a cylindrical enclosure 1 having at one end a gas inlet 2 and at the opposite end a gas outlet 3 two electrodes 4 and 5 are disposed one in front of the other inside the enclosure and are connected via heat resistant conductors 6 and 7 made for example of sic to a dc source not shown which is disposed outside the furnace as can be seen in fig2 in more detail the electrodes are shell shaped the concave surfaces facing each other fig1 further shows a sample 8 between the two electrodes this sample being supported by a sample holder 9 made of an electrically insulating ceramic material the dimension of the main surface of the electrodes is selected at least 1 5 times as large as the corresponding dimension of the required partial volume of reduced oxygen partial pressure which is located in the central area between the two electrodes it is assumed that the furnace ensures the required high temperature of above 1000 u00b0 c to the inner volume of the enclosure 1 a sample 8 whose corrosion behaviour is to be studied in the presence of a given gas atmosphere is placed on the sample holder 9 the gas mixture injected through the inlet 2 differs from this defined atmosphere by the fact that its oxygen partial pressure is by orders.