36 PHYSIOLOGICAL CHEMISTRY. 



in the proportion of one molecule of glucose to five molecules 

 of crystallized copper sulphate. 



It was formerly held that the reaction was a perfectly 

 definite and simple one, and could be expressed in this manner, 

 but it is now known that the dilution of the solutions is a very 

 important factor in determining the amount of copper reduced. 

 The best conditions to be employed in practice have been deter- 

 mined by Soxhlet, who found the reducing power of several 

 sugars to vary as follows, when they were tested in solutions 

 of i per cent strength: 



0.5 gm. of invert sugar in i per cent solution reduces 101.2 cc. of 

 Fehling's solution, undiluted. 



0.5 gm. of invert sugar in i per cent solution reduces 97.0 cc. of 

 Fehling's solution, diluted with 4 volumes of water. 



0.5 gm. of glucose in i per cent solution reduces 105.2 cc. of Fehling's 

 solution, undiluted. 



0.5 gm. of glucose in i per cent solution reduces 101.1 cc. of Fehling's 

 solution, diluted with 4 volumes of water. 



0.5 gm. of milk sugar in i per cent solution reduces 74 cc. of Fehling's 

 solution, undiluted. The reducing power in diluted solution is the same. 



0.5 gm. of maltose in i per cent solution reduces 64.2 cc. of Fehling's 

 solution, undiluted. 



0.5 gm. of maltose in i per cent solution reduces 67.5 cc. of Fehling's 

 solution, diluted with 4 volumes of water. 



The oxidizing power of i cc. of Fehling's solution with each kind of 

 sugar may be tabulated as follows, assuming the sugars to be in solutions 

 of approximately i per cent strength when acted upon. 



One cubic centimeter of Fehling's solution oxidizes : 



When When Diluted with 



Undiluted. 4 Vols. of Water. 



Glucose 4.75 mg. 4.94 mg. 



Invert Sugar 4.94 " 5.15 " 



Milk Sugar 6.76 " 6.76 " 



Maltose 7.78 " 7.40 " 



The practical application of the test is best shown by an experiment. 



Ex. Measure out accurately into a flask holding about 250 cc., 25 cc. 

 of the copper solution and the same volume of the alkaline tartrate. Heat 

 the mixture, or Fehling's solution, on a wire gauze and note that it 

 remains clear. Fill a 50 cc. burette with a dilute glucose solution and 

 run 10 cc. into the hot liquid. Boil two minutes, shaking the flask con- 

 tinuously, and allow the mixture to settle. If the supernatant liquid ap- 

 pears yellow the mixture indicates that the sugar solution is much too 



