Preparation of Pure Alkali Nitrites. 



By 



Edward Divers, M. D., D. Sc, F. R. S., Prof., 

 Imperial University, Tokyo. 



When ♦ pure sodium or potassium nitrite is wanted, it is 

 customary to prepare silver nitrite from crude alkali nitrite, and 

 convert this again into alkali nitrite by means of sodium or 

 potassium chloride. The crude nitrite must be nearly free from 

 sulphate and, either before or after adding the silver nitrate to 

 it, nitric acid must be added till all hydroxide and carbonate 

 are neutralised. The silver nitrite is got in the most conveni- 

 ent form for washing by precipitating it from concentrated 

 solutions. Silver chloride is very sensibly soluble in a concen- 

 trated solution of alkali nitrite, and when the solution is no 

 longer clouded by the addition of more alkali chloride, it al- 

 ready contains this salt in excess. Therefore, somewhat large 

 dilution is necessary and this entails, of course, much evapora- 

 tion afterwards. 



The silver nitrite process is evidently not a very satisfactory 

 one, and when sodium nitrite is wanted pure, it is better to 

 recrystallise, three times over, the commercial 96 per cent, 

 sodium nitrite, well draining each time on the suction funnel. 

 A concentrated solution of the crude salt should be left to clear 

 from lead-turbidity for two days or be fdtered cold through a 

 fine filter. The lead carbonate is more soluble in the hot 

 nitrite solution than in the cold. After sej)arating the lead, 



