PHYSIOLOGICAL CHEMISTRY 275 



EXPERIMENT VI. Boil some glucose solution with Barfoed's solution 

 (acid cupric acetate). Reduction occurs. This test applies to the 

 monosaccharides only. Disaccharides do not reduce Barfoed's solution. 



EXPERIMENT VII. Demonstrate that dextrose also reduces ammonia- 

 cal silver nitrate to metallic silver. 



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. 

 They are also of great interest because it was by producing them 

 that Emil Fischer was able to convert one sugar into another and 

 thus to discover the chemical constitution of the sugars. 



EXPERIMENT VIII. 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% 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. 221). 



The chemical reaction takes place in two stages, the intermediate 

 body being called a hydrazone. 



The formula for osazone is 



CH 2 OH 



(CHOH) 3 



C = N-NH-C 6 H 5 

 C = N-NH-C 6 H 5 



H 



The excess of sodium acetate in the above mixture reacts with 

 the phenyl-hydrazine hydrochloride so as to form the acetate. 



When it is desired to produce osazones from dilute sugar solutions, a more 

 certain way to proceed is as follows : Mix two drops of phenyl-hydrazine (fluid) 

 with ten drops glacial acetic acid and add to this 5 c.c. of the sugar solution, 

 shake, and place the test tube for one hour in the boiling water bath. After 

 cooling examine under the microscope for the crystals. With stronger sugar 

 solutions this method yields crystals after a few minutes' heating. 



The advantage of the phenyl-hydrazine hydrochloride is that it does not 

 readily decompose on keeping, whereas the free base does. 



The osazone crystals are valuable for distinguishing between the different 

 sugars. Besides microscopical examination, a determination of the melting point 



