When arcing powder samples in graphite cupped electrodes using the dc arc the charge is sometimes ejected from the cup due to the sudden evolution of vapor produced by the rapid heating. The practice of venting the packed electrode by pricking into the charge with a pin is not particularly effective in preventing ejection. A more effective method which overcomes the difficulty is to vent the cup at the bottom before filling. This is carried out by drilling two small holes through the cup wall, the holes being diametrically opposed and just above the floor of the cup.
L. Toft and G. A. Roworth, "Vented Cupped Electrodes," Appl. Spectrosc. 24, 132-132 (1970)