174 THE CARBOHYDRATES 



never contain inulin, but do contain dextro-rotatory sugars 

 and starch. The formation of inuhn begins in the stem and 

 is completed in the tubers. Thus the inuhn must be formed 

 from dextro-rotatory sugars synthesized in the leaves. 



Preparation. 



Inulin may be obtained from dahlia tubers, of which it 

 forms from 10-12 per cent, by crushing them and pressing out 

 the liquid and filtering ; the residue is then boiled up with a 

 little water and some precipitated chalk and filtered again. 

 The two filtrates are then united and once more boiled with 

 chalk in order to neutralize any acids, and while still warm 

 treated with lead acetate until no further precipitate is formed. 

 The filtered solution is then saturated with hydrogen sul- 

 phide, filtered, neutralized with ammonia, evaporated to small 

 bulk, and mixed with an equal volume of alcohol. After one 

 or two days, crude inulin may be filtered off ; it may be further 

 purified by warming in aqueous solution with animal charcoal, 

 filtering, and adding alcohol ; the precipitated inulin is then 

 washed with alcohol and ether, and dried over sulphuric acid. 



According to Kiliani,* it may also be prepared by boiling 

 crushed dahlia tubers with water and a Httle chalk, filtering 

 and freezing the filtrate. When the water cools, the precipi- 

 tate is filtered off, re-dissolved in hot water and frozen out 

 once more. After repeating this process several times, the 

 inulin is washed with methyl alcohol, ethyl alcohol, and finally 

 ether. 



Characters. 



Pure inulin forms a white starchy tasteless powder of a 

 sphaero-crystalline nature ; it swells up and is readily dissolved 

 in hot water, alkalis, etc., and may be recovered from the 

 aqueous solution by the addition of alcohol, in which it is 

 practically insoluble, or by freezing. Highly purified inulin 

 should give less than 0-2 per cent of ash, but the removal of 

 the last traces of inorganic substances is so difficult as to 

 suggest that they form a definite part of the molecular com- 



* Kiliani : " Annalen," 18S0, 205, 147. 



