ELEMENTARY CHEMICAL PHYSIOLOGY 207 



when the solution to be tested contains only a small amount of 

 dextrose or other reducing substance. Boil a few c.c. of Fehling's 

 solution in a test tube. Add the dextrose solution drop by drop, 

 with continued boiling, until reduction results, as evidenced by 

 the diminution of the blue colour and the formation of an orange 

 red precipitate. 



EXPERIMENT III. Benedict's Test. To 5 c.c. Benedict's (quali- 

 tative) reagent 1 add a few drops of dextrose solution and boil 

 hard for several minutes. According to the amount of sugar present 

 in the solution used the colour varies from greenish to red. 



EXPERIMENT IV. Nylander's Test. To about 5 c.c. of dextrose 

 solution in a test tube add about 1 c.c. of Ny lander's reagent (a 

 solution containing 10 per cent, caustic soda, 4 per cent. Rochelle 

 salt and 2 per cent, bismuth subnitrate). Boil for two minutes. A 

 black precipitate of bismuth forms. Some substances (creatinine, 

 uric acid) which reduce Fehling's solution do not give this test. 

 As regards the sugars, however, where Fehling's test is positive 

 this test will also be positive. 



EXPERIMENT V. Boil glucose solution with Barfoed's 2 solution. 

 Add two drops of the sugar solution to about 5 c.c. of Barfoed's 

 solution in a test tube and boil for about half a minute. Remove 

 from the flame, shake gently for 10-15 seconds and again boil. 

 The appearance of the red coppzr oxide indicates the presence of a 

 monosaccharide. (The reduction which takes place with Barfoed's 

 solution is, as a rule, very slight.) 



77. Monosaccharides form compounds called Osazones, with Phenyl 

 Hydrazine. The compounds are very useful in identifying the 

 various forms of sugars, as each sugar forms a slightly different 

 compound. 



EXPERIMENT VI. The production of osazones. Add -25 grm. 

 (enough to cover a sixpence) of phenyl-hydrazine hydrochloride and 

 an equal bulk of sodium acetate crystals to about 10 c.c. of a 1 per 

 cent, solution of dextrose. Warm gently till everything is dissolved, 

 and then place for half an hour in a boiling water bath. Allow to 

 cool, when a yellow precipitate of glucosazone will separate out. 

 Examine this under the microscope, and notice that, the precipitate 

 is composed of branching needle-shaped crystals arranged in rosettes 

 or sheaves (Fig. 173). 



The chemical reaction takes place in two stages, the intermediate body 

 being called a hydrazone. 



1 Benedict's (qualitative) reagent. Anhydrous sodium carbonate lOOgrms. 

 and sodium citrate 175 grms. are dissolved in about 500 c.c. water; to this 

 mixture is added 17-3 grms. crystalline copper sulphate dissolved in 100 

 c.c. water, gradually, and with frequent shaking. Make up to 1 litre. 

 The advantage of this solution is that it does not deteriorate on keeping, it 

 does not destroy traces of sugar, and is not reduced by chloroform. 



2 Barfoed solution : 50 grms. cupric acetate and 50 grms. sodium acetate 

 are dissolved in water, 5 c.c. glacial acetic acid added and the solution made 

 up to 1 litre with water. 



