CH. xiir .] GLUCOSE. 345 



page 127 is of great service when a large number of diabetic urines have to be 

 examined. The results may be rather low owing to the presence of the laevo- 

 rotatory /3-oxy-butyric acid. 



The method described below is the only one at present available for the 

 estimation of such small amounts of glucose as are present in normal urine. 

 It is included in the hope that the study of slight variations from the normal 

 will extend our knowledge of the pathology of diabetes, and also as a practical 

 method for the detection of lowered tolerance to carbohydrates. 



407. The estimation of glucose in normal urine (Benedict and 

 Osterberg).* 



Principle. The urine is treated with mercuric nitrate and neutralised 

 with sodium bicarbonate. The creatinine, urates, etc., are thus removed. 

 The mercury is removed by means of zinc and the sugar estimated by the 

 colorimetric method with picric acid. 



Solutions and apparatus required.^ 



1. Picric-pier ate mixture, see p. 251. 



2. Standard solution of glucose. The stock solution is described on 

 p. 251. 5 cc. of this are diluted to make 50 cc. with distilled water, i cc. 

 contains i mg. glucose. 



An alternative standard can be prepared from pure picramic acid. The 

 stock solution is described on p. 251. 105 cc. of this are treated with 0-5 cc. 

 of 20 per cent, sodium carbonate and 15 cc. of the picric-picrate mixture and 

 diluted to make 300 cc. with distilled water. The colour obtained corresponds 

 to that of i mg. glucose in 4 cc. of water, treated as described for the final urine 

 filtrates and the coloured solution diluted to 25 cc. It is the most convenient 

 standard to use, as time is saved and a possible error of measurement avoided. 



3. Sodium carbonate solution, 20 per cent., see p. 252. 



4. Test-tubes graduated at 12-5 and 25 cc., see p. 252. 



5. Ostwald pipettes, see p. 381. 



6. A colorimeter, see p. 384. 



7. Mercuric nitrate solution, see A solution, p. 391. On no account must 

 the B solution be used as a substitute. 



Method. Into a 50 cc. beaker measure 20 cc. of the urine and 

 then 20 cc. of the mercuric nitrate solution. Mix and add solid 

 sodium bicarbonate with gentle shaking. Considerable frothing 

 occurs. The bicarbonate can be added fairly freely until this 

 ceases. Stir well and see that the material on the sides of the 

 beaker is mixed with the main mass, which forms a kind of paste. 

 Now add the bicarbonate until the fluid reacts just alkaline to 

 litmus paper. Filter at once through a dry paper into a small dry 



* Journ. Biol. Chem., xxxiv., p. 195. 



| These can be obtained from Messrs. Baird and Tatlock, London. 



