FORMATION OF ACIDS AND ALCOHOL. 87 



latter is again dissipated by a drop of potash. The pres- 

 ence of iodoform is proved by the characteristic odor 

 and, microscopically, by the small six-sided iodoform 

 plates. For the differentiation of alcohol, aldehyd, and 

 acetone, consult Vortmann, Analyse organ. Stoffe, 1891. 



Then one acidifies strongly with phosphoric acid, and 

 with the aid of a current of steam distils off the volatile 

 acids. The distillation must be long continued, as the 

 complete separation of the volatile acids is difficult. The 

 non- volatile lactic acid (together with some succinic acid) 

 remains behind and is separated by repeated shaking with 

 pure ether, the ether then being distilled off. 



The lactic acid obtained is always ethylidenlactic acid, 

 CH3.CHOH.COOH, which occurs in two stereoisomer^ 

 forms : (1) dextrorotatory with levorotatory zinc salts ; 

 (2) levorotatory with dextrorotatory zinc salts. If, as is 

 frequently the case, almost equal molecules of levorotatory 

 and dextrorotatory lactic acid are present, then the mix- 

 ture is optically inactive and is the so-called "fermenta- 

 tion lactic acid. ' ' I believe that often both lactic acids 

 originate from sugar, but that many bacteria use up one 

 acid exclusively or principally, while others appropriate 

 the other acid. Thus may occur now a uniform mixture 

 of both acids, now one acid exclusively or preponderantly. 



Since Schardinger (Mitt. f. Chem. xi, 545) first discov- 

 ered the previously unknown levorotatory lactic acid as a 

 product of a short bacillus from water, many investiga- 

 tions have been made, especially by the pupils of Nencki 

 and Rubner, regarding the lactic acids formed by different 

 varieties of bacteria, with the hope of utilizing the results 

 in differential diagnosis. 



For the methods for determining which lactic acid is 

 present, consult Nencki (C. B. ix, 305) and Gosio (A. H. 

 xxi, 114). They have to do with the determination of 

 polarization and the water-content of the zinc salt. 



