276 PRACTICAL PHYSIOLOGY 



carbonate solution. Heat gently about 60, with shaking, until 

 all the salts except for a few isolated particles of sodium carbonate 

 have dissolved. A practically clear solution is usually obtained 

 in less than one minute. Add a glass bead to prevent bumping 

 when heating with sugar. 



From the filled sugar (or urine) burette add about 0-5 c.c. to 

 the warm clear copper solution, boil very gently by moving the test 

 tube to and fro through the flame for two minutes by the watch. 

 If all the copper is reduced, blue colour completely disappears, 

 the urine contains over 5 per cent, sugar and the determination 

 must be repeated with a more dilute solution. If, however, the 

 contents of the test tube are but slightly reduced yielding only 

 a small precipitate of cuprous sulphocyanate, a further amount of 

 sugar solution may be added : boil gently for one minute. Repeat 

 the additions of sugar and the boiling for one minute until complete 

 reduction has taken place. Confirm the result by a repetition, 

 the first addition of sugar solution or urine being only 3 or 4 drops 

 less than the full amount required, boil for three minutes, then 

 add the rest of the urine a drop at a time till complete reduction. 

 Boil for one minute after each addition. The total boiling period 

 for a correct titration must not be less than four nor more than 

 seven minutes. But the preliminary titration may last for eight 

 to nine minutes, and if the boiling process has been gentle the result 

 will be then only about 1 per cent, too high. 



Calculation. 2-5 divided by titration figure in c.c. =per cent, 

 glucose present. 



End point is very sharp with pure dextrose solutions, with urine 

 the end point is the transition from a greenish to a yellow (pale) 

 colour. 



2. Benedict's Method. Dissolve by the aid of heat in about 

 600 c.c. of water, 200 gms. sodium citrate, 100 gms. anhydrous 

 sodium carbonate, and 125 gms. potassium thiocyanate, cool, filter, 

 make up to about 800 c.c. with water. Pour into this solution 

 very carefully and with constant stirring a solution (100 c.c.) con- 

 taining exactly 18 gms. pure copper sulphate (CuS0 4 ,5H 2 0) 

 prepared in a litre flask. Then pour the mixed solution back into 

 the measuring flask (which contained the copper solution) without 

 loss, add 5 c.c. of a 5 per cent, solution of potassium ferrocyanide 

 (to prevent any precipitation of cuprous oxide) and make up the 

 total volume to 1,000 c.c. with the rinsings of the beaker used to 

 mix the two solutions. 



Measure 25 c.c. of the reagent into a 150 c.c. flask or a porcelain 

 basin; add about 4 gms. anhydrous sodium carbonate, heat to 

 boiling and whilst boiling run in the sugar solution (or urine) until 

 the last of the blue colour disappears. The addition of the sugar 

 solution should be at such a rate that the boiling solution is kept 

 nearly constant in volume during the operation. If the urine con- 

 tains a large amount of sugar it should be diluted so that not less 

 than 10 c.c. will be required to reduce the 25 c.c. of reagent employed. 



