OXYPROPIONIC ACIDS. 147 



2. Oxypropionic Adds. 



Both of the acids, possible according to the theory, 

 are known. 



1. Lactic acid (Ethylidenelactic acid) = CH 3 . 



{OTT 

 CO OH ^ s P r duced by ^ e souring of milk by 



fermentation of the sugar of milk contained in it. 

 In the same way it is formed from cane-sugar, grape- 

 sugar, gum, starch, when these are left for some time 

 in contact with water and old cheese or similar protein 

 substances at a temperature of 20-50 (lactic fermenta- 

 tion). It is hence contained in large quantity in acidi- 

 fied vegetable juices (for instance, in beet juice, in 

 saurkraut), and its presence has also been proven in 

 animal liquids, particularly in the gastric juice. It is 



E reduced from a -chlor- or a-brompropioriic acid, and 

 rom alanin in the same manner as the homologous 

 glycolic acid is prepared from chloracetic acid and 

 glycocol; further, by the action of hydrochloric acid 

 on aldehyde hydrocyanate (see p. 104), and of nascent 

 hydrogen on pyroracemic acid. 



Most practically prepared in the following manner : 

 3 kilogrammes cane-sugar and 15 gr. tartaric acid are 

 dissolved in 17 litres boiling water and allowed to 

 stand several days ; 100 grms. old cheese, suspended in 

 4000 grms. sour milk, and 1200 grms. zinc white are 

 then added, and the temperature retained as nearly as 

 possible at 40-45 during the period of fermentation. 

 In eight to ten days the fermentation is ended. 

 The whole mass is now heated to boiling, filtered, 

 evaporated, and allowed to crystallize. The separated* 

 zinc lactate is crystallized again from hot water, then 



* The fermentation is prevented by any large amount of free acid, 

 and hence ceases as soon as this is formed, long before all the sugar is 

 decomposed. This can, however, be avoided by neutralizing the acid, 

 from time to time, by means of a base, or by adding a base at the com- 

 mencement. 



