THE Department of Scientific and Industrial Re search has issued a revised edition of a bulletin published some years ago on “The Properties of Breeze and Clinker Aggregates and Methods of Testing their Soundness” (Building Research Bulletin No. 5. London: H,M. Stationery Office. Qd. net). Since the original publication, investigations carried out at the Building Research Station have established the cause of the occasional failures of these materials and have enabled tests to be devised which are suitable for application under ordinary working conditions.