56 AMERICAN AGRICULTURE. 



CHAPTER III. 



ORGANIC MANURES. 



THE PRINCIPLES CONSTITUTING- ANIMAL AND VEGETABLE 

 PUTRESCENT OR ORGANIC MANURES. 



FROM the table in the foregoing pages on the ashes of 

 plants, it is shown, that in burning dried vegetables, they 

 lose from about 95 to 99 per cent, of their whole weight. 

 The matter that has been expelled by heat, consists of four 

 substances or ultimate principles ; carbon, oxygen, hydrogen 

 and nitrogen, of which carbon makes up from 40 to 50 per 

 cent., or about one half of the whole. 



Carbon constitutes all of charcoal but the ash; nearly 

 all of mineral coal, and plumbago or black lead ; and even 

 the brilliant diamond is but another form of carbon. The 

 properties and uses of carbon are various and important ; 

 its agency in the growth of plants alone, concerns us at the 

 present time. 



Carbonic Acid. When any matter containing carbon is 

 burned, its ultimate particles or atoms combine with the 

 oxygen which exists in the atmosphere, and form carbonic 

 acid, consisting by weight, of six of the former and sixteen 

 of the latter. When animals inhale air into their lungs, a 

 similar union takes place ; the carbon contained in the sys- 

 tem being brought to the surface of the lungs, and after 

 uniting with the oxygen, is expelled as carbonic acid. Pure 

 limestone or marble loses 46 per cent, of its weight by 

 burning ; and all of this loss is carbonic acid, which the 

 lime slowly absorbs again on exposure to the air, or to such 

 substances as contain it. It is evolved by fermentation ; and 

 if the surface of a brewer's vat in full activity, be closely 

 observed in a clear light, it may be seen falling over the 

 edges, when it is gradually absorbed by the air. Its density 

 is such, that it may be poured from one open vessel into 

 another, without material loss. It is this which gives to 



