DETERMINATION OF SUGARS AND DEXTRINS 153 



proteids and removing all traces of lead from the filtrate with a 

 current of H 2 S, the filtrate should be treated with gelatine to re- 

 move tannins by the method already given, and the solution fil- 

 tered clear and the filtrate preserved. A little chloroform 

 should be added as an antiseptic if the solution is not to be 

 examined immediately. 



A minute examination of the filtrate would probably reveal 

 several different carbohydrates. For the present purpose it will 

 be sufficient to examine it for glucoses, maltose, cane-sugar, 

 dextrins and inulin. 



The direct and accurate determination of the quantities of differ- 

 ent sugars and dextrins in the same solution is hardly possible by 

 any of the methods now known. It is obvious that the polariscope 

 cannot be depended upon entirely to identify any particular sub- 

 stance when there are several optically active in the same solution. 

 Most of the precipitants usually employed do not exercise sufficient 

 selectivity, and carbohydrates of different classes are carried down 

 together. Fermentation processes are hardly more satisfactory, 

 inasmuch as yeast not only decomposes glucoses, but inverts and 

 subsequently breaks down the disaccharids as well. It will be 

 possible, however, to outline some qualitative determinations which 

 will enable one to identify those sugars and dextrins most com- 

 monly occurring in plants. 



The aqueous solution should be divided into several parts. 

 One part is evaporated to a syrup and about ten volumes of 

 99 per-cent. alcohol added. After stirring well the precipitate 

 is collected on a filter, washed thoroughly with alcohol of the 

 grade noted above and dried. This precipitate may be considered 

 mostly dextrin, though it is probable that some reducing sugar 

 may be present also. The weight of the dry precipitate may be 

 taken and some idea gained of its proportion to the other sub- 

 stances. The precipitate should then be dissolved in water and a 

 part of this solution tested with iodine. A red coloration will in- 

 dicate erythrodextrin, blue will indicate amylodextrin. The 

 color should disappear on heating and reappear on cooling. 



