IntroductionSeveral methods are employed in elementary qualitative analysis for the separation of strontium from calcium and the subsequent detection of the latter. The one which appears to be in most general use is that involving the precipitation of strontium as sulfate and its removal by filtration, followed by the detection of calcium as calcium oxalate by adding ammonium oxalate to the filtrate. While using this method in elementary classes the attention of the writers was called to the fact that if strontium is present considerable uncertainty is introduced into the calcium test, in as much as an appreciable precipitate of strontium oxalate is almost always obtained. Calcium is, therefore, often reported when absent since the white strontium oxalate is indistinguishable in appearance from the corresponding calcium salt. Such confusion may be obviated to some extent through confirmation by means of a flame test. Nevertheless, it would appear to be much more satisfactory, especially from a pedagogic standpoint, if conditions could be so adjusted that the strontium oxalate precipitate would not form a t all, and at the same time the sensitivity of the calcium test be not appreciably affected. The great diierence in the solubilities of the oxalates of the two metals suggests that such an adjustment might not be impossible.As early as 1886 Bloxaml pointed out that after strontium has supposedly been removed with sulfuric acid, the solution will still give a precipitate on the addition of an oxalate. Arzruni2 remarked that the filtrate from the precipitation of strontium by a soluble sulfate will yield a precipitate of strontium oxalate. Ebler3 noticed that in the separation of the alkaline earth metals strontium oxalate may come down with calcium oxalate when the filtrate from the sulfate precipitate is tested for calcium. He recommended diluting the filtrate with an equal volume of water before adding ammonium oxalate.
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