SODIUM IN BLOOD 187 







tionality of color intensity to the amount of nitrite present. The 

 colors are very stable. 



The calculation is simple. 



20X0.01 AT . 



= mg. N in sample used 



Unknown reading 

 Suppose the sample was 1 c.c. of a dilution of 1:1,000 then 

 Mg. N in sample XI, 000 = mg. N in precipitate 



9CsNO 2 .6NaN02.5Bi(NO 2 )3 _ 3753.6 _ Q QQ 

 ~30~N~ "4203"' 



Mg. NX8.93 = mg. precipitate 



Mg. precipitate X 0.0367 = mg. sodium in sample 



The authors prefer the volumetric method to either the gravi- 

 metric or colorimetric on account of its greater speed and accuracy. 

 Possible contamination of the precipitate with either bismuth 

 subnitrate or potassium nitrate renders the gravimetric values 

 doubtful. The colorimetric procedure is open to the usual errors 

 of such methods. The red color is very bright and comparison is 

 rather difficult. 



Reagents 



1. Bismuth Cesium Nitrite Solution. 30 gms. of sodium- 

 free potassium nitrite 1 are dissolved in about 60 c.c. of pure 



1 Pure potassium nitrite has been a source of considerable difficulty which 

 has finally been overcome. The potassium salts on the market generally 

 certain large quantities of sodium. Since the nitrite cannot be purified 

 by recrystallization, the only recourse is to make it. Various samples of 

 carbonate have been examined and it has been found that both Merck's 

 Blue Label and Eastman's are substantially free from sodium. As an emer- 

 gency procedure sodium-free potassium carbonate may be made by recrys- 

 tallization of the oxalate. It is dried and ignited in a platinum dish. 



The pure nitrite is made by passing nitrous fumes into a 25 per cent solu- 

 tion of sodium-free potassium carbonate. Nitric acid (sp. gr. 1.2) is dropped 

 from a separatory funnel into a flask containing arsenious oxide. A delivery 

 tube carries the fumes into the carbonate. The reaction is complete when 

 the solution in the receiving flask gives off many fine bubbles of carbon 

 dioxide on shaking. Nitrite determinations are run at intervals to ascertain 

 whether the reaction is running perfectly. 



