POTASSIUM IN BLOOD 193 



Estimation of Potassium in Pure Solutions 



The reagents are: 



1. Sodium Cobaltic Nitrate Reagent. This is prepared from 

 two stock solutions which keep well several months. 



A. Cobalt nitrate 50 gins. 



Glacial acetic acid 25 c.c. 



Distilled water to 100 c.c. 



B. Sodium nitrite 100 gms. 



Distilled water to 200 c.c. 



Six parts A and 10 parts B are mixed. A rapid current of air 

 is passed through the solution for several hours to remove the 

 fumes of oxides of nitrogen. Then the dark-brown fluid is kept 

 on ice two days. Invariably some yellow precipitate forms, owing 

 to traces of potassium and ammonium in the reagents. The 

 filtered reagent keeps well for several weeks, if in a dark bottle 

 in an ice box. 



2. Potassium Permanganate. This is prepared by diluting 

 0.1 N KMn(>4 to about 0.02 N and boiling under a funnel reflux 

 condenser for two to three hours. After one to two days, the 

 solution is decanted from the manganese oxides which have 

 separated, and preserved in a cool dark place. Such solutions 

 keep well several weeks. 



3. Standard Potassium Solutions. 



A. Standard, 1 c.c. = 10 mg. potassium. 



Pure KC1 9.546 gms. 



HC1 (concentrated) 1 c.c. 



Water to 500 c.c. 



B. Standard, 2 c.c. = l mg. 



Standard A 25 c.c. 



HC1 (concentrated) 1 c.c. 



Water to 500 c.c. 



The potassium chloride is recrystallized several times, then 

 fused. The hydrochloric acid is added to prevent growth cf 

 moulds. 



In conclusion, it is to be emphasized that the reagents must be 

 tested for the presence of potassium. One sample of c.p. NaOH 

 purified by alcohol contained nearly 0.05 per cent potassium. 



