Abstract: A calorimetric measuring apparatus is provided with a decomposition vessel whose interior is configured as a reaction chamber and which can be tightly sealed, the decomposition vessel being removably arranged inside a jacket, and having at least one temperature sensor for measuring the temperature reached inside the decomposition vessel. Characteristic of the measuring apparatus is that the jacket has a measuring vessel which accommodates the decomposition vessel; at least some areas of the wall zone of this measuring vessel comprise a heat-conductive material; the inner walls of this measuring vessel are spaced from the outer walls of the decomposition vessel, thereby forming an interspace in which a gaseous intermediate medium is provided; and the measuring apparatus has at least a second temperature sensor for measuring the temperature change establishing itself in the heat-conductive wall zone of the measuring vessel.