SODIUM IN BLOOD 185 



sodium) is added dropwise with shaking until the indicator changes 

 color. The flask is made up to volume, mixed, and the solution 

 transferred to a centrifuge tube. Centrifuging at moderate speed 

 throws down the insoluble phosphates and iron salts. 



Twenty c.c. of the supernatant liquid are pipetted into a 50 

 c.c. Erlenmeyer flask. This solution is evaporated l on the hot 

 plate to 2 to 3 c.c. and rendered just acid with HNOs. An excess 

 of 0.5 c.c. of 2 N HNOa is added and the precipitation carried 

 out as described. 



If deproteinization is preferred to the process of ashing the 

 following will be found helpful. Five c.c. of whole blood or plasma 

 are transferred to a 50 c.c. flask containing 35 c.c. of water, and 5 

 c.c. of trichloroacetic acid (20 per cent) are added. The contents 

 of the flask are diluted to the mark, mixed, allowed to stand about 

 thirty minutes, and filtered through a dry paper. Ten c.c. of 

 filtrate (equivalent to 1 c.c. of blood) are pipetted into a 50 c.c. 

 Erlenmeyer flask and 1 drop of concentrated nitric acid is added. 

 The flask, closed with a trap, is heated on a piece of asbestos on a 

 hot plate until brown fumes from the acid are evolved. It is 

 removed, cooled, and the trap washed off with a few drops of 

 water. Precipitation is then carried out as described below. 



Precipitation. The solution is cooled to 10 to 12 C. and 3 c.c. 

 of reagent are added for each milligram of sodium expected. The 

 flask is stoppered with a two-hole rubber stopper bearing two 

 short glass tubes bent at a right angle. One is fitted with a short 

 rubber tube with a glass plug, the other with a Bunsen valve and 

 plug. Illuminating gas freed from H^S is passed into the flask 

 for a few seconds and the plugs are replaced. The flask is put in 

 the cold room at 1 C. A yellow crystalline precipitate begins to 

 form in a few minutes. Precipitation is complete in twenty-four 

 hours, whereas at room temperature forty-eight hours are required. 

 A scum is much more likely to form before the precipitation is 

 complete at the higher temperature. 



The precipitate is rapidly filtered on a Gooch crucible which 

 has previously been dried and weighed. Washing with the ice- 

 cold 50 per cent acetone which is saturated with sodium cesium 



1 The authors advise the use of a trap in the mouth of the flask to prevent 

 loss by bumping. This is made by blowing a bulb on the closed end of a 

 small soft glass test-tube. A hole is then blown in the side of the bulb which 

 is then cut off from the tube. 



