DETERMINATION OF MALIC ACID. 



11 



to the desired concentration. The sugar solutions always contained 

 more or less sodium chlorid resulting from the neutralization of the 

 acid used for inversion. New malic acid stock solutions were made 

 up every two or three days, as a growth of mold usually appears after 

 a few days' standing. In many cases Reading (3) was not made. 

 Wherever possible it is given, however. It will be noted that in 

 many cases Reading (3) is higher than (2) for the reason previously 

 explained. When the former is lower, the percentage of malic acid 

 is calculated from it. The most favorable concentrations of malic 

 acid appear to be between 0.2 and 2.5 per cent. Below 0.2 per cent 

 the increase in polarization due to the uranium-malic complex is so 

 small that a small error in reading may make a relatively large error 

 in the final result, while above 2.5 per cent the increase in specific ro- 

 tation tends to give high recoveries. 



The results shown in Table VI illustrate the applicability of the 

 method to natural products. The strawberry juice used as a solvent 

 was highly colored and most of the readings had to be made in 50 

 or 100 mm polariscope tubes. 

 TABLE V. Determinations on solutions containing known amounts of malic acid. 



i Determinations by C. W. Clark. 



