The following limit tests are provided as general procedures for use where limits for chloride and sulfate are specified in the individual monographs.

Perform the tests and the controls in glass cylinders of the same diameter and matched as closely as practicable in other respects (see Visual Comparisonunder Spectrophotometry and Light-Scattering á851ñ).Use the same quantities of the same reagents for both the solution under test and the control solution containing the specified volume of chloride or sulfate.If,after acidification,the solution is not perfectly clear,pass it through a filter paper that gives negative tests for chloride and sulfate.Add the precipitant,silver nitrate TSor barium chloride TSas required,to both the test solution and the control solution in immediate sequence.

Where the individual monograph calls for applying the test to a specific volume of a solution of the substance,and the limit for chloride or sulfate corresponds to 0.20mLor less of 0.020Nhydrochloric acid or sulfuric acid,respectively,apply the test to the solution without further dilution.In such cases maintain the same volume relationships for the control solution as specified for the solution under test.In applying the test to the salts of heavy metals,which normally show an acid reaction,omit the acidification and do not neutralize the solution.Dissolve bismuth salts in a few mLof water and 2mLof nitric acid before treating with the precipitant.