POTASSIUM IN BLOOD 191 



only moderate suction was necessary to produce the optimum 

 rate of filtration. Thus, if four crucibles are prepared in the 

 manner described above, over 100 sodium determinations may be 

 made before it is necessary to make a new set. 



Filtration. The precipitate is transferred to the Gooch cru- 

 cible with the aid of a rubber-tipped rod. After the pad has 

 become soaked, moderate suction is used so that the fluid goes 

 through at the rate of 10 to 15 drops per minute. When all the 

 fluid has passed through the filter, the rubber-tipped rod is washed 

 off and the small amount of precipitate remaining in the platinum 

 dish transferred to the Gooch by means of 8 to 12 c.c. of 30 per 

 cent, alcohol. 



Drying. The drying is carried out at 110 C. for one hour and 

 then the crucible and contents are placed in a desiccator to cool. 

 At the end of thirty minutes the crucible is weighed. 



POTASSIUM IN BLOOD 



Method of Clausen 1 



Principle. Blood or plasma is subjected to "wet" washing to 

 remove organic material and the potassium in the clear solution is 

 precipitated as potassium sodium cobaltic nitrite, K2NaCo(NO2)e. 

 2H2O. This precipitate is oxidized in an acid solution with an 

 excess of potassium permanganate and the excess of perman- 

 ganate is titrated with oxalic acid. 



Procedure. The blood is ashed in a 200X25 mm. Pyrex glass 

 tube with a. mixture of nitric and sulfuric acids. For 2 c.c. of 

 plasma, or 1 c.c. of blood, 5 c.c. of a mixture of sulfuric acid, 1 

 part, nitric acid, 20 parts, are sufficient. The tube arranged with 

 a fume absorber as for a Folin micro-Kjeldahl determination is 

 heated by a micro-burner, adjusted so that boiling is slow, for 

 about one-half hour. Foaming and bumping can be largely pre- 

 vented by the Use of a short piece of platinum wire sealed through 

 the bottom of the tube, serving as a heat-conductor and boiling 

 focus. After one-half hour the excess of HNOa is rapidly evapo- 

 rated. The remaining drop of sulfuric acid darkens considerably. 

 At this stage, the flame is turned off, and the small amount of 

 HNOs condensed on the walls of the tube allowed to run back. 

 1 Clausen: Jour. Biol. Chem., 1918, 36, 479. 



