[301] SCIENTIFIC MANUAL. 15 



gradually undergoes a change, and becomes a brownish, 

 black substance, loose and friable in its texture, resem- 

 bling coal." In some countries and cities peat is of value, 

 and is used as fuel. For this purpose it is cut out in square 

 blocks, dried in the sun and pressed. It contains about 

 60 per cent of carbon. 



Muck is a variety of peat, containing more impurities 

 and less fully carbonized. The largest bed of this material 

 in Georgia is in Okefenokee Swamp, in the lower part of the 

 State. It has there a thickness of several feet, and ex- 

 tends over many square miles. 



Its value as a fertilizer is due mainly to its power of ab- 

 sorbing and retaining moisture and the ammonia of the at- 

 mosphere, and to the amount of mineral plant-food it may 

 contain. 



Humus is a general name applied to the partially decom- 

 posed vegetable matter embracing that contained in peat and 

 muck, and as well as that resulting from the decay of green 

 crops turned under. Its value, as well as the rapidity of the 

 decomposition, depends upon the kind of vegetable matter 

 from which it is formed. Its beneficial effects upon soils 

 are due principally to its mechanical action in stiffening 

 sandy and loosening clay soils ; in its absorbtive and re- 

 tentive power for moisture and ammonia ; in its solvent 

 power in rendering available mineral substances in the soil ; 

 and in supplying small amounts of plant-food liberated 

 by the process of decomposition. The principal element 

 evolved from humus is carbonic acid. 



Catbonic Acid is a gas composed of carbon and oxygen, 

 in the proportion of one atom of carbon to two of oxygen, 

 and like other acids, is generally combined with other sub- 

 stances to form solids. For example, in chalk and marble 

 we have this gas combined with lime. It, however, is also 

 free in nature. It exists free in the atmosphere, and often 

 in caves, mines, and old wells. It is colorless, has a pun- 

 gent odor, and pleasant acid taste. It is heavier than the 



