57 of chamber 50 of the preferred embodiment are positioned such that first outlet 55 is positioned in the top portion 53 of chamber 50 at temperature t 4 the second outlet 56 is positioned below first outlet 55 at a temperature t 5 and third outlet 57 is positioned below second outlet 56 but above the bottom portion 51 of chamber 50 and is at temperature t 6 upon the application of heat by heater 54 to the bottom portion 51 of chamber 50 the silicon tetraiodide and the other impurity iodides are vaporized and driven upwardly through the chamber 50 at the first outlet 55 temperature t 4 is about 120 u00b0 c and the vaporized impurity iodides that have lower boiling points than silicon tetraiodide vapor i e bi 3 and pi 3 condense as is indicated by droplets 17 and are collected by annular catch ring 43 and removed from chamber 50 at a cold trap similar to the way that the impurity iodides are trapped in and removed from the cold wall reaction chamber 20 as disclosed above similarly at the second outlet 56 temperature t 5 is about 180 u00b0 c the temperature at which silicon tetraiodide condenses as shown by.