CHAPTER III 

 CARBOHYDRATES 



Study the reactions of the physiologically important carbohy- 

 drates in solutions of the pure substances, as this method is more 

 convenient for laboratory purposes than the preparation of the 

 materials from the tissues or body fluids in which they occur. 



I. Monosaccharid.es 



/. HEXOSES. This group includes the monosaccharides of 

 greatest physiological importance, dextrose, levulose and galac- 

 tose. 



a Dextrose. (Glucose.) 



i. Solubility. Test the solubility of dextrose in water, 95% 

 alcohol and ether. (Be careful of fire.) To test the solubility of 

 a substance in a given solvent, take a small amount of the solid 

 in a test tube and to it add a few cubic centimeters of the liquid. 

 In case the solid does not completely dissolve, filter and test the 

 filtrate for the substance in question to see if any has dissolved. 

 This may be done either by evaporating the solution to dry ness, 

 or by chemical means. If there is any doubt as to the solubility 

 of dextrose in the solvents tried, filter and evaporate to dryness 

 on the steam bath. A residue indicates that a portion of the 

 material has dissolved. 



Test the solubility of dextrose in alcohol diluted with an equal 

 volume of distilled water. Dextrose is soluble in dilute alcohol. 

 It thus will not be precipitated from aqueous solution by the ad- 

 dition of alcohol. This is a point of difference from dextrin, 

 which is precipitated by alcohol. 



ii. F calling's Test. Fehling's reagent is made up in two parts, 

 A and B, which are mixed in equal amounts immediately before 



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