200 VEGETABLE ACIDS. 



plants in the free state, but are combined with 

 various bases derived from the soil ; sometimes they 

 are found in the state of perfectly neutral salts, but 

 more frequently they form acid salts (111); that is to 

 say, there is more acid than the base is able to neu- 

 tralize ; such plants have a sour taste. 



494. When the salts of organic acids are burned 

 or strongly heated, the acids are decomposed ; in 

 these cases, the base, which was previously combined 

 with the organic acid, is found, after its destruction, 

 combined with carbonic acid, in the state of a car- 

 bonate (546). 



495. The most important of the organic acids, are 

 the acetic, citric, tartaric, malic, and oxalic. There 

 are few plants which do not contain a small portion 

 of one or other of these acids, either in the free 

 state, or else combined with a base. Unripe fruit 

 contains a considerable quantity of malic and tar- 

 taric acids ; and the leaves and stems of many plants, 

 such as sorrel and rhubarb, have a strong, sour taste, 

 from the presence of oxalic and malic acids. The 

 nature and properties of acetic acid have already 

 been described (476). 



496. Citric acid exists in a free state, abundantly 

 in the juice of limes and lemons, and in unripe goose- 

 berries, currants, and other similar fruits ; it is easily 

 procured from these sources, in white crystals, having 

 an agreeable, sour taste, and readily dissolving in 

 water. Citric acid is used in considerable quantity 

 by dyers : none of its salts are of much importance. 



