ESTIMATION OF SUGAR IN URINE. 811 



are removed. If an acidified urine is used for the titration then the urine 

 is added to the copper solution and not the reverse. 



BANG'S Second Method. As the reagents necessary for the preceding titration 

 are expensive, and as the copper solution only keeps for three months, and the 

 preparation of the solutions requires great exactitude and is somewhat difficult, 

 and as the method gives somewhat higher results than other reduction methods 

 due to the high alkali and salt content of the solutions, BANG l has recently 

 modified his original method. Instead of potassium thiocyanate he uses potassium 

 chloride, which can also keep the cuprous oxide in solution as a colorless com- 

 pound. Also the non-reduced cupric oxide remaining, as in the early method, is not 

 determined, but the cuprous oxide formed in the reduction with the sugar is directly 

 determined by titration. This is done by means of a N/100 (or N/10 or N/25) 

 iodine solution, which in the alkaline liquid acts oxidizingly with the formation 

 of cupric oxide, according to the formula: CuCl+I+K 2 CO 3 =CuC0 3 +KCl+KL 

 Starch solution is used as indicator. As the potassium chloride can only hold 

 small amounts of cuprous oxide in solution, and as the end-reaction with the blue 

 iodine-starch cannot be determined with ease in the presence of large amounts 

 of cupric oxide in solution, but can easily be done with the faintly blue coloration 

 due to cupric oxide, by this method a maximum of 10 milligrams sugar can only be 

 determined. On this account a urine rich in sugar must be diluted considerably 

 before titration. It must also be remarked that the iodine does not only react 

 with the cuprous oxide but also with other urinary constituents, and the importance 

 of this method on titration with rich urines, poor in sugar, has not been sufficiently 

 investigated. This method has given good results with pure sugar solutions and 

 with blood; but as its use for the determination of sugar in the urine has not 

 been sufficiently tested, we have only given the chief points of the method. 



BERTRAND'S 2 Titration Method is more complicated than BANG'S method and 

 does not seem to have any special advantages over this latter, at least in regard 

 to the determination of sugar in the urine. A part of the cuprous oxide here also 

 remains in solution and like the titration, according to FEHLING, the cuprous 

 oxide sometimes settles only with difficulty. As this method seems to be used 

 extensively we will give the principles of the method. 



The method consists in boiling the sugar solution (sugar urine) with an excess 

 of FEHLING'S solution. The cuprous oxide, freed from copper salt by decantation 

 and washing (under special precautions), is dissolved by ferric sulphate in sulphuric 

 acid, and the ferrous sulphate produced is determined by titration with potassium 

 permanganate, standardized by oxalic acid. The equations of the reactions are 

 as follows: 



1. Cu 2 0+Fe 2 (S0 4 ) 3 +H 2 S0 4 = H 2 0+2CuS0 4 +2FeS0 4 



2. 10FeS0 4 +2KMn0 4 +8H 2 S0 4 = 8H 2 0+5Fe 2 (S0 4 ) 3 + 2MnS0 4 +K 2 S0 4 . 



2 Cu are equivalent to 2 Fe, and as these are equivalent to 1 mol. oxalic acid, 

 then from the amount of oxalic acid (ammonium oxalate) used in the standardiza- 

 tion of the potassium permanganate solution the quantity of copper separated as 

 cuprous oxide can be readily calculated. The corresponding quantity of sugar 

 may be found in a special table. 



For exact determinations of sugar the method as suggested 'by ALLIHN 

 and modified by PFLUGER 3 is the best suited. 



1 Bioch. Zeitschr., 49. 



a Bulletin de la Soc. chim., (3), 35, (1906). 



Pfluger's Arch., 66. 



