CHLORIDES IN BLOOD 201 



and titrate the excess of silver nitrate with the standard sul- 

 focyanate solution until the definite salmon-red (not yellow) color 

 of the ferric sulfocyanate persists in spite of stirring for at least 

 fifteen seconds. 



(c) Calculation. 5.00 titer (in c.c.) = mg. of Cl per c.c. of 

 blood (or plasma). 



Since each cubic centimeter of thiocyanate solution used is 

 equivalent to 1 c.c. of silver nitrate solution, the difference between 

 the volume of silver nitrate solution taken and the excess deter- 

 mined by the titration, that is 5 titer, represents the volume 

 which reacted with chloride at the ratio of 1 c.c. to 1 mg. of Cl. 

 And the 10 c.c. of filtrate taken represents 1 c.c. of blood (or 

 plasma). 



To convert Cl figures into NaCl figures divide by 0.606. 

 The same result may be more easily obtained by the following 

 rule: To obtain mg. NaCl per 100 c.c., divide mg. Cl per liter by 

 6, and subtract 0.001 of the result. Conversely, to obtain mg. 

 Cl per liter, add to mg. NaCl per 100 c.c. 0.001 of itself and 

 multiply by 6. 



Preparation of Reagents. Silver Nitrate Solution. Dissolve 

 4.791 gms. of c.p. silver nitrate in distilled water. Transfer this 

 solution to a liter volumetric flask and make up to the mark with 

 distilled water. Mix thoroughly and preserve in a brown bottle. 

 One c.c. = 1 mg. Cl. (It is to be noted that the silver nitrate and 

 nitric acid are not added to the protein-free filtrate simultaneously. 

 To do so may result in the mechanical enclosure of silver nitrate 

 solution within the curds, and a consequent error in the positive 

 direction.) 



Because sulfocyanates are hygroscopic, the standard solution 

 should be prepared volumetrically. As an approximation about 

 3 gms. of KCNS or 2.5 gms. of NH 4 CNS should be dissolved in 

 a liter of water. By titration under the conditions specified under 

 " Procedure " and by proper dilution prepare a standard such 

 that 5 c.c. are equivalent to 5 c.c. of the silver nitrate solution. 



The solid ferric alum is used rather than a solution, in order to 

 insure a very high concentration in the mixture to be titrated. 

 It is powdered in order to facilitate its solution. 



