Thermal Analysis of Magnesite at CO 2 Pressures up to Six Atmospheres

The literature contains contradictory statements that the decomposition of magnesite is and is not affected by the pressure of CO 2 during the decomposition reaction. By means of the new variable‐pressure differential thermal analysis technique, samples of Washington and Nevada magnesites were run at CO 2 pressures over the range 0.001 to 5000 mm. Hg. At 0.001 mm. Hg the endothermic loop starts at approximately 350°C., at 500° C. for 1 atmosphere of CO 2 , and at 612°C. under 5000 mm. Hg pressure of CO 2 . The results permit straightforward analysis of the mechanics of decomposition and comply with the Clausius‐Clapeyron and Van't Hoff equations at CO 2 pressures above 250 mm. Hg.