The Determination of Sodium in Blood.*

A knowledge of the amount,s of sodium salts in tissues and biological fluids is of considerable importance in reaching an understanding of the physiological r61e of inorganic substances. However, an adequate study of the variations in the amount of sodium in blood, for instance, under different physiological and pathological conditions would be difficult if not impossible by methods1 now in use. The quantitative determination of sodium by exist2 ing methods requires the ashing of the material, the removal of sulfates, phosphates, iron, calcium, and magnesium, and the estimation of potassium in the weighed alkali chlorides. Such a long and tedious procedure seriously limits a study of the metabolism of sodium. Another limiting factor is the amount of material necessary for an analysis, at least 15 cc. of blood being required for the usual gravimetric method. These considerations prompted the search for a shorter method for the determination of sodium in smaller amounts of material. It seemed essential that some insoluble compound of sodium be found which would permit its quantitative precipitation. The most promising of the very few sodium compounds having small solubility appeared to be the complex sodium cesium bismuth nitrite described by Ball (2) and used by him for sodium determinations. A method based upon the precipitation of this