202 THE CARBOHYDRATES. 



toses seem to be absorbed by human beings and in part utilized, but 

 they pass in part into the urine even when small quantities are taken. 1 

 The natural pentoses are reducing aldoses, and as a rule do not belong 

 to the sugars fermentable by yeast. Still, the observations of SAL- 

 KOWSKI, BENDIX, SCHONE and TOLLENS seem to indicate that the pen- 

 toses are fermentable 2 . They are readily decomposed by putrefaction 

 bacteria. With phenylhydrazine and acetic acid they give crystalline 

 osazones which are soluble in hot water, and whose melting-points and 

 optical behavior are important for the detection of the pentoses. On 

 heating with hydrochloric acid they yield furfurol, but no levulinic acid. 

 In this reaction furfuran is formed from the pentose molecule, and then 



HC CH 



from this its adehyde, the furfurol HC C.CHO. The furfurol pass- 



O 



ing over on distilling with hydrochloric acid can be detected by the aid 

 of aniline-acetate paper, which is colored beautifully red by furfurol. 

 In the quantitative estimation we can use the method suggested by TOL- 

 LENS, which consists in converting the furfurol in the distillate into 

 phloroglucide by means of phloroglucin and weighing (see TOLLENS and 

 KROBER, GRUND, BENDIX and EBSTEIN), or according to JOLLES 3 by 

 bisulphite and re titrating with iodine solution. In using these methods 

 it must be borne in mind that glucuronic-acid compounds also yield 

 furfurol under the same conditions. The two following pentose reac- 

 tions, as suggested by TOLLENS, are especially applicable. 



The orcin-hydrochloric acid test. Mix with the solution or the sub- 

 stance introduced into water an equal volume of concentrated hydro- 

 chloric acid, add some orcin in substance, and heat. In the presence 

 of pentoses the solution becomes reddish blue, then bluish green, and 

 on spectroscopic examination an absorption-band is observed between 

 C and D. If it is cooled and shaken with amyl alcohol, a bluish-green 

 solution which shows the same band is obtained. 



The phloroglucin-hydrochloric acid test. This test is performed in 

 the same manner as the above, using phloroglucin instead of orcin. The 

 solution becomes cherry -red on heating and then becomes cloudy and 

 hence a shaking out with amyl alcohol is very necessary. The red amyl- 



1 See Ebstein, Virchow's Arch., 129; Tollens, Ber. d. deutsch. chem. Gesellsch., 29, 

 1208; Cremer, 1. c.; Lindemann and May, Deutsch. Arch. f. klin. Med., 56; Salkowski, 

 Zeitschr. f. physiol. Chem., 30. 



2 Salkowski, Zeitschr. f. physiol. Chem., 30; Bendix, see Chem. Centralbl., 1.900, 1; 

 Schone and Tollens, ibid., 1901, 1. 



3 Bendix and Ebstein, 1. c., which contains the literature; Jolles, Ber. d. d. chem. 

 Gesellsch., 39 and Zeitschr. f . anal. Chem., 46. 



