PAVY, FEHLING. 175 



Pavijs modification of Fehlincfs process. 



Principle: Cuprous oxide is dissolved by NH 3 . A sufficient 

 quantity of NIL is added to Fehling to dissolve the Cu. 2 O 

 formed, the disappearance of the blue colour can thus be 

 better seen. The end of the reaction is more distinct. 



S.S. 120 cc Fehling + 400 CC NH 3 (0-88) + H 2 O to 1 litre. 10 CC = 

 pc ;p e hlmg = 0-005 g sugar. The solution keeps well in properly 

 stoppered bottles. It can be obtained in sealed tubes contain- 

 ing 10 CC . 



Process : 



1. Place 10 CC Pavy-Fehling in a flask fitted with a good 



cork through which two tubes pass. The one is short 

 and is joined to the nozzle of the burette by a rubber 

 junction, the other is bent to an angle outside the 

 cork and leads into the air. 



2. The burette, as in the former case, contains a 1 in 20 



dilution of the fluid under investigation. 



3. Boil the standard solution, and whilst it boils run in the 



sugary fluid from the burette with the precautions 

 mentioned. Note the disappearance of the colour, to 

 assist which hold a piece of white paper or a white 

 tile behind the flask. 

 Make a second and third estimation as before. 



Fermentation Process. Important. Glucose ferments ; 

 Glycuronic acid does not. To perform the estimation with 

 the greatest degree of accuracy, good hydrometers are required, 

 and should be employed at the temperature for which they 

 are graduated. 



Process : 



1. Take S.G. of urine, filter it, and place 100 CC in a flask. 



2. Add some yeast of the size of a pea, mix thoroughly. 



