THE VOLATILE PAET OF PLANTS. 79 



Yery frequently occurs within the plant as microscopic 

 crystals. These are found in large quantity in the ma- 

 ture leaves and roots of the beet, in the root of garden 

 rhubarb, and especially in many lichens. 



Secondary ammonium oxalate is employed as a test for 

 calcium. 



EXP. 36. Dissolve 5 grams of oxalic acid in 50 c. c. of hot water, add. 

 solution of ammonia or solid carbonate of ammonium until the odor of 

 the latter slightly prevails, and allow the liquid to cool slowly. Long, 

 needle-like crystals of ammonium oxalate separate on cooling, the 

 compound being sparingly soluble in cold water. Preserve for future 



use. 



EXP. 37. Add to any solution of lime, as lime-water (see note, p. 20), 

 or hard well-water, a few drops of solution of ammonium oxalate. 

 Secondary Calcium oxalate immediately appears as a white, powdery 

 precipitate, which, from its extreme insolubility, serves to indicate the 

 presence of the minutest quantities of lime. Add a few drops of hydro- 

 chloric or nitric acid to the calcium oxalate; it disappears. Hence 

 ammonium oxalate is a test for lime only in solutions containing no free 

 mineral acid. (Acetic and oxalic acids, however, have little effect upon 

 the test.) 



Malonic acid and Succinic acid occur in plants in 

 but small quantities. The former has been found in 

 sugar-beets, the latter in lettuce and unripe grapes. 



Malic acid, C 4 H 6 5 , is the chief sour principle of ap- 

 ples, currants, gooseberries, plums, cherries, strawberries, 

 and most common fruits. It exists in small quantity in a 

 multitude of plants. It is found abundantly in the gar- 

 den rhubarb, and primary potassium malate may be ob- 

 tained in crystals by simply evaporating the juice of the 

 leaf-stalks of this plant. It is likewise abundant as cal- 

 cium salt in the nearly ripe berries of the mountain ash, 

 and in barberries. Calcium malate also occurs in con- 

 siderable quantity in the leaves of tobacco, and is often 

 encountered in the manufacture of maple sugar, separat- 

 ing as a white or gray sandy powder during the evapora- 

 tion of the sap. 



Pure malic acid is only seen in the chemical laboratory, 

 and presents white, crystalline masses of an intensely 

 sour taste. It is extremely soluble in water. 



