FERMENTS AND MISCELLANEOUS PRODUCTS 97 



C 2 H 4 (COOH) 2 , is of fairly common occurrence, especially in 

 the composite and papaveraceae. It is found in grapes and 

 other fruits, and is one of the products in many different types 

 of fermentation, e.g. alcoholic fermentation of sugars. 



(4) Hydroxydibasic Acids. Tartronic acid and malic acid 

 are perhaps the commonest members of this group. The 

 former is hydroxymalonic acid, CH(OH):(COOH) 2 , and the 

 latter hydroxysuccinic acid, CH 2 .CH(OH).(COOH) 2 . Malic 

 acid is the characteristic acid of apples, strawberries, and 

 many other fruits and vegetable products From the present 

 standpoint it is chiefly of interest on account of its rela- 

 tion to asparagine and aspartic acid (p. 52). Tartaric acid, 

 (CHOH) 2 (COOH) 2 , is dihydroxysuccinic acid. It also occurs 

 in many fruits. The potassium hydrogen tartrate called argol 

 separates out from the juice of grapes during the process of 

 fermentation. When purified, this salt is known as cream of 

 tartar. 



(5) Citric Acid. The characteristic acid of oranges and 

 lemons is a hydroxytribasic compound corresponding to the 

 formula C 3 H 4 (OH)(COOH) 3 . 



