186 METHODS FOR THE ANALYSIS OF BLOOD
bismuth nitrite is quickly carried out. Speed during the filtration and washing is essential for good results. Ten c.c. of the 50 per cent acetone are used; 2 c.c are blown from a miniature wash bottle (made from a 10 c.c. graduated cylinder) into the precipitation flask. The suction is stoppered and the liquid poured onto the mat. This is repeated four times. Ten c.c. of pure acetone are used to complete the transfer of the precipitate to the Gooch. If the volumetric or colorimetric procedure is used, complete transference of the precipitate is not necessary.
The Gooch is dried in an air bath at 100° C. until a constant weight is obtained.
Weight of precipitate X0.03675 = Weight of sodium in solution.
Volumetric Procedure.—The Gooch crucible and contents are placed in a tall 200 c.c. beaker. A large excess of standard permanganate (at least twice the amount necessary for oxidation) and enough water to cover the crucible are added. The precipitate is stirred loose from the crucible and asbestos. Ten c.c. of 1:1 sulfuric acid are poured in while the liquid is being stirred. After a few minutes the solution is heated to 75°C., an excess of standard oxalic acid added, and the titration finished with permanganate. A blank must be run on the reagents under similar conditions.
C.c. KMnO4Xnormal factorX8 = Mg. O used
Mg. OX7.82 = Mg. precipitate
Mg. precipitateX0.03675 = Mg. sodium.
Colorimetric Procedure.—For those who prefer a colorimetric method a suitable technique follows. The precipitate is completely transferred to a beaker and 10 c.c. of the alkaline tartrate are added. Upon warming, the salt rapidly dissolves. The solution is quantitatively transferred to a 100 c.c. volumetric flask, cooled, made up to volume, and mixed. A further dilution is made so that a volume containing approximately 0.01 mg. of N can be taken for colorimetric comparison.
The standard and unknown in 100 c.c. volumetric flasks are diluted to about 90 c.c. Two c.c. of the sulfanilic acid and naph-thylamine solutions are added to each. The flasks are made up to volume, mixed, and allowed to stand twenty minutes for the full color development. There is a very wide range of propor-