This test method covers the procedures for determining soluble sulfate ions present in water or a filtrate using a photometer to measure the turbidity of precipitated barium sulfate. This test method also details a method for standardizing the photometer to be used. The soluble sulfate ions may be removed from clays or clay-water slurries by leaching with water during mixing and then filter pressing. An impractical number of washings would be needed to remove all sulfate ions, therefore, this test method should be considered only as a control test and not a quantitative analysis for sulfate ions. Test apparatus include a balance, high speed mixer, filter press, glass beakers, transfer pipets, spectrophotometer, measuring spoon, and other laboratory equipment. All reagents to be used should be of the required purity and concentration.

1.1 This test method covers the determination of soluble sulfate ions present in water or a filtrate by means of a photometer measuring the turbidity of precipitated barium sulfate. A method of standardizing the photometer for this test method is also given.

1.2 Soluble sulfate ions may be removed from clays or clay-water slurries by leaching with water during mixing and subsequent filter pressing. To remove all the sulfate ions would require an impractical number of washings; therefore, this test method should be considered a control test and not a quantitative analysis for SO₄ ions.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.