116 CHEMICAL PHYSIOLOGY. 



(c.) Fehling's solution is alkaline potassio-tartarate of 

 copper (K 2 Ou2C 4 H 4 O 6 ). Place some Fehling's solution in a 

 test-tube and boil it. If no discoloration (yellow) takes 

 place, it is in good condition. Add a few drops of the 

 suspected urine and boil, when the mixture suddenly turns 

 to an opaque yellow or red colour, which indicates the 

 presence ot a reducing sugar. 



(d.) Bottger's Test. Mix the urine with an equal volume 

 of sodic carbonate solution, add a little basic bismuthic 

 nitrate, and boil for a short time. A grey or black deposit 

 indicates the presence of a reducing sugar. 



(e.) Picric Acid. To the urine add an equal volume of a 

 saturated watery solution of picric acid, and then caustic 

 potash. Boil, an intensely deep red or reddish-brown colour 

 indicates the presence of a reducing sugar. The larger the 

 amount of sugar, the deeper the tint. The coloration is 

 due to the formation of picramic acid. 



(/) Indigo- Carmine Test. To the urine add sodic car- 

 bonate solution and indigo-carmine solution until a blue 

 colour appears. Boil, and a yellow colour is obtained, 

 if sugar be present, owing to the reduction of indigo-blue to 

 indigo-white. Pour the fluid into a cold test-tube, when the 

 blue colour is restored, a beautiful play of colours intervening 

 between the yellow and the blue. This is not a satisfactory 

 test. 



6. Preparation of Fehling's Solution. 34-64 grammes of pure 

 crystalline cupric sulphate are powdered and dissolved in 200 cc. 

 of distilled water ; in another vessel dissolve 173 grammes of 

 Rochelle salts in 480 cc. of pure caustic soda, specific gravity 

 1-14. Mix the two solutions, and dilute the deep coloured fluid 

 which results to 1 litre. It is better to keep the two solutions 

 separate in stoppered bottles, and mix them as required. 



N.B. Fehling's solution ought not to be kept too long ; it is 

 apt to decompose, and should therefore be kept away from the 

 light, or protected with opaque paper pasted on the bottle. Some 

 other substances in urine e.g., uric acid reduce cupric oxide. 

 In all cases see that there is an excess of the test present. 



