The study was undertaken to identify the basic factors involved in the capsure of SO2 by limestone or dolomite added with the fuel or blown separately into the hot flue gas of central-station boiler furnaces. It has been known for many years that lime and magnesia will react with SO2 to form calcium and magnesium sulfates in boiler furnaces, but the basic limiting conditions under which these reactions can occur have never been adequately defined. It was the objective of this brief study to provide that information. The report is in three parts, following a brief introduction: thermodynamic considerations, kinetics, and recommendations for use in the field. An extensive appendix tabulates the results of the many thermochemical calculations made during this study. (Author)