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QuALiT.\TivE Detection and Separation of Potassium and Sodium. 



F. C. Mathers and I. E. Lee. 



The qualitative detection and separation of potassium and sodium i.s 

 less satisfactory than tests for any other group. Some manuals have 

 abandoned wet methods and use spectrum tests. This is objectionable on 

 account of the great difficulty in testing for potassium in the presence of 

 an excess of sodium and also because the test is so delicate that sodium is 

 detected in almost every chemical substance. 



The test for sodium with potassium pyroantimonate has been unsatis- 

 factory in this laboratory. There are numerous excellent and satisfactory 

 tests for potassium. 



A new method which has been tried in this laboratory and which has 

 been found satisfactory is as follows: Separate the hydrogen sulphide 

 and ammonium sulphide groups by the ordinary methods. Then precipi- 

 tate barium, strontium, and calcium with ammonium carbonate. This 

 leaves, in the solution, magnesium, potassium, sodium, and ammonium 

 salts and perhaps traces of barium, strontium, and calcium, which are 

 sometimes incompletely precipitated by ammonium carbonate. 



Introduce this solution into a small evaporating dish and evaporate to 

 dryness. Ileat (in the hood) over the free gas flame until the ammonium 

 compounds are completely volatilized, i. e., until white fumes are no longer 

 given off. 



Allow the dish to cool, dissolve the residue in about one-fourth of a 

 te.st tube full of distilled water (5-7 cc.) and add 2 to 3 cc. of alcohol (not 

 more than an equal volume of alcohol should be added) and then add a 

 few drops of sulphuric acid^ and filter (I) through a small paper but do 

 not wash. Discard the residue. 



Transfer about one cubic centimeter of filtrate I to a test tube and add 

 one drop of sodium cobaltic nitrate, NagCo (NOo),;. 



A. ]V(! precipitate is formed. Proceed as in B, 2, for the detection of 

 sodium. 



^ The sulphuric acid will remove any liarium, strontium, or calcium which was 

 not precipitated by the ammonium carbonate. 



