This Part of BS 812 describes the method for determining the soundness of aggregates by subjecting the aggregate to cycles of immersion in a saturated solution of magnesium sulphate followed by oven-drying. The method is applicable to aggregate passing a 14.0 mm test sieve but is retained on a 10.0 mm test sieve. NOTE 1 The majority of aggregates can be tested for soundness using this method. Precision has been established for the rock types listed in Table 1. The test may not be suitable for all rock types and reservations have been expressed elsewhere in respect of some carbonate aggregates and some aggregates having a high proportion of magnesium bearing minerals or of cryptocrystalline quartz. For other size fractions, a recommended method is described in appendix A. NOTE 2 The titles of the publications referred to in this standard are listed on the inside back cover.