POLYBASIC AND HYDROXY-ACIDS. 511 



Fatty acids. Hydroxy-acids. 



Formic acid, H.CO 2 H. Hydroxy-formic acid, OH.CO 2 H. 



Acetic acid, CH 3 .CO 2 .H. Hydroxy-acetic acid, CH 2 .OH.CO 2 H. 



Propionic acid, C 2 PI 6 .CO 2 H. Hydroxy-propionic acid, C 2 H 4 .OH.CO.,H. 



etc. etc. 



The first member of these hydroxy-acids designated as hydroxy-formic acid 

 is simply carbonic acid and does not partake of the general character of 

 hydroxy-acids. 



Monohydroxy-monobasic acids. 



Gly colic acid, CH 2 .OH.CO 2 H (Hydroxy-acetic acid), is found in 

 unripe grapes and in the leaves of the wild grape. It can be obtained 

 synthetically, as shown in the previous paragraph. It may also be 

 made by the oxidation of ethylene alcohol or ylycol, C 2 H 4 (OH) 2 thus : 



C 2 H 4 (OH) 2 -f 2O = CH 2 .OH.CO 2 H + H 2 O. 



Glycolic acid is a white deliquescent, crystalline substance, easily 

 soluble in water, alcohol, and ether. 



Lactic acid, Acidum lacticum, C 2 H 4 .OH.CO 2 H = 89.37 (Hy- 

 droxy-propionic acid), occurs in many plant-juices; it is formed from 

 sugar by a peculiar fermentation known as " lactic fermentation," 

 which causes the presence of this acid in sour milk and in many sour, 

 fermented substances, as in ensilage, sauer-kraut, etc. The formation 

 of lactic acid from sugar may be expressed by the equation : 



C 6 H 12 6 = 2(HC 3 H 5 3 ). 



Sugar. Lactic acid. 



For practical purposes lactic acid is made by mixing a solution of 

 sugar with milk, putrid cheese, and chalk, and digesting this mixture 

 for several weeks at a temperature of about 30 C. (86 F.). The 

 bacteria in the cheese act as a ferment, and the chalk neutralizes the 

 acid generated during the fermentation. The calcium lactate thus 

 obtained is purified by crystallization and decomposed by oxalic acid, 

 which forms insoluble calcium oxalate. 



Lactic acid is a colorless, syrupy liquid, of strongly acid properties ; 

 it mixes in all proportions with water and alcohol. The official 

 lactic acid contains 75 per cent, of absolute acid. 



Three isomeric lactic acids are known : 



a. Fermentation lactic acid, obtained as described above from milk, is opti- 

 cally inactive. 



b. Sarcolactic or paralactic acid is dextrorotatory and occurs in muscle and 

 other parts of the body. It forms a constituent of meat-juice, and, therefore, 

 of meat extract. 



c. Lcevolactic acid is laevorotatory, and is obtained from cane sugar by fer- 

 mentation by a special micro-organism. 



