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812 URINE.
The titration according to Knapp depends on the fact that mercuric
cyanide in alkaline solution is reduced to metallic mercury by glucose. The
titration liquid should contain 10 grams of chemically pure dry mercuric cyanide
and 100 cc. of caustic-soda solution of a specific gravity of 1.145 per liter. When
the titration is performed as described below (according to Worm-Muller and
Otto), 20 cc. of this solution should correspond to exactly 0.05 gram of glucose.
If the process is carried out in other ways, the value of the solution is different.
In this titration also, the quantity of sugar in the urine should be between
\ and 1 per cent, and the extent of dilution necessary be determined by a pre-
liminary test. To determine the end-reaction as described below, the test for the
excess of mercury is made with sulphuretted hydrogen.
In performing the titration allow 20 cc. of Knapp’s solution to flow into a
flask and dilute with SO cc. of water, or when the urine contains less than 0.5
per cent of sugar use only 40-60 cc. After this heat to boiling and allow the diluted
urine to flow gradually into the hot solution, at first 2 cc, then 1 cc, then 0.5 cc,
then 0.2 cc, and lastly 0.1 cc. After each addition let it boil \ minute. When
the end-reaction is approaching, the liquid begins to clarify and the mercury
separates with the phosphates. The end-reaction is determined by taking a
drop of the upper layer of the liquid into a capillary tube and then blowing it out
on pure white filter-paper. The moist spot is first held over a bottle containing
fuming hydrochloric acid and then over strong sulphuretted hydrogen. The
presence of a minimum quantity of mercury salt in the liquid is shown by the
spot becoming yellowish, which is best seen when it is compared with a second
spot that has not been exposed to the gas. The end-reaction is still clearer when
a small part of the liquid is filtered, acidified with acetic acid, and tested with
sulphuretted hydrogen (Otto) 1
. As the added quantity of urine contains 0.050
gram sugar the calculation of the percentage content in sugar, bearing in mind
the extent of dilution, is very simple.
This titration, unlike the previous one, may be performed equally well by
daylight and by artificial light. It is applicable even when the quantity of sugar
in the urine is very small and that of the other urinary constituents is normal. It
is more easily performed, and the titration liquids may be kept without decom-
posing for a long time (Worm-Muller and his pupils 2
) . There is diversity of
opinion, nevertheless, among investigators on the value of this titration method.
Estimation of the Quantity of Sugar by Fermentation. This
may be done in various ways: the simplest method, and one at the same
time sufficiently exact for ordinary cases, is that of Roberts. This
consists in determining the specific gravity of the urine before and after
fermentation. In the fermentation of sugar, carbon dioxide and alcohol
are formed as chief products, and the specific gravity is lowered, partly
on account of the disappearance of the sugar and partly on account of
the production of alcohol. Roberts found that a decrease of 0.001 in
the specific gravity corresponded to 0.23 per cent sugar, and this has been
substantiated since by several other investigators (Worm-Muller and
others). If the urine, for example, has a specific gravity of 1.030 before
fermentation and 1.008 after, then the quantity of sugar contained therein
was 22X0.23 = 5.06 per cent.
In performing this test the specific gravity must be taken at the same
temperature before and after the fermentation. The urine must be
faintly acid, and when necessary it should be acidified with a little hydro-
1
Journal f. prakt. Chem., 26.
2
Pfluger’e Arch., 16 and 23.
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