58 CARBOHYDRATES AND THEIR [ch. 



Weigli out another 25 gms. of barley grains and allow tliem to germinate by 

 soaking and spreading on damp blotting-paper for 5-7 days. Found the grains well 

 in a mortar, add 100 c.c. of water, allow to stand for 2-3 hrs. and filter. Precipitate 

 the filtrate with alcohol and allow to stand for 24 hrs. Filter off the precipitate, 

 take up in water and add it to the barley starch " solution," together with a few 

 drops of chloroform. Proceed as with (a) only the time for hydrolysis may be much 

 shorter, i.e. 6-12 hrs. 



Expt. 58. Tests for dextrin. Make a solution of the dextrin prepared in the last 

 experiment and note that it is very soluble in water. With the solution make the 

 following tests : 



(a) Add a little iodine solution. A reddish-brown colour is produced. Heat the 

 solution and the colour will disappear. Cool again and the colour will reapjjcar. 



(6) Add an equal volume of strong alcohol. The dextrin is precipitated. 



(c) Add an equal volume of saturated ammonium suli)hate solution, i.e. half 

 saturation with ammonium sulphate. The dextrin is not precipitated. 



{d) Add some basic lead acetate solution: the dextrin is not precipitated. 



Inulin. 



Inulin. This substance occurs as a soluble "reserve material" in the 

 cell-sap of the underground stems, roots and also leaves of a number of 

 plants, especially members of the Compositae, e.g. Dahlia {Dahlia 

 variabilis), Jerusalem Artichoke {Helianthus tuberosus), Chicory (Cicho- 

 rium Intybus) and the Dandelion {Taraxacum ojfficinale). It is said to 

 occur also in the Campanulaceae, Lobeliaceae, Goodeniaceae, Violaceae 

 and many Monocotyledons {Hyacinthus, Iris, Muscari and Scilla). 



Inulin is a condensation product of laevulose to which it bears much 

 the same relation as starch to glucose. It is a white substance, soluble 

 in water and insoluble in alcohol. It crystallizes out in the cells, in 

 which it occurs, in characteristic sphaero-crystals on addition of alcohol 

 to the tissues. It is hydrolyzed by mineral acids to laevulose : also by 

 the enzyme inulase which occurs in the plant. 



E.cpt. 59. Extraction of iaidin. Cut off the tubers from two Dahlia {Dahlia 

 variabilis) plants, wash well, and put them through a mincing machine. Carefully 

 collect the liquid and the crushed tuber, and boil well with sufficient water to cover 

 the crushed material. Add also some precipitated calcium carbonate to neutralize 

 any free acids present. Then filter through fine muslin, and to the filtrate, which 

 should again be made quite hot, add lead acetate solution until a precipitate 

 (of mucilaginous substances, etc.) ceases to be formed. Care should be taken to 

 avoid the addition of a large excess of lead acetate. Filter off the lead precipitate, 

 and saturate the filtrate with sulphuretted hydrogen till all excess lead is removed. 

 Filter oft" the lead sulphide, neutralize the filtrate to phenolphthalein with ammonia, 

 and evaporate to half bulk or less on a water-bath, when the inulin will probably 



