumping carbonic acid into the air with- 

 out cessation; while a stream of the same gas issues 

 from every pair of lungs (the process of life is only 

 a combustion of carbonaceous matter); while decay- 

 ing vegetable and animal substances also give forth 

 quantities of the gas; the atmosphere, which 

 naturally contains one part of it in each 2,500 parts 

 of the oxygen-nitrogen mixture called air, would 

 soon become overcharged with it, and unfit to sus- 

 tain animal and even plant life, if no provision were 

 made by nature for just this emergency. But plants 

 and trees must have carbon, and are hungry for it. 

 So they set their traps all over the 



^Carbonic Acid?^ ^^^^ *^ catch this substance as it 

 is floating in the air. The leaves 

 and even the stems of plants are full of pores, and 

 through these the carbonic acid gas is absorbed and 

 brought into circulation in the sap, where it under- 

 goes chemical changes, and is manufactured into 

 starch, sugar, plant fibre, etc., all of which sub- 

 stances are largely or chiefly composed of carbon. 

 The carbon is retained, while the oxygen is again 

 exhaled; and the right proportion between the gases 

 — the proper balance in the atmosphere — is thus 

 maintained. 



While plants and trees thus obtain a large portion 

 of their carbon from the vast and unceasingly re- 

 newed stores in the atmosphere, the roots also 

 absorb more or less of it from the soil. Carbon, in 

 its simple or elementary form, is insoluable in water, 

 and oxygen is only soluble to a very small extent. 

 Their compound, "carbonic acid," however, dis- 



