A General Electric analytical mass spectrometer, which was originally designed only for gaseous samples, has been modified so that the sample system can be converted for application to solid samples at elevated temperatures up to 1000°C. Conversion is accomplished by the complete replacement of the sample system by a magnetically operated device and a cavity furnace, the heater of which is thermally attached to the furnace body and servo‐controlled to keep to the predetermined temperature within a fraction of a degree. The furnace body is a silica tube, 5 mm i.d. Replacement of the sample can be done within 10 min without breaking the major vacuum. Advantages and disadvantages compared to the Knudsen cell are also discussed.