Attempts have been made to study the homogeneous dissociation kinetics of N2F4and OF2by means of an adiabatic compression apparatus attached to the fast reaction cell of a Bendix time‐of‐flight mass spectrometer. It was found that, if helium is used for the reaction medium, temperatures sufficiently high for reaction to occur are not obtained, nor is the maximum temperature obtained constant for a significant period of time; i.e., the high thermal conductivity of helium does not permit an approach to adiabatic operation. A further bar to successful experimentation (assuming that the nonadiabaticity could have been overcome by using an inert medium of lower thermal conductivity) was the self‐destructiveness of the light weight apparatus and the damage to the ion source of the mass spectrometer, brought about by the impact of the piston at the end of the compression stroke. The experimental data obtained in this system with helium, argon, and nitrogen are critically examined and possible theoretical limits of mechanical adiabatic compression, proposed by Vernotte, are discussed.