184 METHODS FOR THE ANALYSIS OF BLOOD 



with a reagent that has been kept in the ice box for two months, 

 nevertheless, it is always best to prepare the solution fresh each 

 time. The potassium antimonate need be weighed only roughly 

 and the rest of the preparation takes but a few minutes. 10 per 

 cent KOH should preferably be free of both sodium and ammonium 

 salts. Alcohol-washed KOH contains relatively little of these. 

 The exact content, if any is present, should, of course, be deter- 

 mined and a correction made for the amount used. This solution 

 should also be made fresh or kept so that it will neither absorb 

 ammonia nor dissolve sodium. 



SODIUM IN BLOOD 



Method of Doisy and Bell * 



Principle. Blood is either ashed (wet) or freed from protein 

 by precipitation. The sodium in the resulting solution is pre- 

 cipitated as sodium cesium nitrite. The sodium may be estimated 

 gravimetrically, volumetricalry or colorimetrically. 



Procedure. 1 c.c. of whole blood, plasma, or urine is trans- 

 ferred to a pointed Pyrex tube. 2 A few drops of HaSC^ (concen- 

 trated) and 5 c.c. of HNOs (concentrated) are added. A low 

 flame which keeps the liquid boiling gently is used. The digestion 

 is continued in the usual manner until the liquid is colorless. 

 Urine is completely oxidized in about eight minutes but the blood 

 generally takes three-quarters of an hour. 



As both iron salts and any appreciable amount of phosphates 

 interfere with this method of determination of sodium, they must 

 be removed from the blood digest. ' 



The digest of the whole blood is quantitatively transferred to 

 a 25 c.c. volumetric flask with about 20 c.c. of water. One drop of 

 methyl orange and 5 to 6 drops of 4 per cent bismuth nitrate are 

 added. A strong solution of potassium carbonate (free from 



1 Doisy and Bell: Jour. Biol. Chem., 1921, 45, 313. 



2 These tubes are reclaimed from non-protein nitrogen determinations. 

 After a tube has been rendered unserviceable by the phosphoric acid it is 

 heated in an oxygen-gas flame and drawn out to a point. The tubes with 

 small tips and thin walls stand heating best. The pointed tip provides a 

 constant stream of bubbles which promote even boiling. No boiling stones 

 are necessary. 



