38 AN INVESTIGATION OF THE " CHROMATE METHOD" 



Procedure I. Precipitation of group {after ridding of sulphur). 

 To solution after removal of iron and zinc group, (60cc), 

 add lOcc NH4OH, 2OCCNH4CI and 20cc (NH4)2 CO3 at a 

 temperature of 70°, and let stand several minutes. Filter 

 and wash with little cold water. 



j^otes — 1. At temperature much above 70° the carbonates 

 react with the ammonium chloride forming the soluble 

 chloride with evolution of carbon dioxide. 



2. At temperature much lower calcium comes down 

 as a gelatinous mass and barium, also has this tendenc3^ 

 Warming on the water bath will cause them to crystallize. 



3, Precipitation of strontium and calcium is com- 

 plete in 10 minutes and of barium very nearly so. 



Procedure II. Precipitation gf Barium. 



Pour a 5cc portion of acetic acid through the filter a few 

 drops at a time, and pour through repeatedly until it 

 runs through clear. Then wash thoroughly with hot water. 

 Make up to 80cc and heat to boiling. Add 5cc of K2Cr04 

 solution a few drops at a time with constant stirring and 

 boil a few moments. Filter and wash with cold water. 

 (Yellow precipitate shows presence of barium) 



Notes — 1. The 5cc of 50% acid should be diluted somewhat 

 and used hot. 



2. 500 mg. of calcium and strontium fail to pre- 

 cipitate under these conditions while 4 mg. of barium give 

 a distinct test. 



3. The filtrate should be j^ellow rather than red, but 

 should be tested with another drop of chromate. 



Procedure III. Confirmatory test for Barium. 



Pour a little hot HCl through the filter repeatedly and 

 evaporate almost to dryness. Test in flame on platiipium 

 wire. Green color confirms barium. 



