The anode holder shown in figure 2 was designed with two goals in mind. The heat losses of the holder were to be reduced as far as possible and they should be such that an accurate heat balance can be made. In order to reduce the number of variable parameters, all experiments were made with a constant arc length of 0.5'' and a current of 100 Amp. The argon flow through the porous anode was varied systematically between **f. and **f. The lower limit was determined by the fact that for smaller flow rates the arc started to strike to the anode holder instead of to the porous graphite plug and that it became highly unstable. The upper limit was determined by the difficulty of measuring the characteristic anode surface temperature (see below) since only a small region of the anode was struck by the arc. This region which had a higher temperature than the rest of the anode surface changed size and location continuously.

For each mass flow rate the arc voltage was measured. To measure the surface temperature of the anode plug, the surface was scanned with a pyrometer. As it turned out, a very hot region occurred on the plug. Its temperature was denoted by **f. The size of this hot region was estimated by eye. The rest of the surface had a temperature which decreased towards the outer diameter of the plug. The mean temperature of this region was approximated by the temperature measured halfways between the edge of the hot spot and the rim of the plug. It was denoted by **f. The mean temperature of the surface was then computed according to the following relation: **f where x is the fraction of the plug area covered by the hot spot. Assuming thermal equilibrium between the anode surface and the transpiring argon, the gas enthalpy rise through the anode was calculated according to the relation **f whereby the specific heat of argon was taken as **f. This calculation results in an enthalpy rise which is somewhat high because it assumes a mass flow equally distributed over the plug cross section whereas in reality the mass velocity is expected to be smaller in the regions of higher temperatures.