4:2 PHYSIOLOGICAL CHEMISTRY 



The Fehling test will detect 0.1% glucose in a solution. 



Barfoed's Test. This test also depends upon the reduction of 

 a copper salt (copper acetate) by the sugar. It is performed, 

 however, in acid solution. Barfoed's reagent contains copper 

 acetate and acetic acid. The reducing action of the carbohy- 

 drates is very much less in acid than in alkaline solution. All 

 of the reducing carbohydrates will reduce Barfoed's reagent if 

 boiled a sufficient length of time, producing red cuprous oxide 

 as in the Fehling test. The monosaccharides, however, reduce 

 Barfoed's solution faster than do the disaccharides in equal 

 concentration, so that if properly used, this test may serve to 

 distinguish between monosaccharides and disaccharides. But a 

 concentrated maltose solution will reduce Barfoed's reagent 

 more rapidly than a weak glucose solution, so that this fact 

 should be borne in mind or erroneous conclusions may result. 



Almen-Nylander Test. Nylander's reagent contains bismuth 

 subnitrate, sodium potassium tartrate and potassium hydroxide. 

 The part played by each constituent is similar to that in Feh- 

 ling 's solution. The bismuth subnitrate is reduced to black, 

 metallic bismuth. The equations follow: 



Bi(OH) 2 N0 3 +KOH^Bi(OH) 3 +KN0 3 



2 Bi(OH) 3 +Sugar-Bi 2 +3H 2 0+(Sugar+30) 



Certain substances which interfere with Fehling 's test, have 

 no disturbing influence on the Nylander reaction (uric acid, 

 creatinine) so that this test is useful occasionally when the Feh- 

 ling test is of questionable value. A solution containing 0.08% 

 glucose will give a positive Nylander test. 



Haines' solution differs from Fehling 's solution in contain- 

 ing glycerine in place of sodium potassium tartrate. Its deli- 

 cacy is about equal to that of the Fehling test. 



Reduction of Carbohydrates. By the action of reducing 

 agents carbohydrates may be converted into alcohols, or on fur- 

 ther reduction they may give rise to compounds of the nature 

 of fatty acids. Such transformations apparently occur in the 

 cells of the body, for it is a well known fact that a 



