72 ORGANIC ELEMENTS OF SOIL. 



These details may be tabulated, and thus the products of 

 putrefaction being seen at a glance, may be readily sealed on 

 the memory. 



PUTREFACTION PRODUCES IN 

 Free air, Oonfined air, 



Water, Water, 



Carbonic acid, Carbonic oxide, 



Ammonia. Carburetted hydrogen. 



Sulphuretted hydrogen, 



Phosphuretted hydrogen, 



Ammonia, 



Geine. 



In soil, the air being partly free, partly confined, all the 

 above products may be found. These vary, therefore, 

 according as the putrefying body may be on the soil, in the 

 soil, or in the subsoil. 



101. There are at least seven well-defined substances in- 

 cluded in the class geine. Two of these are indifferent in their 

 relations, viz. : ulmin and humin ; five exhibit acid proper- 

 ties, these are the ulmic, humic, geic, crenic, and apocrenic 

 acids. These seven substances are compounds of carbon, 

 with oxygen and hydrogen, in proportions just sufficient to 

 form water, or compounds having either the hydrogen or 

 the oxygen in excess. They may be therefore grouped in 

 three sections. 



1st. Carbon and water form humin and humic acid. 



2d. Carbon and water with hydrogen in excess, form 

 ulmin and ulmic acid. 



3d. Carbon and water with oxygen in excess, form geic, 

 crenic, and apocrenic acids. 



These may be termed the neutral, the hydrogen, and the 

 oxygen groups. 



The first products of decay are ulmin and ulmic acid. By 

 the continued absorption of oxygen from the air, humic acid 



