PHYSIOLOGICAL CHEMISTRY 451 



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

 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 disappeared. 

 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. 



Gerrard's Method. The cyanide solution is prepared by adding 

 cautiously an approximately 5 per cent, solution of potassium cyanide 

 to 100 c.c. Fehling's solution diluted with 300 c.c. water, which is 

 kept boiling, until the blue colour of the solution has just disappeared. 

 The resulting liquid is cooled, diluted to exactly 500 c.c. and kept in 

 a stoppered bottle. 



For the titration 50 c.c. of the cyanide solution and 10 c.c. of 

 standard Fehling's solution are measured into a basin or flask, and 

 the diluted urine run in from a burette in exactly the same manner 

 as in Fehling's method. The urine required in the titration contains 

 0*05 grm. dextrose. 



Pavy's Method. The standard solution contains 120 c.c. Fehling's solution 

 and 300 c.c. strong ammonia per litre. 10 c.c. of this solution are equivalent 

 to 0*005 grm. dextrose. 



The nozzle of a burette is fitted to a small flask by means of a cork, through 

 which is also passed a short bent tube to allow of the escape of steam and 

 ammonia, when the flask is boiled. The urine is diluted exactly 10 to 50 

 times according to the amount of sugar present. The burette is filled with 

 this diluted urine, care being taken that there are no bubbles in the nozzle. 

 10 c.c. Pavy's solution and about an equal volume of water are placed in 

 the flask. The flask is now heated till it boils. The heating is continued 

 and the urine allowed to drop in from the burette at such a rate that 

 ebullition does not cease. When the colour in the flask is perceptibly 

 less, the rate of addition of drops is much reduced, but is continued until 

 all blue colour has disappeared. The first reading will be almost certainly 

 too great, so that other determinations must be made. In the later deter- 

 minations it is a good plan to run in fairly rapidly a quantity of urine, which 

 will be almost but not quite sufficient, to wait till the colour is constant and 



en very carefully and slowly to add drops from the burette till the blue 

 colour has quite disappeared. The amount of diluted urine employed should 

 not be less than 2 c.c. or more than 5 c.c. 



