CHLORIDES IN WHOLE BLOOD 205 



that 1 c.c. is equivalent to 1 mg. of NaCl (Solution 1), and 10 c.c. 

 of the dilute acidified ferric alum indicator added (Solution 2). 

 The contents are stirred to insure thorough mixing and the AgCl 

 precipitate is thrown down in the centrifuge. The clear supernatant 

 fluid is decanted into a clean, dry beaker and 20 c.c. portions are 

 pipetted into each of two small porcelain evaporating dishes for 

 duplicate titrations. 



The titration is made with ammonium thiocyanate solution 

 of such strength that 2 c.c. are equivalent to 1 c.c. of the AgNOs 

 solution (Solution 3). The end-point is definite and consists of 

 the first permanent tinge of reddish brown which extends through- 

 out the mixture. Some experience may be necessary before the 

 end-point is always recognized, but thereafter there need be no 

 difficulty in obtaining exact duplicate titrations. Passing the 

 end-point by one drop will introduce an error ordinarily of about 

 0.5 per cent in estimating chlorides in 100 c.c. of blood or plasma. 



/Titer 5\ 

 Calculation. The calculation is 10 l - X-r)XlOO = mg. 



\ 2 

 of NaCl in 100 c.c. of whole blood or plasma. 



Solutions Required. 1. Silver nitrate of such strength that 

 1 c.c. is equivalent to 1 mg. of sodium chloride, 2.904 gms. to 1000 

 c.c. It may be prepared by a 1 to 10 dilution of the silver nitrate 

 employed in the Volhard-Harvey method for urine. 



2. Acid ferric alum indicator prepared by dissolving 100 gms. 

 of crystalline ferric ammonium sulfate in 100 c.c. of 25 per cent 

 nitric acid and adding four parts of distilled water. This is one- 

 fifth the strength employed for urine. 



3. Ammonium thiocyanate of such strength that 2 c.c. are 

 the equivalent of 1 c.c. of the above silver solution, or one-twen- 

 tieth of the strength employed for urine. It contains approxi- 

 mately 0.65 gm. of the thiocyanate to 1000 c.c. 



To simplify the test further it is possible to combine Solutions 

 1 and 2, two parts of No. 1 and one part of No. 2 being used. 



CHLORIDES IN WHOLE BLOOD 



Method of Austin and Van Slyke l 



Principle. Removal of proteins and titration of the chlorides. 

 Procedure. Take 3 c.c. of blood with 15 c.c. of water in a 

 60 c.c. flask. Add 30 c.c. of saturated picric acid solution and 

 1 Austin and Van Slyke: Jour, Biol. Chem., 1920, 41, 345. 



