PHYSIOLOGICAL CHEMISTRY 



295 



TABLE FOR CALCULATION OF AMOUNT OF DEXTROSE FROM 

 HYDROXYLAMIN SOLUTION USED IN BANG'S METHOD. 



exist as polysaccharides called pentosanes. Thus, in gum arabic there is a 

 pentosane which yields -arabinose when hydrolysed by heating with- mineral 

 acid, and in wood or bran another pentosane yields Z-xylose on similar treatment, 

 which is the variety of pentose present in the nucleic acid of animal cells. 

 Pentose sometimes occurs in the urine the condition being called pentosuria 

 the variety being racemic arabinose (inactive optically). From what source this 

 is derived is difficult to determine, for it is independent of the pentoses in the 

 food, and its structure is different from that found present in the tissues. It is 

 mostly combined with urea. 



EXPERIMENT. Hydrolyse gum arabic by heating a solution of it in a water 

 bath for twenty minutes with 5 % HC1. Arabinose is formed. After neutralising, 

 apply reduction and yeast fermentation tests to portions of the solution. To 

 another portion apply the following characteristic test for pentoses (Tollens). 

 Add phloroglucin (C 6 H 3 (OH) 3 ) in small quantities at a time till no more dissolves 

 to a solution of about 5 c. c. of equal parts of concentrated HC1. and water. Then 

 add a few drops of the arabinose solution and warm until a red colour develops. 

 Examine with the direct vision spectroscope when an absorption band will be 

 seen between D. and E. lines. By further heating, a precipitate forms which 

 becomes dissolved in amyl alcohol when this is shaken with the solution. The 

 amyl alcoholic solution shows the above spectrum very clearly. Tollens' test can 

 be applied to urine. Repeat this test, using dextrose solution. 



EXPERIMENT. Heat about 5 c.c. of Bial's reagent (500 c.c. HCL, sp. gr. 

 1*151, 1 grm. orcinol, 25 drops 10% ferric chloride solution) to boiling in a test 

 tube, and run in not more than 1 c.c. of the pentose- containing solution, and 

 again heat just to boiling point. A greenish-blue colour rapidly develops. This 

 colour can be extracted with amyl alcohol, when it shows an absorption band in 

 the red. 



Repeat this test, using a dilute solution of dextrose instead of pentose, when 

 dractically no colour change will occur. 



