58 



FRUITS AND FRUIT PRODUCTS. ' 



TABLE 20 Continued. 



POLARIZATION OF COMMERCIAL JELLIES CONTAINING NO GLUCOSE. 



POLARIZATION OF JELLIES CONTAINING GLUCOSE. 



Sample 20185 is especially to the point. It has an invert reading 

 of 8.80 and no dextrin was found by fermentation, but the differ- 

 ence of +12.90 indicates the presence of a dextrorotatory sugar, in all 

 probability dextrose. It is in such cases that the method of compari- 

 son shows the great value of polarization after inversion for the detec- 

 tion of a small amount of added dextrose which may not contain enough 

 dextrin to be detected by the fermentation process. 



The polarization after fermentation witn yeast, by which all the 

 sugars are removed, is approximately zero and does not vary more 

 than 0.3 in the case of products which contain no glucose, but 

 in the glucose products the right-handed polarization of the dextrin 

 is unchanged. Great care must be used, however, to secure com- 

 plete fermentation or very erroneous results will be obtained. Dex- 

 trose is more easily fermented than levulose, so that a zero reading 

 could be obtained even though a considerable amount of dextrin were 

 present, the left-handed reading of the levulose neutralizing the right- 



