16 PKEPAEATION OF PUKE ALKALI NITRITES ; 



the solution should be fully neutralised with nitric acid, before 

 evaporation for crystallising. Potassium nitrite is too soluble 

 and deliquescent to be conveniently purified in a similar way. 



A most satisfactory and simple process for preparing either 

 sodium or potassium nitrite, when the pure hydroxide or car- 

 bonate is at command, is to saturate this with red fumes under 

 appropriate conditions. That nitrites can be thus obtained is 

 known to every chemist, was known to Gay-Lussac in 1816, 

 and was described by Fritzsche in 1840, but it has hitherto 

 been stated and believed that much nitrate is then unavoidably 

 formed along with the nitrite. That is a mistake, and therefore 

 this note is published. If obvious precautions of the simplest 

 kind are taken, so little nitrate, if any, is formed, as to be hardly 

 detectable with certainty in presence of so much nitrite. Con- 

 sequently, if the quantity of pure alkali taken is known, a 

 solution of given strength in nitrite is perhaps better prepared 

 in this way than in any other. 



Avoiding so far as practicable, the use of cork and caout- 

 chouc, nitrous gases, from nitric acid and starch or arsenious 

 oxide, are passed into the concentrated solution of the hydroxide 

 or carbonate until the alkali is quite neutralised. Sodium carbo- 

 nate alone is somewhat inconvenient, because of its sparing 

 solubility, but this may be circumvented by adding it, finely 

 divided and in sufficient quantity, to its own saturated solution 

 just before passing the gases, and by often shaking the vessel 

 during their absorption. To prevent free access of air, the 

 nitrite is prepared in a flask with its mouth kept loosely closed, 

 while the gases are passing. Cooling the flask is not necessary. 

 The strength of the nitric acid and the temperature of the 

 generation of the nitrous gases must be so regulated that just 



