DIBASIC AND TRIBASIC ACIDS. 331 



44. DIBASIC AND TRIBASIC ORGANIC ACIDS. 

 Dibasic acids of the general composition C n H 2a -2O 4 . 



Oxalic acid H 2 C 2 O 4 (CO 2 H) 2 . 



Malonicacid . . . . . H 2 C 3 H 2 O 4 or C H,(CO 2 H) 2 . 



Succinicacid H 2 C 4 H 4 O 4 or C. 2 H 4 (CO 2 H) 2 . 



Pyrotartaric acid .... H 2 C 5 H 6 O 4 or C 3 H 6 ( CO 2 H) 2 . 



Adipicacid H 2 C 6 H 8 4 orC 4 H 8 (C0 2 HV 



etc. 



Of these acids, only the first member is of general interest. 



Oxalic acid, H 2 C 2 O 4 .2H 2 O. This acid may be looked upon as a 

 direct combination of two carboxyl groups, CO 2 H CO 2 H, both 

 atoms of hydrogen being replaceable by metals. 



Oxalic acid is distributed largely in the vegetable kingdom in the 

 form of potassium, sodium, or calcium salts. It may be obtained 

 from vegetables, or by the oxidation of many organic substances, 

 chiefly fats, sugars, starch, etc., by nitric acid or other strong oxidiz- 

 ing agents. 



Experiment 74. Pour a mixture of 15 c.c. nitric acid and 35 c.c. of water 

 upon 10 grammes of sugar contained in a 200 c.c. flask. Apply heat gently 

 until the reaction begins. When red fumes cease to escape pour the solution 

 into a porcelain dish and evaporate to about one-half its volume. Crystals of 

 oxalic acid separate on cooling ; use them for making the analytical reactions 

 mentioned below. 



Oxalic acid is manufactured on the large scale by heating sawdust 

 with potassium or sodium hydroxide to about 250 C. (482 F.), 

 when the oxalate of these metals is formed ; by the addition of cal- 

 cium hydroxide to the dissolved alkali oxalate, insoluble calcium 

 oxalate is formed which is decomposed by sulphuric acid. 



Oxalic acid crystallizes in large, transparent, colorless prisms, con- 

 taining two molecules of water ; it is soluble in water and alcohol, 

 and has poisonous properties. When heated slowly, it sublimes at a 



processes may formic acid be obtained, and what are its properties? 427. 

 Describe the processes of manufacturing acetic acid from alcohol and from 

 wood. 428. What is vinegar, and what is glacial acetic acid ? Give tests for 

 acetic acid and for acetates. 429. Describe the processes for making the 

 acetates of potassium, zinc, iron, lead, and copper, and also of Goulard's ex- 

 tract and lead-water ; state their composition and properties. 430. When and 

 in what form of combination is oleic acid found in nature, and what are its 

 properties ? 



