196 METHODS FOR THE ANALYSIS OF BLOOD 



Solution B. Fifty gms. of c.p. sodium nitrite (potassium-free) 

 (J. T. Baker) are dissolved in 100 c.c. of water. Mix six volumes 

 of Solution A and ten volumes of Solution B. An evolution of 

 nitric oxide gas occurs at once. Air is drawn through the solution 

 until all the gas has passed off. The reagent is then allowed to 

 stand in the ice box for at least twenty-four hours. It is best 

 filtered before using. 



The cobalt nitrate and sodium nitrite need be w r eighed only 

 roughly. If kept in the ice box the reagent will keep for at least 

 a month and often much longer. Although 1.5 c.c. of reagent 

 will precipitate as much as 20 mg. of potassium it is best to use 

 about 0.5 c.c. where 1 mg. of potassium or less is thought to be 

 present. For quantities between 1 to 3 mg. 1 c.c. of reagent will 

 suffice. 



0.01 N Potassium Permanganate Solution. 0.01 N potassium 

 permanganate solution is prepared from a N or 0.1 N solution by 

 appropriate dilution. The solution is standardized against a 

 known 0.01 N oxalic acid solution. The latter is made from a N 

 oxalic acid solution. 



Na, Ca, Mg, Fe, sulfates, chlorides, and nitrate do not inter- 

 fere. Ammonia must be removed. Although such small amounts 

 of phosphates as occur in normal blood do not interfere with the 

 accuracy of the potassium determination, nevertheless, as has 

 recently been shown, the inorganic phosphates may be markedly 

 increased in the blood serum in certain pathological conditions. 

 Hence it may be necessary to remove them. The following 

 method has been found satisfactory. The solution of blood or 

 serum ash acidified with hydrochloric acid is heated on the steam 

 bath for a few minutes. Two c.o. of 2 per cent BaCk solution 

 are added drop by drop followed after a few minutes by 0.5 c.c. 

 of concentrated ammonia. Fifteen c.c. of a saturated solution of 

 ammonium carbonate in a mixture of equal volumes of concentrated 

 ammonia and 95 per cent alcohol are added drop by drop with 

 stirring. After one-half hour the precipitate, which contains 

 practically all the barium, calcium, magnesium, sulfate, and 

 phosphate, is filtered through ash-free filter paper and washed 

 several times with the precipitating reagent. 



When the filtrate which contains the sodium and potassium 

 has been evaporated to a small volume, a few drops of concentrated 

 hydrochloric acid are added. Evaporation to dryness is continued 



