A generally applicable test using dolomite to detect effects of atmosphere self-generation and to determine atmosphere control in thermal analysis is demonstrated. Either differential thermal analysis (DTA) or thermogravimetry (TG) can be used. In a CO2 atmosphere dolomite produces two separate thermal decompositions, but in a CO2-free atmosphere dolomite decomposes in a single reaction. If two peaks or a shoulder appear on the decomposition response in air, effects of self-generated CO2 are proven. If the reaction in air is not complete by 800 degrees C, self-generated CO2 around the sample is strongly indicated. The dolomite decomposition at lower temperature in CO2 essentially independent of CO2 pressure, can be used to establish a temperature reference point for this atmosphere testing. Thin layers of sample and a gas stream flowing over the sample are shown to be necessary for atmosphere control in thermal analysis.