A Procedure for the Qualitative Analysis of the Group: 

 IVIagnesium, Potassium, Sodium. — By Harold S. King, 

 Assistant Professor of Chemistry, Dalhousie University, 

 Halifax, N. S. 



(Read 21 May, 1923) 



The course of qualitative analysis as given at Dalhousie 

 University is so arranged that magnesium is not precipitated 

 with the alkaline earth group but is found associated with the 

 alkali metal group. In this paper a procedure is outlined for 

 the analysis of the last group in the basic analysis, i.e. magne- 

 sium, potassium and sodium. 



The classical method of analyzing for these constituents is 

 to test for magnesium by the phosphate method in a side sam- 

 ple and, if present, to evaporate the solution to dryness and 

 ignite to remove ammonium salts. Then the magnesium is 

 precipitated as hydroxide by means of barium hydroxide, the 

 excess barium is removed as carbonate by the addition of am- 

 monium hydroxide and ammonium carbonate. The solution 

 is evaporated and ignited a second time to remove ammonium 

 salts, and the residue is analyzed for potassium and sodium. 

 The difficulties with this standard procedure are that the barium 

 hydroxide solution absorbs carbon dioxide readily, the filtering 

 and washing of the precipitates are slow, and particularly, two 

 separate evaporations and ignitions are necessary. 



The procedure about to be described is found to be some- 

 what simpler in operation. Its main features are made plain in 

 the accompanying outline, while the detailed description and 

 discussion of the precedure are as follows: 



Procedure 1. Detection of Magnesium. 



Evaporate the filtrate from the alkaline earth group preci- 

 pitation until crystals appear. Add 15 c.c. of ISn.NH^OH 

 and 5-20 c.c. of 4n. H3PO4. A white granular precipitate may 

 be MgNH4P04 and indicates the presence of magnesium. Filter 

 and wash once. Treat the precipitate by P. 2 and the filtrate 

 by P.3. 



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