204 METHODS FOR THE ANALYSIS OF BLOOD 



Calculation. The calculation is very simple when standard 

 solutions of the above concentration are used. The 20 c.c. of 

 filtrate employed for titration represent 0.8 c.c. of plasma, and 

 the unprecipitated portion of the amount of silver nitrate equiva- 

 lent to 8 mgm. of NaCl or 10 mgm. per c.c. of plasma. Each 

 c.c. of KI used in the titration is equivalent to 1 mgm. of NaCl 

 per c.c. of plasma. Hence the calculation simplifies to 



Mg. NaCl per c.c. plasma or ] 



* XT oi IM. f =10.15- c.c. KI. 



Gm. NaCl per liter 



The use of 10.15 instead of 10 c.c. is due to the fact that 0.15 

 c.c. excess of KI solution is required to give the end-point. If the 

 0.15 c.c. of excess iodide required to give the end-point were 

 neglected in the calculation the error would be partially eliminated 

 by neglecting it also in the standardization. It is as simple, how- 

 ever, to allow for it in the calculation and thereby eliminate it 

 entirely. 



Remarks. In the determination of plasma chlorides it is 

 essential that all pipettes, burettes and measuring flasks be accu- 

 rately calibrated since this apparatus as usually obtained from 

 dealers is not sufficiently accurate to be employed for this deter- 

 mination without being checked. 



CHLORIDES IN WHOLE BLOOD OR PLASMA 



Method of Meyers and Short 1 



Principle. Proteins are precipitated from the blood and the 

 chlorides in the filtrate are titrated according to the Volhard 

 method. 



Procedure. Three c.c. of whole blood (or plasma) are added 

 to 27 c.c. of distilled water in a 50 c.c. centrifuge tube. About 

 0.5 gm. of dry picric acid is then added and the mixture stirred 

 until protein precipitation is complete and the whole mixture 

 turns a bright yellow color. The precipitate is now thrown down 

 by centrifuging for a few minutes at moderate speed and the 

 clear supernatant fluid decanted into a clean dry beaker. (If 

 any particles remain suspended the fluid should be filtered.) 



Twenty c.c. are then pipetted into a clean dry 50 c.c. centrifuge 

 tube and 20 c.c. of standard AgNOs solution, of such strength 

 1 Meyers and Short: Jour. Biol. Chem., 1920, 44, 47. 



