This is a report issued in 1974 by the American Society of Testing and Materials. This method, which is applicable only to portland cements, covers the determination of the expansion of mortar bars made from a mixture of portland cement and gypsum in such proportions that the mixture has an SO3 content of 7.0 weight percent. This method is intended primarily for use by those interested in research on methods for determining the potential sulfate resistance of portland cement.