PRACTICE XXII (CONTINUED) 



6. Total Potassium. 



Fuse 1 g. of soil with 1 g. of ammonium chlorid and 8 g. of cal- 

 cium carbonate in a platinum crucible 1 according to the method of 

 J. Lawrence Smith. 2 Transfer the fused mass to a porcelain dish, 

 slack with hot water, grind finely with an agate pestle, transfer to a 

 filter, and wash with about 400 cc. of hot water. Concentrate the 

 filtrate and washings in a Jena-glass beaker to 10 or 20 cc. on the 

 water bath, filter, and wash. Acidify filtrate and washings with 

 hydrochloric acid, concentrate to about 10 cc., and add 1.5 cc. of 

 a platinic chlorid solution, of which 10 cc. contains 1 g. platinum. 

 Evaporate on the water bath to a sirupy consistency, cool, take up 

 with about 10 cc. of 80 per cent alcohol, filter, wash ten or twelve 

 times with 80 per cent alcohol, three times with a solution of ammo- 

 nium chlorid (200 g. ammonium chlorid in 1000 cc. of water satu- 

 rated with potassium platinic chlorid), and again ten times with 80 

 per cent alcohol. Allow the filter to dry thoroughly, and dissolve 

 the potassium platinic chlorid in hot water, catching the solution and 

 washings in a weighed porcelain or platinum dish. Evaporate to 

 dryness on the water bath, heat thirty minutes at 110 in an air 

 bath, cool in a desiccator, and weigh. 



Weight of dish + K 2 PtCl 6 



Weight of dish 



Weight of K 2 PtCl 6 



Weight of K 



Per cent of K 



Av. per cent 



K in 2 million of soil 



1 The fusion may be made in the iron crucible used for the phosphorus determina- 

 tion. Because of the high temperature necessary, however, but four or five deter- 

 minations can be made in the one crucible. 



2 Fresenius's " Quantitative Chemical Analysis," 190i, p. 1175. 



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