GLUCOSE 99 



precipitate floating as a thin film on the surface of the liquid 

 indicates dextrose. This reaction is also given by levulose 

 and other hexoses but not by cane sugar or maltose. 



The reagent, which should be freshly made up, is prepared 

 by dissolving 5 grams of copper acetate, and 5 grams of 

 sodium acetate, in 100 c.c. of water containing i c.c. of glacial 

 acetic acid. 



7. The addition to the solution of picric acid and caustic 

 soda results in the formation of a blood-red coloration, due to 

 picramic acid. This reaction is also given by other reducing 

 sugars. 



8. On boiling the solution of glucose with an equal volume 

 of caustic potash, a yellow-brown colour results ; on acidifying 

 with dilute nitric acid the colour lightens and a smell of burnt 

 sugar is produced. 



9. Glucose reacts with phenylhydrazine to give an osazone. 

 To 5 c.c. of an approximately 5 per cent solution of glucose, 

 add 4 or 5 drops of phenylhydrazine and about the same 

 amount of glacial acetic acid. (If phenylhydrazine hydro- 

 chloride is used, add about enough solid to cover a threepenny 

 piece and an equal .quantity of sodium acetate.) Place the 

 mixture in a boiling water bath for about half an hour and 

 then remove ; a golden yellow crystalline precipitate will have 

 been formed. On examination under the microscope the 

 needle-shaped crystals will be seen to be gathered together 

 in clusters resembling wheat sheaves. Glucosazone melts 

 at 204-205° with decomposition ; it is insoluble in water but 

 soluble in alcohol, the solution being laevo-rotatory in contra- 

 distinction to that of maltose which is dextro-rotatory. 



The constitutional formula of glucose is given on p. 84. 



Microchemical Tests. 



For microchemical tests for sugars, the reduction of copper 

 salts in the presence of excess of alkali is generally employed, 

 but these are not altogether satisfactory, owing to the amount 

 of diffusion which takes place, and also because sucrose, if its 

 presence in a tissue be suspected, must first be hydrolysed by 

 boiling with acid before the reduction will take place. 



