ORGANIC MAITEKS OF THR SOIL. 223 



Verdeil and Risler hare made similar observations on ten 

 soils from the farm of tlie Institut Agronomiqne^ at Ver- 

 sailles. Thoy found that the water-extract of these soils 

 contained, on tlie average, 50" j^, of organic matter, which, 

 wlien strongly heated, gave an odor like burning paper or 

 sugar. These observers make no mention of crenatcs or 

 apocrenates, and it, perhaps, remains somewhat doubtful, 

 therefore, wliether their researches really demonstrate the 

 presence in tlie soil of a neutral body identical with, or 

 allied to, dextrin or sugar. 



Cellulose, starch, and dextrin, pass by fermentation into 

 sugar (glucose) ; this may be resolved into lactic acid (the 

 acid of sour milk and sour-krout), butyric acid (one of the 

 acids of rancid butter), and acetic acid (the acid of vine- 

 gar). It must often happen that the bodies of the cellu- 

 lose group ferment in the soil, the same as in the souring 

 of milk or of dough, though they suffer for the most part 

 conversion into humus, as will be shortly noticed. 



Vegetable Acids, viz., oxalic, malic, tartaric, and citric 

 acids, become ingredients of the soil when vegetable mat- 

 ters are buried in it. When the leaves of beets, tobacco, 

 and other large-leaved plants fall upon the soil, oxalic and 

 malic acids may pass into it in considerable quantity. 

 J'alling fruits may give it citric, m.alic, and tartaric acids. 

 These acids, however, speedily suffer chemical change 

 when in contact with decaying albuminoids. Buchner has 

 shown {Ann. Ch. u. Ph., 78, 207) that the solutions of 

 salts of the above-named vegetable acids are rapidly con- 

 verted into carbonates Avhen mixed with vegetable ler- 

 ments. In this j^rocess tartaric and citric acids ai'e first 

 partially converted into acetic acid, and this subsequently 

 jjasses into carbonic acid. 



Volatile OrJ^anic Acids. — Formic, propionic, acetic, and 

 butyric acids, or rather tlieir salts, have been detected by 

 Jongbloed and others in garden earth. They are comjuoa 



