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Qualitative Detection and Separation of Potassium and Sodium. 



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



The quiilitative detectimi ;uh1 separjitidU of potassium and sodium is 

 less satisfactory tlian tests for any otlier group. Some manuals have 

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

 account of the great difhculty 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 lal)oratory. 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 preciintated by annnonium carbonate. 



Introduce this solution into a small evaporating dish and evaporate to 

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

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

 given off. 



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

 test tube full of distilled water (H-T cc.) and (uUl 2 to 3 cc. of alcohol (not 

 )))orr tlidti an equal rohnnc 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 tulve and add 

 one drop of sodium c*obaltic nitrate, NasCo (No,),.. 



A. No precipitate is formed. I*roceed as in B, 2, for the detection of 

 sodium. 



' The sulphuric acid will romove any barium, strontium, or calcium which was 

 not prpcipitated Ity the ammonium carbonate. 



