﻿13. QUALITATIVE SEPAEATION AND DETECTION OF 

 POTASSIUM AND SODIUM WITH PERCHLORIC 

 ACID AND HYDROFLUOSILICIC ACID. 



By Frank C. Mathers, Ph.D., and Ira E. Lee, A.B. 



Introduction. The methods generally employed for the qualita- 

 tive separation and detection of potassium and sodium are time 

 consuming and often inaccurate. Some manuals have abandoned 

 wet methods for spectrum tests. This is objectionable because of 

 the great difficulty of 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 potassium with sodium cobaltic nitrite, Na3Co(N02)6, 

 is entirely satisfactory, although ammonium compounds must be pre- 

 viously removed. This operation is neither difficult nor objectionable. 

 Magnesium does not interfere unless present in very large amounts. 



The potassium pyroantimonate (K-.HoSbiOy) is generally con- 

 sidered the best test for sodium. The results with this method 

 have not been very satisfactory in this laboratory. The tests are 

 never decisive and certain; and, in addition, the previous removal 

 of magnesium is a time consuming operation to be avoided if 

 possible. 



A new method which has been tried in the Indiana University 

 chemical laboratory and which has been found satisfactory is as 

 follows: Separate the hydrogen sulphide, ammonium sulphide, 

 and ammonium carbonate groups by the ordinary methods. This 

 separation 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 the solution into a small evaporating dish, add a few 

 drops of sulphuric acid,i and evaporate to dryness. Heat vigor- 

 ously (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. The sides of the vessel, as well as the bottom, 

 must be heated. 



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

 of a test tube full of distilled water (5 to 7 cc.) and add 2 to 3 cc. 

 of alcohol (the volume of alcohol which is added must not be larger 



1 The sulphuric acid will precipitate any barium, strontium, or calcium which was not removed 

 by the ammonium carbonate treatment. 



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