PENTOSE REACTIONS. 209 



HC CH 



I! II 



from this its aldehyde, 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 or xylidine acetate paper, which is colored a beautiful 

 red by furfurol. In the quantitative estimation we can use the method 

 suggested by TOLLENS, 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 1 by bisulphite and retitrating 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 

 reactions, as suggested by TOLLENS, are especially applicable. 



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

 introduced into water an equal volume of concentrated hydrochloric 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-alcohol solution shows an 

 absorption-band between D and E. The orcin test is better for several reasons 

 than the phloroglucin test (SALKOWSKI and NEUBERG 2 ). In regard to the use 

 of these tests in urine examination see Chapter XIV. 



Many modifications of these tests have been suggested. BRAT 3 performs 

 the orcin reaction by the addition of NaCl and heating to only 90-95. BIAL 4 

 uses a hydrochloric acid containing ferric chloride for the orcin test and claims 

 to get a greater delicacy. On too strong and too long heating (l|-2 minutes), 

 when using this modification, a confusion with sugars of the six carbon series may 

 occur (BiAL, VAN LEERSUM). S According to R. ADLER and 0. ABLER the phlo- 

 roglucin and orcin tests can be made with glacial acetic acid and a few drops 

 hydrochloric acid instead of with the hydrochloric acid alone. These investigators 

 also use a mixture of equal volumes of aniline and glacial acetic acid as a reagent 

 for pentoses. On the addition of a little pentose to the boiling mixture a beautiful 

 red color of furfurol-anilme acetate is obtained. A. NEUMANN 6 performs the 

 orcin test with glacial acetic acid and adds concentrated sulphuric acid drop 

 by drop. On following the exact instructions not only do the pentoses give 

 this reaction, but also glucuronic acid, glucose, and fructose give characteristic 



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

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



2 Salkowski, Zeitschr. f. physiol. Chem., 27; Neuberg, ibid., 31. 



3 Zeitschr. f. klin. Med., 47. 



4 Deutsch. med. Wochenschr., 1902 and 1903, and Zeitschr. f. klin. Med., 50. 



5 Bial, Zeitschr. f. klin. Med., 50; van Leersum, Hofmeister's Beitrage, 5. 



6 R. and O. Adler, Pfliiger's Arch., 106; A. Neumann, Berl. klin. Wochenschr., 

 1904. 



