88 HOW CROPS GROW. 



bicarb&aate of soda, Na H CO 2 . The latter is mu th less alkaline than 

 the former, but both turn cochineal to a carmine color. Again, phos 

 phoric acid may form three distinct salts with soda or with lime, which 

 will be noticed in another place. Oxalic acid also yields several kinds 

 of salts, us do the other organic acids presently to be described. 



Malic acid, C 4 H 6 O 6 , 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 combina 

 tion with potash, in the garden rhubarb, and malate of 

 potash may be obtained in crystals by simply evaporating 

 the juice of the leaf-stalks of this plant. It is likewise 

 abundant as lime-salt in the nearly ripe berries of the 

 mountain ash, and in barberries. Malate of lime also 

 occurs in considerable quantity in the leaves of tobacco, 

 and is often encountered in the manufacture of maple su 

 gar, separating as a white or gray sandy powder during 

 the evaporation 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. 



Tartaric acid, C 4 II, O 6 , is abundant in the grape, from 

 the juice of which, during fermentation, it is deposited in 

 combination with potash as argol. This, 

 on purification, yields the cream of tartar, 

 (bitartrate of potash, ) of commerce. Tar- 

 trates of potash or lime exist in small 

 quantities in tamarinds, in the unripe ber- Fig. 16. 



ries of the mountain ash, in the berries of the sumach, in 

 cucumbers, potatoes, pine-apples, and many other fruits. 

 The acid itself may be obtained in large glassy crystals, 

 (see Fig. 16,) which are very sour to the taste. 



Citric acid, C 6 H 8 O 7 , exists in the free state in the juicb 

 of the lemon, and in unripe tomatoes. It accompaniea 

 malic acid in the currant, gooseberry, cherry, strawberry, 

 and raspberry. ) It is found in small quantity, united to 



