This is important for analysis in the very low ppm range. The crucibles are inserted into the
furnace tube and they remain preheated in the tube until needed. Each time a crucible is
needed, a new one is inserted into the tube, and a preheated crucible falls out the other end of
the furnace tube. The recommended pre-heating temperature is between 1250°C and 1350°C.
For preheating crucibles the boat stop is removed.