36 



CHEMISTRY OF FARM PRACTICE 



tallized form of carbon. Most of anthracite, bituminous 

 coal, and charcoal is carbon. Graphite is almost pure 

 carbon. 



The three compounds of carbon that interest us most 

 from an agricultural view-point are carbon dioxide, the 

 carbonates, and the carbohydrates. The soil water con- 

 tains a certain amount of carbon dioxide, which is produced 

 through the decay of organic matter in the earth. The 

 higher the per cent of carbon dioxide in the water, the 

 greater will be its solvent power. Thus, water percolating 



? EPIDERMIS LOWER EPIDERMIS CROSS SECTION 



FIG. 8. Structure of a leaf. The stomata are shown in the lower 

 epidermis and in the cross-section. 



through the soil and absorbing carbon dioxide will dissolve 

 mineral matter and become hard water. 



The carbonates are compounds of carbon dioxide and 

 a basic anhydride. Thus, CaO+CO2 = CaCOs. Carbon- 

 ate of lime, CaCOs, is agriculturally the most important of 

 the carbonates. The carbohydrates contain carbon and 

 hydrogen and oxygen, the latter two being in the pro- 

 portion of water, H^O. The carbohydrates are formed 

 in plants by the condensation of formic aldehyde. Formic 

 aldehyde is formed in the green part of plants in the presence 

 of sunlight, by the union of carbon dioxide, which enters 

 through the stomata or breathing pores of the leaf of the 



