URINE 525 



a piece of tight fitting rubber tubing sufficiently long (about 2 inches), so that it 

 may be provided with a pinch cock or clamp to shut off the contents of the flask 

 from the outside air (see Fig. 81, page 281). 



Introduce into the flask o.i to 2.0 c.c. (or more) of the sugar solution contain- 

 ing not more than 10 mg. of glucose. Then add 55 c.c. of the diluted copper 

 solution. 1 Heat over an asbestos gauze with a flame standardized to bring the 

 solution to the boiling-point in from 3 1/2-3 3/4 minutes. Boil for exactly 3 

 minutes, being prepared to close the flask with the pinch-cock at the end of the 

 3 minutes. Remove from the flame and at once cool under the tap to room tem- 

 perature. Remove the rubber tubing, add to the contents of the flask 1/2-1 

 c.c. of the starch solution (i gram of soluble starch in 100 c.c. of saturated KC1 

 solution, which keeps indefinitely). Titrate with the standard iodine solution 1 

 run in from an accurate burette with a glass stopcock. When the iodine starch 

 color appears throughout the solution rotate gently and let stand a few seconds. 

 The end point is reached when the blue color endures for 10-20 seconds. It is 

 preferable to carry out the titration in an atmosphere of carbon dioxide, main- 

 tained by means of a delivery tube hung over the side of the flask. Otherwise 

 the titration must be carried out rapidly to prevent reoxidation by the oxygen of 

 the air. 



Calculation. Divide the number of cubic centimeters of N/ioo iodine solu- 

 tion used in the titration by 2.7 to obtain the number of milligrams of glucose in 

 the amount of solution used. 



This method is suitable for urine analysis. The urine must however be free 

 from albumin and as urine contains substances reacting slowly with iodine the 

 end point must be taken when the blue color persists for about 10 seconds and any 

 slow decolorization disregarded. 



Interpretation. See page 523. 



4. Peters' Method. 2 Principle. The sugar solution is boiled with an alkaline 

 copper solution under rigidly standardized conditions and after nitration the un- 

 reduced copper is determined by adding potassium iodide and titrating the liber- 

 ated iodine with standard thiosulphate solution. 



Procedure. A . The Heating Power. It is necessary to standardize the heating 

 power of the flame used in the reduction process. A 200 c.c. Erlenmeyer flask of 

 Jena glass and of about 6 cm. basal diameter is used. This bears a two-hole rubber 

 stopper, one hole of which carries a thermometer. The lower end of the thermome- 



1 Copper solution. Stock Solution. Dissolve first 160 grams potassium bicarbonate, 

 100 grams potassium carbonate and 66 grams of potassium chloride with about 700 c.c. 

 of distilled water in a liter flask. Pure salts must be used in each case. As the bicarbonate 

 is difficulty soluble it should be finely powdered and brought into solution first, preferably 

 with warming to 3OC. The KC1 is then dissolved and finally, with cooling, the carbonate. 

 Then add 100 c.c. of a 4.4 per cent solution of pure crystalline CuSO 4 .5H 2 O. Fill to the 

 mark with distilled water. Mix without strong shaking and let stand for 24 hours before 

 using. 



Dilute Copper Solution. Dilute 300 c.c. of the stock solution to 1000 c.c. Mix with 

 only gentle shaking. Allow to stand for several hours before using. 



Standard Iodine Solution. The N/ioo iodine solution is made. by dilution of N/io 

 iodine solution (see appendix) with boiled out distilled water. The solution is stable for 

 three months if kept in a dark bottle. It may also be prepared daily from KI and KIOs. 

 Introduce into a 100 c.c. flask about i c.c. of 2 per cent KIOs, and2-2.5 grams of KI and 

 then exactly 10 c.c. of N/io HC1. The HC1 liberates an equivalent amount of iodine (sul- 

 phuric acid is less desirable). Make to 100 c.c. with distilled water and mix. 



2 Peters: /. Am. Chem. Soc., 34, 928, 1912; 34, 422, 1912. 



