200 METHODS FOR THE ANALYSIS OF BLOOD 



Fe per 100 c.c. of blood should be used (that is 0.005 mg. of Fe 

 per c.c. of standard iron solution). For every 5 mg. above or 

 below the standard of 45 mg. of Fe per 100 c.c., 0.001 mg. is added 

 to or subtracted from the standard of 0.009 mg. of Fe per c.c. 

 Ordinarily, the latter standard, corresponding to 45 mg. of Fe 

 per 100 c.c., is used. 



CHLORIDES IN BLOOD 



Method of Whitehorn, 1 Supplementary to Method of Folin and 

 Wufor Blood Analysis (see this Manual, page 83) 



Principle. Proteins in blood are precipitated by the use 

 of tungstic acid. The chlorides in the filtrate thus prepared are 

 precipitated as silver chloride from a known quantity of silver 

 nitrate and the excess of silver nitrate is determined by titration 

 with sulphocyanate, employing ferric alum as an indicator. 



1. Preparation of Protein-Free Filtrates. The filtrate is pre- 

 pared by the use of the same reagents as have been described in 

 detail by Folin and Wu (see this Manual, page 83) for the deter- 

 mination of non-protein nitrogen, urea, uric acid, creatinine, 

 creatine, and sugar. Because even slight variations in the chlorides 

 are significant, great accuracy is necessary. The author custom- 

 arily uses volumetric flasks in order to insure an accurate 1:10 

 dilution. The method is applicable, without alteration, to either 

 whole blood or plasma. An amount of filtrate equivalent to 1 

 c.c. of blood or plasma is needed. Less may be used but with 

 proportionate loss of accuracy. 



II. Determination of Chloride Content of Filtrate, (a) 

 Reagents Required. 1. Silver Nitrate Solution. (M/85.46). 



2. Potassium (or ammonium) sulfocyanate (M/35.46). 



3. Powdered ferric ammonium sulfate (FeNH 4 ($04)2). 



4. Concentrated nitric acid (HNOz of specific gravity l.J$). 



(6) Procedure. Pipette 10 c.c. of the protein-free filtrate into 

 a porcelain dish. Add with a pipette 5 c.c. of the standard silver 

 nitrate solution and stir thoroughly. Add about 5 c.c. of con- 

 centrated nitric acid, mix, and let stand for five minutes, to permit 

 the flocking out of the silver chloride. Then add with a spatula an 

 abundant amount of ferric ammonium sulfate (about 0.3 gm.) 

 1 Whitehorn: Jour. Biol. Chem., 1921, 45, 449. 



