216 THE CARBOHYDRATES. 



This reaction depends, according to VILLE and DERRIEN, as well as to 

 v. EKENSTEIN and BLANKSMA 1 upon the formation of oxymethylfurfurol 

 which reacts with the a-naphthol. As oxymethylfurfurol is formed from 

 all hexoses, hence MOLISCH'S reaction is a general reaction for hexoses. 



DIAZOBENZENESULPHONIC ACID gives with a glucose 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 glucose and sodium carbonate, and this is converted into 

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

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

 of glucose toward certain pentose reactions has been given on page 209. 



A more complete description as to the performance of these several 

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



Glucose is prepared, pure, by inverting cane-sugar by the follow- 

 ing simple method of SOXHLET and TOLLENS, which is a modification of 

 SCHWARZ'S 2 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 glucose 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 glucose in animal fluids or extracts of tissues we may 

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

 mination, fermentation, and phenylhydrazine tests. For the quantitative 

 estimation 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 glucose. In regard to the difficulties 

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

 works. 



Mannoses. d-Mannose, also called seminose, is obtained with d-fructose on 

 the careful oxidation of rf-mannite. It is also obtained on the hydrolysis of 

 natural carbohydrates, such as salep slime and reserve cellulose (especially 

 from the shavings of the ivory-nut). It is dextrorotatory, readily ferments 

 with beer-yeast, gives a hydrazone not readily soluble in water, and an osazone 

 which is identical with that from d-glucose. 



d-Galactose (not to be mistaken for lactose or milk-sugar) is obtained on 

 the hydrolytic cleavage of milk-sugar, and by the hydrolysis of many other 



1 Bull. soc. chim. (4), 5, 895 (1909); Ber. d. d. chem. Gesellsch., 43, 2358 (1910). 



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



