ELEMENTARY CHEMICAL PHYSIOLOGY 275 



Lactose and pentose do not give a positive result by this test. 



2. The Phenyl Hydrazine Test. The method of employing this 

 is described on p. 207. The obtaining of characteristic dextrosazone 

 crystals is positive evidence of the presence of dextrose ; glycuronic 

 acid (p. 278) also gives crystals, but less readily. 



Estimation of Dextrose in Urine. The polarimeter (see p. 212) 

 may be employed for the estimation of dextrose in urine. The main 

 objection to its use is that optically active bodies besides dextrose, 

 e.g. glycuronic acid and oxybutyric acid, which are laevo-rotatory, 

 occur in diabetic urine, and therefore to a certain extent vitiate 

 the result. The other method is to determine the reducing power 

 of the urine. 



Fehling's Method. The standard solution contains 34-64 gms. pure 

 crystallised copper sulphate, 180 gms. Rochelle salt and 70 gms. 

 caustic soda per litre. 10 c.c. of this solution are equivalent to 

 0-05 grm. dextrose. 



The urine is diluted exactly 10 or 20 times according to the 

 amount of sugar present and placed in a burette. 10 c.c. of the 

 standard solution are measured with a pipette into a porcelain 

 basin, diluted with 40 to 50 c.c. water and heated to boiling. The 

 solution is kept just boiling, and the diluted urine run in carefully 

 with stirring, until the blue colour of the solution has just dis- 

 appeared. From the volume of diluted urine required in the 

 titration the amount of dextrose in grammes present in 100 c.c. 

 of the original urine is calculated. Several determinations must be 

 made. A flask heated on a water-bath may be substituted for the 

 basin in order to minimise the risk of oxidation of cuprous oxide. 



Either of the two following methods may be used. They are 

 both easy to carry out and both give excellent results. They are 

 to be preferred to the Fehling method. 



1. Folin's Method. Reagents. (1) Copper sulphate solution 

 containing 59 gms. CuSO 4 ,5H 2 and 2 c.c. of concentrated sul- 

 phuric acid per litre (to prevent precipitation of copper hydrate by 

 traces of alkali from the glass bottle). (2) Saturated solution of 

 sodium carbonate containing 14-20 per cent. Na 2 C0 3 . (3) Alkaline 

 phosphate mixture. Mix thoroughly in a mortar 200 gms. crystal- 

 lised disodium phosphate (HNa 2 P0 4 ,12H 2 0) and 50 gms. of 

 sodium (or 60 gms. potassium) thiocyanate. To the semi-liquid 

 paste which is formed add 100-110 gms. anhydrous sodium carbonate 

 and mix until the compound forms a granular powder. Keeps 

 indefinitely, but should be kept in stoppered bottles. Folin recom- 

 mends that the small 5 c.c. burette used for holding the sugar 

 solution should be provided with a fine accessory tip attached by 

 rubber tubing to the burette so that the drops will be small and 

 uniform. 



Measure out approximately 5 gms. (not less than 4-5 gms. nor 

 more than 5 -5 gms.) of the phosphate mixture into a large (boiling) 

 test tube containing 5 c.c. of the copper solution and 1 c.c. of the 



