ORGANIC COMPOUNDS OF PLANTS 205 



under uniform conditions, the results are comparable and 

 are of value when properly interpreted. 



Organic Acids 



C 273. Occurrence in Plants. In all plants and vege- 

 table foods, there are present bodies known as organic 

 acids. An organic acid, like all acids, contains hydrogen 

 which can be replaced by a metal (see Section 75).) The 

 negative radical of the acid contains carbon, hydrogen, 

 and oxygen. For example, in tartaric acid, H 2 C 4 H 4 O 6 , 

 the H 2 can be replaced by a metal ; C 4 H 4 O 6 is the tartaric 

 acid radical. Organic acids, like mineral acids, are 

 neutralized by bases. 



Tartaric Potassium 



acid. tartrate. 



2KOH + H 2 C 4 H 4 6 = K 2 C 4 H 4 O 6 + 2H 2 O. 



As a rule, the organic acids are not present in a free 

 state, but are combined with base-forming elements, as 

 potassium and calcium, forming organic and acid salts. 

 In plants, the organic acids are found mainly in solution, 

 as in the sap. When the plant matures, they are used 

 either for the construction of other organic compounds, 

 or are neutralized by bases to form insoluble salts, as 

 calcium oxalate, and deposited as crystals in the leaves. 

 A small amount of acid is found in all mature seeds, and 

 during germination, some of the carbohydrates are con- 

 verted into acids. In green vegetables and small fruits, 

 the organic acids are found more liberally than in the 

 seeds of grains ; in the leaves and stems of matured 

 plants, but little acid is found. Some of the organic 

 acids from fruits are of commercial value, as crude tar- 



