CH. V.] GLUCOSE. 107 



98. To 2 cc. of a i per cent, solution add 2 cc. of 40 per cent, 

 sodium hydroxide. Heat to boiling and keep boiling for one and a 

 half minutes. To the hot solution add half its volume of Fehling's 

 solution. No reduction, or only a very slight one, is obtained. 



NOTE. Glucose is completely destroyed by boiling with sodium hydroxide. 



99. To 3 cc. of a i per cent, solution add a large " knife point " 

 of anhydrous sodium carbonate Boil for I minute, cool under the 

 tap Add half its volume of Fehling's solution, and allow to stand 

 without boiling. The Fehling's solution is reduced without boiling. 



NOTE. The experiment indicates that by the action of alkalies glucose is 

 converted to a material that will reduce Fehling's solution in the cold. Ex. 98 

 indicates that this material is destroyed by caustic alkalies. It will be seen 

 later (Ex. 118) that the disaccharides, lactose and maltose, differ from glucose in 

 that they reduce Fehling's in the cold after being boiled with either sodium 

 hydroxide or sodium carbonate. 



100. To 5 cc. of Benedict's solution in a test-tube, add about 

 eight drops of the sugar solution. Boil vigorously for one or two 

 minutes and allow the tube to cool spontaneously. The entire body 

 of solution will be filled with a precipitate, red, yellow, or green in 

 colour depending on the concentration of the sugar. (Benedict's test.) 



NOTES. i. Preparation of Benedict's solution for qualitative test. 

 Dissolve 173 grams, of sodium citrate and 90 grams, of anhydrous sodium 

 carbonate in about 600 cc. of distilled water by the aid of heat. Pour through 

 a folded filter and make up to 850 cc. Dissolve 17-3 grams, of crystallised 

 copper sulphate inioocc.of water and make up to 150 cc. Pour the carbonate 

 citrate solution into a large beaker and add the copper solution slowly, with 

 constant stirring. The mixed solution is ready for use and does not deteriorate 

 on long standing. 



2. Benedict's solution has certain advantages over Fehling's. For 

 example, it is not so readily reduced by uric acid or urates, nor by creatinine. 

 It is not reduced by chloroform, which is sometimes added to urine as a 

 preservative. It does not destroy a small amount of sugar, as Fehling's does 

 (see note 6 to Ex. 97). Also it can be used for testing urines for sugar in 

 artificial light, since it is the bulk and not the colour of the precipitate that is of 

 importance. 



3. Though Benedict's test is much better than Fehling's for the detection 

 of small amounts of glucose in urine, it is not quite so useful for other work. 

 The author claims that his test (Ex. 104) is the most sensitive for general use. 



101. To 5 cc. of the modified Barfoed's reagent in a test-tube 

 add i cc. of the 0-2 per cent, solution of glucose and stand the tube 

 in a beaker of boiling water. After three and a half minutes remove 

 the tube and examine it against a black background. A definite 

 reduction is obtained. Repeat the experiment with i cc. of the 



