136 BIOLOGY OF PLANTS. 



In fact it is wood partially decayed. It is insoluble in water, 

 but is converted by the agency of water, air or alkalies, into 



2. Humic acid, which is identical in composition with it. Hu- 

 mic acid is a brownish-black substance, floculent when first pre- 

 cipitated, and soluble in 2,500 times its weight of water, and 

 becomes less and less soluble the longer it is exposed to the 

 air. It is composed, according to Sprengel, of carbon 58. , hy- 

 drogen 2.10, and oxygen 39.90 in 100 parts. Boullay gives the 

 composition of g-e?c acii/, which is identical with humic acid. 

 Malagutti gives nearly the same composition. 



Boullay. Malagiitti 



Oxygen 55.70 or 15 atoms 



Hydrogen 4.81 15 



Carbon 38.49 30 



Oxygen 57.48 



Hydrogen 3.76 



Carbon 37.36 



yy.60 



Hence its composition may be represented by C^^VL^^O^^==oy 

 about 58 per cent, of humic acid is carbon. 



3. Crenic acid, from krene the Greek word for fountain, is 

 composed, according to the analysis of Hermann, of C^'H^^NO^. 

 When pure it is of a yellow color, quite transparent, with no 

 tendency to crystallize. It has no odor, but its taste is sharp, at 

 first acid, and afterwards astringent. When in solution the 

 astringent taste alone can be perceived. It is excessively soluble 

 in loater and alcohol. It combines with lime, and forms the cre- 

 naie of lime, which is soluble in water, and the subcrenate of 

 lime which is insoluble. The crenates of potassa, ammonia and 

 soda, resemble extracts of a yellowish color, very soluble in 

 water, and in weak alcohol. 



The crenate of magnesia is readily dissolved in water, but the 

 neutral crenate of alumina is insoluble, while the subsalt is solu- 

 ble. The crenate of iron is also soluble in water. Hence, as all 

 these substances are found in the soil, and nearly all are solu- 

 ble in water, they nuist enter the organs of plants with that fluid. 



4. Jijjocrenic acid is formed from the crenic, by simply ex- 

 posing the latter to the air. Its composition niay be represent- 

 ed thus: C^^H^'^N^O^. It is a brown extract, possessing a 

 purely astringent taste. It is slightly soluble in water, is readilj'^ 

 dissolved in crenic acid, and slowly in alcohol. As the crenic 

 acid always, upon exposure, changes into this acid, the existence 

 of the former appears essential to the i)roduction of the latter. 



The ffy?ocrena/e.s of potassa, ammonia and soda arc black, fria- 

 ble masses, and when soluble in water, are of a dark-brown 



