POTASSIUM IN BLOOD 195 



dish is then removed, allowed to cool, and the ash dissolved in 

 0.5 c.c. of water with the aid of one or two drops of glacial acetic 

 acid. 0.5 to 1 c.c. of sodium cobalti-nitrite reagent is then added, 

 drop by drop, with stirring and the mixture allowed to stand for 

 at least ten minutes. During this time a Gooch crucible is prepared. 

 One or two pieces of hardened filter paper are placed at the bottom 

 then asbestos emulsion is poured in, and the pad sucked dry. 

 When finished the pad should be at least 2 mm. in thickness and 

 should be washed with a large quantity of water. 'The precipitate 

 is transferred to the wet pad. The suction should be regulated 

 so that the water runs through drop by drop; the rest of the 

 precipitate is washed onto the pad with small portions of cold 

 water. It is then washed repeatedly with small portions of water 

 until the washings return perfectly clear. Precipitate and pad are 

 then transferred en masse to a 50 c.c. beaker, and the crucible is 

 washed with a little water. 1 The paper is then removed with a 

 forceps and washed clean with distilled water. Not more than 10 

 c.c. of water need be used for complete transference of asbestos 

 pad and precipitate. Twenty-five c.c. (an excess) of 0.01 N 

 potassium permanganate and 5 c.c. of 25 per cent sulfuric acid 

 are added. The mixture is stirred, heated over the steam bath 

 for just three minutes, and sufficient 0.01 N oxalic acid is then 

 added to decolorize the solution completely. The material is at 

 once titrated back to a permanent pink with 0.01 N KMnO4 

 solution. The total number of c.c. of 0.01 N KMnCU number 

 of c.c. of 0.01 N oxalic acid X 0.071 = mg. of potassium in the sample. 

 ( A blank may be done but the correction is insignificant as a 

 rule. 



Preparation of the Reagents. 25 per cent sulfuric acid is 

 made by diluting chemically pure concentrated sulfuric acid with 

 water. It should be tested with permanganate for the presence 

 of organic matter. 



Solution A. Fifty gms. of cobalt nitrate crystals (J. T. Baker) 

 are dissolved in 100 c.c. of water and to this solution 25 c.c. of 

 glacial acetic acid are added. 



bath, then dried in the incubator at 105 C., and heated until a white crys- 

 talline ash is obtained. 



1 The pad need not be sucked dry. By means of a glass rod it may be 

 dislodged by a half turn and can then be transferred as a whole including 

 the entire precipitate. 



