50 AMERICAN AGRICULTURE. 



CHAPTER III. 



ORGANIC MAN U RES. 



THE PRINCIPLES CONSTITUTING ANIMAL AND VEGE- 

 TABLE PUTRESCENT OR ORGANIC MANURES. 



From the table in the foregoing pages on the ashes of 

 plants, to which reference has been frequently made, it is 

 shown that in burning dried vegetables, they lose from 

 about 93 to 99 per cent, of their whole weight. The mat- 

 ter that has been expelled by heat, consists of four substan- 

 ces 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 

 burnt, its minute particles or atoms combine with the 

 oxygen which exists in the atmosphere, and form carbonic 

 acid, consisting by weight of 6 of the former and 16 of the 

 latter. When animals inhale air into their lungs a similar 

 union takes place ; the carbon contained in the system being 

 brought to the surface of the lungs, and after uniting with 

 the oxygen as carbonic acid, is expelled. Pure lime- 

 stone or marble loses 46 per cent, of its weight by burning; 

 and all of this loss is carbonic acid, which it slowly absorbs 

 again on exposure to the air, or to such substances as con- 

 tain 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 gradu- 

 ally mingles with the air. Its density is such that it may be 



