54 CARBOHYDRATES AND THEIR [ch. 



Expt. 49. Detection of pentose from pentosans in bran, sawdust and strav. Take 

 a small quantity of bran and boil it up several times with 98 % alcohol, filtering off' 

 the alcohol after each treatment. This should remove any sugars or glucosides 

 present. Allow the alcohol to evaporate oft" from the bran, and then make the 

 following tests for pentoses (see Ex^jt. 38) : 



(a) Heat, for about one minute, a small quantity of the bran in a test-tube, with 

 sufficient concentrated hydrochloric acid to cover it. Care should be taken not to 

 char the material. Then add as much solid orcinol as will lie on the tip of a pen- 

 knife. Heat gently again for a few seconds. Then add one or two drops of strong 

 ferric chloride solution ; a green coloration will be produced. Add amyl alcohol and 

 the green colour will pass into the alcohol. 



(6) Heat again another portion of the bran with the same quantity of concentrated 

 hydrochloric acid in a test-tube, but this time heat more strongly. After heating a 

 few minutes place a j)iece of filter-paper soaked in a solution of aniline acetate in the 

 mouth of the test-tube. A cherry-red coloration will denote the formation of 

 furfural. 



The above method and tests with bran may be repeated in exactly the same way 

 using sawdust or straw. 



Expt. 50. Preparation of xylan from sawdust. Extract one kilo of sawdust with 

 4 litres of 1-2 % ammonia solution for 24 hrs. Then filter off" the ammoniacal solution 

 through muslin and repeat the extraction. The xylan is insoluble in ammoniacal 

 solution, and in this way colouring matters are removed. Finally wash the .sawdust 

 well with water and press dry from the liquid. Then add to the .sawdust sufficient 

 5% caustic soda solution to make a thick mush (about 1000-1.500 c.c.) and allow it 

 to stand for 24 hrs. in a warm place. The alkaline solution is then pressed out 

 through calico and filtered through filter-paper. To the clear filtrate add an equal 

 volume of 96 "/^ alcohol which will precij^itate the xylan as a sodium compound. 

 Filter off" this precipitate, wash with alcohol, and decomjaose with alcohol to which 

 a little strong hydrochloric acid has been added to remove the sodium. The free 

 xylan is again washed with alcohol, and can be dried by washing with absolute 

 alcohol and ether and finally in a desiccator. It is a dirty-white powder which is 

 almost insoluble in water. Make th"e tests for pentoses (see Expt. 38) on a little of 

 the solid xylan. The reaction will be given in each case. 



Expt. 51. Hydrolysis of xylan. Put the xylan obtained in the last experiment 

 in a round-bottomed flask fitted with an air condenser (.see ]>. 45). Add 100 c.c. of 

 4 % sulphuric acid and heat on a water-bath for 4 hrs. Neutralize the solution with 

 calcium carbonate, filter from calcium sulphate and concentrate on a water-bath. 

 Test a portion for pentoses (see Expt. 38) and a positive reaction will be obtained. 

 To a .small quantity add also a few drops of Fehling's solution and l)oil. Reduction 

 will take place. 



To the remainder of the xylose solution add bromine (see p. 45) gradually until 

 there is excess. Then remove the excess of bromine by warming on a water-bath. 

 Neutralize the solution, which contains xylonic acid, with cadmium carbonate and 

 evaporate on a water-bath. Extract the residue with alcohol and filter. On concen- 

 trating the alcoholic extract, white prismatic needles of cadmium xylonate separate 

 out. 



