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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 «
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 X/25)
iodine solution, which in the alkaline liquid acts oxidizinidy with the formation
of cupric oxide, according to the formula: CuCl-f-I+K2 C03 =CuC03 -(-KC*l-(-KI.
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 clone 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. Cu2 0+Fe2 (S04 ) 3 +H2 S04 = H2 0-r-2CuS04 +2FeS04
2. 10FeSO4 +2KMnO4 +8H2SO4 =8H20+5Fe2 (S04 )3+2MnS04 +K2S04 .
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.
1
Bulletin de la Soc. chim., (3), 35, (1906).
1
Pfluger’s Arch., 66.
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