62 THE CARBOHYDRATES 



2. Nylander's Test. When boiled with a solution of glucose 

 Nylander's reagent turns brown and finally black owing to the 

 precipitation of bismuth oxide and metallic bismuth. 



The reagent is prepared by dissolving 2 grams of bismuth 

 oxynitrate and 4 grams of Rochelle salt in 100 grams of 10 

 per cent caustic soda solution. 



3. Add to the solution basic lead acetate and ammonia. 

 If glucose be present, a white precipitate comes down, which 

 turns red. This reaction is not given by cane sugar. 



4. Add to the solution a little copper sulphate solution 

 and an excess of caustic potash. On warming, a yellow to red 

 precipitate is formed. This reaction also is given by levulose 

 and maltose, but not by saccharose. 



5. On warming with Fehling's solution, a red precipitate 

 is given by dextrose, levulose and maltose, but not by 

 saccharose. 



6. Add a little Barfoed's reagent and warm. A red 

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

 indicates dextrose. This reaction is also given by levulose 

 but not by cane sugar or maltose. 



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

 by dissolving 6'5 grams of copper acetate in 100 c.c. of water 

 containing I gram 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 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 



