METHODS OF ANALYSIS. 31 



and the paper and contents beaten into a pulp. The yellow precipi- 

 tate is then dissplved by the addition of a small amount of standard 

 potassium hydroxid solution (1 cc = 1 mg of P 2 O 5 ); phenolphthalein 

 is added and the solution titrated with standard nitric acid solution of 

 exactly the same strength as the alkaline solution. From the data so 

 obtained the phosphoric acid ions in the water can be calculated in 

 parts per million. a 



BARIUM AND STRONTIUM. & 



The washed residue remaining after evaporating a large quantity of 

 the water with sodium carbonate and filtering is used for this deter- 

 mination. The filter and contents are dried and the contents trans- 

 ferred to a large platinum dish, the filter burned, and the ash added 

 to the same platinum dish. The residue thus obtained is treated twice 

 with sulphuric and hydrofluoric acid to get rid of silica, and the excess 

 of these substances is driven off each time by heating with the full 

 flame of a Bunsen burner. The residue is then fused with sodium car- 

 bonate (care being taken that the entire residue is acted upon) treated 

 with water and a few drops of alcohol to dissolve the excess of sodium 

 carbonate and sodium sulphate formed, filtered and carefully washed 

 until all traces of sulphates disappear from the wash water. The con- 

 tents of the filter is digested with hot dilute acetic acid to dissolve 

 barium, strontium, magnesium, and calcium carbonates. It sometimes 

 happens that at this point undissolved iron comes through the filter 

 and can not be washed out. In such a case ammonia is added to the 

 filtrate to alkalinity; it is then heated to coagulate the iron, filtered 

 again, and washed. The filtrate is now made very slightly acid with 

 acetic acid and about fifty times the weight of the combined sulphates 

 is added in ammonium sulphate, which ammonium sulphate is dissolved 

 in four times its weight of water. The whole is heated on the steam 

 bath till the sulphates of barium and strontium settle out and is allowed 

 to stand over night. 



The precipitated sulphates are filtered and washed with a concen- 

 trated solution of ammonium sulphate till no more calcium is present 

 in the wash water. The filter is ignited to a white ash, then treated 

 with a few drops of sulphuric acid, ignited again, and weighed. The 

 residue thus obtained consists of barium and strontium sulphates. This 

 residue is then digested for twenty-four hours (with frequent stirring) 

 with ammonium carbonate solution to change the strontium sulphate to 

 strontium carbonate. The residue remaining is transferred to a filter, 

 washed, and the strontium carbonate dissolved out with dilute hydro- 

 chloric acid. The residue is then washed, ignited as before, and finally 

 weighed as barium sulphate. The difference between the last weight 



U. S. Dept. Agr., Bureau of Chemistry, Bui. 46, rev., p. 13. 

 & Gooch and Whitford, U. S. Geological Survey, Bui. 47. 



