XXIII.] QUANTITATIVE ESTIMATION OF SUGAR. 143 



((/.) Indigo-Carmine Test. To the urine add sodium carbonate 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. 



(//.) Repeat Molisch's test (Lesson I.). 



6. Preparation of Fehling's Solution. Solution A. 34.64 grams of pure 

 crystalline cupric sulphate are powdered and dissolved in 500 cc. of distilled 

 water. Solution B. In another vessel dissolve 173 grams of Rochelle salts 

 (sodio-potassium tartrate) in 100 cc. of pure caustic soda, sp. gr. 1.34, and add 

 water to make 500 cc. Keep the two solutions separate in stoppered bottles, 

 and mix them as required. On mixing equal quantities of A and B, a clear deep 

 blue fluid is obtained, the Rochelle salt holding the cupric hydrate in solution. 



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

 pose, 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 

 and glycuronic acids reduce cupric oxide. In all cases see that there is an 

 excess of the test present. 



LESSON XXIII. 

 QUANTITATIVE ESTIMATION OF SUGAR. 



1. By the Saccharimeter. 



Study the use of some form of saccharimeter. The portable form made by 

 Zeiss is very convenient. A coloured urine must first be decolorised by acetate 

 of lead [Lesson XX. 13 (d.)]. 



2. Diabetic Urine. Volumetric Analysis by Fehling's Solution. 



io cc. of Fehling's solution = .05 gram of sugar. 



(a.) Ascertain the quantity passed in twenty-four hours. 



(A.) Filter the urine, and remove any albumin present by boiling 

 and nitration. 



(c.) Dilute io cc. of Fehling's solution with about five to ten 

 times its volume of distilled water, and place it in a white porcelain 

 capsule on a wire gauze support under a burette. [It is diluted 

 because any change of colour is more easily observed.] 



(d.) Take 5 cc. of the diabetic urine, add 45 cc. of distilled 

 water, and place the diluted urine in a burette. Diabetic urine 

 usually contains 4 p.c. or more of dextrose, and as the solution to 

 be tested should not contain more than 0.5 p.c. of dextrose, hence 

 the necessity for diluting the urine. 



(e.) Boil the diluted Fehling's solution, and whilst it is boiling 

 gradually add the diluted urine from the burette until all the 

 cuprous oxide is precipitated as a reddish powder, and the super- 



