192 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



This test is given by glucose and other monosaccha rides, but not 

 by lactose and maltose. It may be used for distinguishing between 

 glucose and the disaccharides, but the reagent must be freshly prepared, 

 otherwise maltose and lactose will also reduce it. 



(c) Bismuth. 



BoettgeSs Test. On boiling some glucose solution with a few crystals 

 of bismuth subnitrate and twice the quantity of sodium carbonate, the bismuth 

 hydrate first formed becomes reduced to metallic bismuth ; the precipitate 

 becomes grey or black in colour. 



NylandeSs Test. If 5 parts of glucose solution be boiled with i part 

 of Nylander's reagent (p. 613) for 2-5 minutes, reduction occurs and a black 

 precipitate settles out on cooling. 



These reactions are particularly useful for detecting small quantities of 

 glucose in urine. The uric acid and creatinine in urine also reduce Fehling's 

 solution, but not Nylander's solution. 



(8) Reduction of Dye-stuffs. 



(i) On adding picric acid and caustic soda to a solution of glucose and 

 warming, a blood- red colour is formed due to the formation of picramic acid. 



(ii) On warming a dilute solution of sodtum sulphindigotate, made alkaline 

 with sodium carbonate, with some glucose solution, the blue colour changes to 

 green, purple-red and finally yellow. The blue colour returns on cooling and 

 shaking the solution with air. 



(iii) If some glucose solutic-n be added to about 5 c.c. of a solution of 

 safranin and the mixture boiled, the opaque red colour changes to light 

 yellow. 



(9) Formation of Osazones. The reaction of glucose and other 

 reducing sugars with phenylhydrazine is very characteristic, as it serves 

 for the identification of the different carbohydrates. Glucose reacts 

 with phenylhydrazine in acetic acid solution in two stages ; the phenyl- 

 hydrazone is first formed : 



CH 2 OH . CHOH . CHOH . CHOH . CHOH . CHO + H 2 N . NH . C B H fi = 

 H 2 + CH 2 OH . CHOH . CHOH . CHOH . CHOH . CH : N . NH . C 6 H 5 . 



This is a colourless compound soluble in water. 



The secondary alcohol group next to the aldehyde group is oxidised 

 by excess of the reagent to the ketone group, which reacts with phenyl- 

 hydrazine and an osazone is formed : 



CH 2 OH . CHOH . CHOH . CHOH . CHOH . CH : N . NH . C fi H 5 + H 2 N . NH . C,.H 5 = 

 CH 2 OH. CHOH. CHOH. CHOH. CO. CH: N . NH . C 6 H 5 + NH 3 + H 2 N . C 6 H B 



CH 2 OH . CHOH . CHOH . CHOH . CO . CH : N . NH . C fi H 5 + H 2 N . NH . C 6 H 5 = 

 CH 2 OH . CHOH . CHOH . CHOH . C( : N . NH . C 6 H 5 ) . CH : N . NH . C B H 5 + H 2 O. 



On adding equal quantities of phenylhydrazine and glacial acetic 

 acid (5 to 10 drops of each), or I part of phenylhydrazine hydrochloride 

 and 2 parts pf sodium acetate to about 20 c.c. of glucose solution and 

 warming in a boiling water-bath for half to one hour, a yellow crystalline 

 mass of phenylglucosazone is formed. The solution is allowed to cool, 

 the crystals are filtered off and examined under a microscope. They 

 consist of long needles arranged in sheaves as in Fig. 39. 



