DEXTROSE. 209 



has disappeared, a precipitate of benzoic-acid ester of dextrose will be 

 produced which is insoluble in water or alkali (BAUMANN l ) . 



If J-l cc. of a dilute watery solution of dextrose is treated with a 

 few drops of a 10 per cent alcoholic solution (free from acetone) of a- 

 naphthol, the liquid is colored a beautiful violet on the addition of 1-2 

 .cc. of concentrated sulphuric acid (MOLISCH). According to RsiNBOLD 2 

 this reaction depends first upon the formation of a volatile substance 

 which gives a bluish-violet color with a-naphthol and sulphuric acid 

 in the warmth. On further heating furfurol is also produced, which 

 gives a raspberry-red to ruby-red coloration. 



DIAZOBENZENESULPHONIC ACID gives with a dextrose solution made alkaline 

 with a fixed alkali a red color, which after 10-15 minutes gradually changes to 

 violet. ORTHONITROPHENYLPROPIOLIC ACID yields indigo when boiled with a 

 small quantity of dextrose arid sodium carbonate, and this is converted into 

 indigo-white by an excess of sugar. An alkaline solution of dextrose is colored 

 deep red on being warmed with a dilute solution of PICRIC ACID. The behavior 

 of dextrose toward certain pentose reactions has already been given on page 

 203. 



A more complete description as to the performance of these several 

 tests will be given in detail in a subsequent chapter (on the urine). 



Dextrose is prepared pure by inverting cane-sugar by the follow- 

 ing simple method of SOXHLET and TOLLENS, being a modification of 

 ScHWARz's 3 method: 



Treat 12 liters 90-per cent alcohol with 480 cc. fuming hydrochloric 

 acid and warm to 45-50 C.; gradually add 4 kilos of powdered cane-sugar, 

 and allow to cool after two hours, when all the sugar will have dissolved 

 and been inverted. To incite crystallization, some crystals of anhydrous 

 dextrose are added, and after several days the crystals are sucked dry by 

 the air-pump, washed with dilute alcohol to remove hydrochloric acid, and 

 crystallized from alcohol or methyl alcohol. According to TOLLENS it is 

 best to dissolve the sugar in one-half its weight of water on the water- 

 bath and then add double this volume of 90-95-per cent alcohol. 



In detecting dextrose in animal fluids or extracts of tissues we may 

 make use of the above-mentioned reduction tests, the optical determina- 

 tion, fermentation, and phenylhydrazine tests. For the quantitative esti- 

 mation the reader is referred to the chapter on the urine. Those liquids 

 containing proteins must first have these removed by coagulation with 

 heat and addition of acetic acid, or by precipitation with alcohol or 

 metallic salts, before testing for dextrose. In regard to the difficulties 

 of operating with blood and serous fluids we refer the student to larger 

 works. 



1 Ber. d. deutsch. chem. Gesellsch., 19; also Kueny, Zeitschr. f. physiol. Chem., 14, 

 and Skraup, Wien. Sitzungsber., 98, (1888). 



2 Molisch, Monatshefte f. Chem., 7, and Centralbl. f. d. med. Wissensch., 1887, 

 pp. 34 and 49; Reinbold, Pfliiger's Arch., 103. 



3 Tollens, Handbuch der Kohlehydrate, 2. Aufl. I, 39. 



