also preferred that the kiln 10 be a vacuum type kiln 10 and thus the interior of the kiln 10 is connected as indicated by the line 42 to a vacuum pump or the like 44 that produces negative pressure i e pressure below atmospheric within the interior of the kiln 10 at the appropriate time and when the kiln is sealed by known means the signals governing the operation of the system are delivered between the various operating elements and control computer or the like 50 via control lines as indicated as dot dash lines 51 in fig1 and 3 a first embodiment of the electrode connector 15 is shown if fig1 with a single electrically conductive sliding joint 18 joining solid electrically conductive sections or elements 15a and 15b preferably constructed of aluminum which form the connector 15 in this embodiment one of the elements 15a is connected to the electrode 12 while the element 15b is connected to the power source 40 the two discrete elements are electrically interconnect by the sliding connection 18 formed by the element 15a passing through an passage formed at the free end of the element 15b the interaction in the joint or sliding connection 18 maintains the electrical connection between the elements 15a and 15b while permitting relative movement therebetween so that the electrical connection from the source to the electrode is maintained when the electrode is in a lowered or extended.