80 HOW CHOPS GROW. 



Tartaric acid, C 4 H 6 6 , is abundant in the grape, 

 from the juice of which, during fermentation, it is de- 

 posited as argol. This, on purification, 

 yields the cream of tartar (bitartrate of 

 potash) of commerce. Tartrates of po- 

 tassium and calcium exist in small quan- 

 tities in tamarinds, in the unripe berries 

 of the mountain ash, in the berries of the sumach, in cu- 

 cumbers, potatoes, pineapples, and many other fruits. 

 The acid itself may be obtained in large glassy crystals 

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



Of the Tribasic Acids known to occur in plants, but 

 one need be noticed here, viz., citric acid. 



C H 2 C O O H 



C 6 H 8 T ,or C(OH)COOH 

 C H a C O H 



Citric acid exists in the free state in the juice of the 

 lemon, and in unripe tomatoes. It accompanies malic 

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

 raspberry. It is found in small quantity in tobacco 

 leaves, in the tubers of the artichoke (Helianthus), in the 

 bulbs of onions, in beet-roots, in coffee-berries, in seeds of 

 lupin, vetch, the pea and bean, and in the needles of the 

 fir tree, mostly as potassium or calcium salt. It also 

 exists in cows' milk. 



In the pure state, citric acid forms large transparent or 

 white crystals, very sour to the taste. 



Relations of the Vegetable Acids to each other, and to the Amyloses.-* 

 Oxalic, malic, tartaric and citric acids usually occur together in our 

 ordinary fruits, and some of them undergo mutual conversion in the 

 living plant. 



According to Liebig, the unripe berries of the mountain ash contain 

 much tartaric acid, which, as the fruit ripens, is converted into malic 

 acid. Tartaric acid can be artificially transformed into malic acid, and 

 this into succinic acid. 



When citric, malic and tartaric acids are boiled with nitric acid, or 

 heated with caustic potash, they all yield oxalic acid. 



Cellulose, starch, dextrin, the sugars, yield oxalic acid when heated 



