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760 URINE.
The silver-nitrate solution may be a N/10 one. It is often made of
such a strength that each cubic centimeter corresponds to 0.006 gram
CI or 0.01 gram NaCl. This last-mentioned solution contains 29.075
grams of AgXC>3 in 1 liter.
Freund and Toepfer, as well as Bodtker,1
have suggested modifica-
tions of Mohr’s method.
Volhard’s Method. Instead of the preceding determination, Vol-
hard’s method, which can be performed directly on the urine, may be
employed. The principle is as follows: All the chlorine from the urine
acidified with nitric acid is precipitated by an excess of silver nitrate,
filtered, and in a measured part of the filtrate the quantity of silver added
in excess is determined by means of a sulphocyanide solution. This
excess of silver is completely precipitated by the sulphocyanide, and a
solution of some ferric salt, which, as is well known, gives a blood-red
reaction with the smallest quantity of sulphocyanide, is used as an indicator.
We require the following solutions for this titration: 1. A silver-
nitrate solution which contains 29.075 grams of AgNOs per liter, and of
which each cubic centimeter corresponds to 0.01 gram NaCl or 0.00607
gram CI. 2. A saturated solution at the ordinary temperature of chlorine-
free iron alum or ferric sulphate. 3. Chlorine-free nitric acid of a specific
gravity of 1.2. 4. A potassium-sulphocyanide solution which contains
8.3 grams KCNS per liter, and of which 2 cc. corresponds to 1 cc. of the
silver-nitrate solution.
About 9 grams of potassium sulphocyanide are dissolved in water and diluted
to 1 liter. The quantity of KCNS contained in this solution is determined by the
silver-nitrate solution in the following way: Measure exactly 10 cc. of the silver
solution and treat it with 5 cc. of nitric acid and 1-2 cc. of the ferric-salt solu-
tion and dilute with water to about 100 cc. Now the sulphocyanide solution
is added from a burette, constantly stirring until a permanent faint-red colora-
tion of the liquid takes place. The quantity of sulphocyanide found in the solu-
tion by this means indicates how much it must be diluted to be of the proper
strength. Titrate once mere with 10 cc. of AgNOs solution and correct the sul-
phocyanide solution by the careful addition of water until 20 cc. exactly cor-
responds to 10 cc. of the silver solution.
The determination of the chlorine in the urine is performed by this
method in the following way: Exactly 10 cc. of the urine are placed in a
flask which has a mark corresponding to 100 cc. and which is provided
with a stopper; 5 cc. of nitric acid are added; dilute with about 50 cc.
of water and then allow exactly 20 cc. of the silver-nitrate solution to
flow in. Close the flask with the stopper and shake well, remove the stop-
per and wash it with distilled water into the flask, and fill the flask to the
100-cc. mark with distilled water. Close again with the stopper, care-
fully mix by shaking, and filter through a dry filter. Measure off 50
cc. of the filtrate by means of a dry pipette, add 3 cc. of ferric-salt solu-
tion, and allow the sulphocyanide solution to flow in until the liquid
above the precipitate has a permanent red color. The calculation is
very simple. For example, if 4.6 cc. of the sulphocyanide solution
x
Freund and Toepfer, see Maly’s Jahresber., 22; Bodtker, Zeitschr. f. physiol.
Chem., 20.
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