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 ORGANIC ELEMENTS OF SOIL. 7S 



and humln, geic, apocrenic, and crenic acids are formed in 

 the order in which they have been named. Each is derived 

 from the substance immediately preceding it in the Jist. 



The ultimate product of their decay is carbonic acid and 

 water*. 



The acids of geine easily and rapidly absorb ammonia 

 and water. They also chemically combine with water and 

 ammonia. 



They are seldom found free in soil, ana so energetic is 

 the affinity between crenic and apocrenic acid and ammonia, 

 that these have been considered as essentially different from 

 ulmic, humic and geic acids. These contain carbon, hydro- 

 gen and oxygen, while crenic and apocrenic acid were sup- 

 posed to contain in addition, nitrogen. Hence, a distinction 

 was pointed out in the last edition of this work, in which 

 geine was divided into nitrogenous and non-nitrogenous* 



The progress of discovery has shown that crenic and apo- 

 crenic acid may be derived from geic acid, free from nitrogen. 



102. Still there are wide differences in the relations of 

 these several substances. The most easily marked charac- 

 teristic is, that some are easily, others difficultly soluble in 

 water, and others are insoluble in this element. 



The relations of the acids and neutral substances of geine 

 to alkalies, is also remarkable. All the geine acids readily 

 dissolve in carbonated or caustic alkali ; in either of which 

 the neutral geine substances are wholly insoluble. 



Of the dissolved acids, thfee are precipitable and two not 

 precipitable by acids. Hence, we have two divisions of 

 geine founded on their relations to alkali and water; 1st, 

 {soluble, and 2d, insoluble. The insoluble substances are 

 ulmin and humin. The soluble substances are all acid, and 

 these may be still further distinguished by their relations to 

 acid. 



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