134 THE CARBOHYDRATES 



Again, oil is a convenient form of reserve food, especially 

 in small organisms and in reproductive bodies, where space is 

 limited and lightness is all-important and it is desirable to 

 store a maximum of potential energy in the minimum of bulk. 

 Finally, as Parkin points out, the nature of the carbohydrate 

 reserve may depend on the kind of sugar transformed ; thus, 

 if saccharose be the chief sugar translocated from the leaves, 

 then it might be expected that starch would be produced, on 

 the other hand inulin might be formed if the available sugar 

 for conversion were levulose. 



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 ; 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 sulphide, fil- 

 tered, neutralized with ammonia, evaporated to half its 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 little 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 



* Kiliani: "Annalen," 1880, 205, 147. 



