66 CELL-CONTENTS AND CELL-WALLS. 



and it is precipitated, often in spherical crystalline masses, 

 on extraction of the water by alcohol or glycerine. 



(a) Examine commercial inulin. Place some of it in a test-tube, 

 add cold water, shake up, filter, and apply to the filtrate the tests 

 given below it is only slightly soluble. On being treated with hot 

 water, however, it dissolves readily. 



(6) To the cold-water solution add Fehling, and boil : no reduc- 

 tion occurs. To the solution made with boiling water add hot 

 Fehling, and boil for a few minutes : a little cuprous oxide is thrown 

 down, because the hot water converts some of the inulin into 

 glucose. To another portion of the hot-water solution add a little 

 sulphuric acid, boil, and test with Fehling : a copious precipitate 

 is given. 



(c) Allow some of the hot- water solution to cool, and set the test- 

 tube aside : the inulin is precipitated, but very slowly. To a little 

 of the cooled solution add excess of alcohol : the inulin is quickly 

 thrown down. 



77. Tests for Inulin. (a) Test the inulin solution with 

 iodine : only a faint brownish colour is given. (6) Add caustic 

 soda or potash to dry inulin in a test- tube : it dissolves without 

 being coloured, (c) Warm some inulin solution, then add a few 

 drops of alcoholic solution of orcin : an orange-red colour is given. 

 (d) To some inulin solution add a few drops of strong hydrochloric 

 acid, and coil ; cool, and add a few drops of alcoholic solution of 

 phloroglucin : a yellow-brown colour is given. Inulin is readily 

 distinguished from sugars by reactions (6), (c), and (d). 



(e) Cut sections from the pith of a fresh Dahlia tuber, and 

 examine in alcohol ; note the scanty cell-contents, with transparent 

 sap. Lay the sections in strong alcohol for about an hour, and 

 mount in glycerine ; note that the inulin has separated out in the 

 form of spherical crystal-like masses. 



(/) Cut a Dahlia tuber into pieces, and steep them in alcohol for 

 at least a week. (1) On examining sections in glycerine, note the 

 large sphere-crystals seated on the cell-wall and often extending 

 from cell to cell ; the longer the material has been in alcohol the 

 larger will these masses be. (2) To sections showing these inulin- 

 masses add iodine : the inulin is scarcely coloured. (3) Treat 

 other sections with water : the inulin is slowly dissolved. On 

 heating, the process of solution is hastened ; and during solution 

 the masses show a radiating structvire. (4) Treat other prepara- 

 tions with potash : they are dissolved more quickly than with 

 water. (5) Treat a section with 20 per cent, a-naphthol solution, 

 then add two or three drops of strong sulphuric acid : the crystals 

 dissolve with a violet colour. 



