V] CARBOHYDRATES 61 



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

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

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

 Filter off 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 

 begin to deposit. Then pour into an equal volume of alcohol, and allow to stand for 

 one or two days. The crude precipitate of inulin is filtered off, dissolved in a small 

 amount of water, and reprecipitated with alcohol. It can be washed with alcohol and 

 ether and dried over sulphuric acid. 



The Artichoke {Helianthus tuberosus) may also be used, about 12 tubers being 

 necessary. 



Ba^pt. 60. Tests for inulin. Make a solution of some of the inulin prepared in 

 Expt. 59 in hot water. It will readily dissolve giving a clear solution. With the 

 solution make the following tests : 



{a) Make a very dilute solution of iodine and add to it a drop or two of inulin 

 solution : the brown colour will be unaffected. 



(6) Boil some inulin solution with a little Fehling : no reduction takes place. 



If the inulin solution which is being used should reduce Fehling it indicates that 

 sugar is present as impurity. If this is the case, then a little of the solid inulin 

 should be washed free from sugar by means of alcohol before proceeding with the 

 following test. 



(c) To 5 c.c. of Seliwanoff^s solution add a few drops of inulin solution and boil. 

 A red coloration is formed. This reaction is also due to the presence of laevulose 

 (see laevulose, p. 53), 



Expt. 61. Hydrolysis of inulin. Some inulin is dissolved in very dilute hydrochloric 

 acid (about 0*5 %) and heated on a water-bath for half an hoiir in a round-bottomed 

 flask provided with an air condenser (see p. 46). The solution is then neutralized 

 with sodium carbonate and concentrated on a water-bath. With the concentrated 

 solution make the following tests : 



(a) Boil with a little Fehling : the solution is rapidly reduced. 



(6) Make the osazone test (see p. 50). Glucosazone crystals will be found to 

 be formed on microscopic examination. (Laevulose forms the same osazone as 

 glucose.) 



(c) Make the test (c) of the last experiment. A positive result will be given. 



M ANNANS. 



The mannans which have already been mentioned (see p. 52) ar^ 

 condensation products of the hexose, mannose. They occur most fre- 

 quently, either mixed, or in combination, with the condensation products 

 of other hexoses and pentoses (glucose, galactose, fructose and arabinose) 

 as galactomannans, glucomannans, fructomannans, mannocelluloses, etc. 

 Such mixtures or compounds of which mannans form a constituent are 

 widely distributed in the seeds of many plants, i.e. Palms (including the 

 Date-palm), Asparagus (Ruscus), Clover (Trifolium), Coffee Bean (Goffea 



