78 HOW CROPS GROW. 



Dibasic Acids> "^The acids of this class requiring notice 



are 



COOH 



OOH 



Malonic acid, C S H 4 O<, or CH 2 



Oxalic add, C.H,O 4 , or 



C 



Succinic acid, CJ^O^, or 



C 



CHj COOH 



H. COOH 

 CH 2 COOH 



Malic acid (Oxysuccinic acid), C 4 H 6 O 5 , or 



CH(OH)-COOH 

 CH(OH) COOH 



Tartaric acid (Dioxysuccinic CiHgOg, or 



acid), CH(OH) COOH 



The salts formed by union of these acids with metallic 

 bases are either primary or secondary, according as the 

 metal enters into one or two of the carboxyls. 



Oxalic acid, C 2 H 2 4 , exists largely in the common 

 sorrel, and is found in greater or less 

 quantity in nearly all plants. The pure 

 acid presents itself in the form of color- 

 less, brilliant, transparent crystals, not 

 unlike Epsom salts in appearance (Fig. Fig. 15. 

 15), but having an intensely sour taste. 



Primary potassium oxalate (formerly termed acid ox- 

 alate of potash), HOOC COOK, occasions the sour taste 

 of the juice of sorrel, from which it may be obtained 

 in crystals by evaporating off the water. It may also be 

 prepared by dissolving oxalic acid in water, dividing the 

 solution into two equal parts, neutralizing * one of these 

 by adding solution of potash and then mixing the two 

 solutions and evaporating until crystals form. 



Secondary potassium oxalate (neutral oxalate of potash), 

 KOOC COOK, is the result of fully neutralizing oxalic 

 acid with potash solution. It has no sour taste. 



Primary calcium oxalate exists dissolved in the cells 

 of plants so long as they are in active growth. Second- 

 ary calcium oxalate is extremely insoluble in water, and 



* As described in Exp. 38. 



