MICROCHEMICAL METHODS FOR BLOOD ANALYSIS 309 



cause the greater part of the blue color is formed in the bulb of 

 the tube. Make the reading in a Colorimeter as usual. 



Method for the Determination of Chlorids in Blood Plasma. 

 (Rappleye: Jour. Biol. Chem., 1918, xxxii, 509). In this 

 method the principle used in the Volhard Method for the deter- 

 mination of chlorids in urine is employed for the estimation 

 of the minute amounts of sodium chlorid found in blood plasma. 



The following solutions are required : 



SOLUTION I 



Silver Nitrate, 7.2653 gms. 



Nitric Acid (concentrated), 250 c.c. 



Saturated Solution of Iron- Ammonium- Alum, 50 c.c, 



Distilled water to make 1000 c.c. 



SOLUTION II 



Potassium sulphocyanate in distilled water of such strength 

 that 25 c.c. is exactly equivalent to 5 c.c. of the silver nitrate 

 solution. Each c.c. of the silver nitrate solution is exactly 

 equivalent to 2.5 mg. of sodium chlorid and each c.c. of the 

 potassium sulphocyanate is equivalent to 0.5 mg. of sodium 

 chlorid. 



PROCEDURE 



Place 2 c.c. of citrated plasma (oxalated plasma cannot be 

 used on account of the poor end point) in a 50 c.c. volumetric 

 flask containing 30 c.c. distilled water. Add 10 c.c. of Solution 



I and make to mark. After being mixed the liquid is allowed 

 to stand for 5 to 10 minutes and is then filtered through a dry 

 filter paper free from chlorids. Twenty-five c.c. of the filtrate 

 is then titrated with Solution II. 



To calculate the result subtract the number of c.c. of Solution 



II used in the titration from 25 and multiply by 50. This gives 

 the number of milligrams of sodium chlorid present in 100 c.c. 

 of blood plasma. 



