semiconductor devices such as integrated circuits and discrete transistors are mounted on cards and the cards are installed on raised racks extending up from the bottom of a tank forming a burn - in chamber . the racks are individually lowered to immerse the cards and operating devices in a bath of liquid heat exchange medium at an elevated temperature . the racks are individually accessible through aligned segments of a segmented cover to reduce the intrusion of room water vapor into the burn - in chamber . the elevated temperature of the medium is maintained during the procedure by pumping the medium over mechanical cooling coils to remove excess heat produced by the operating devices . a lead screw and lever mechanical combination provide variable speed pumping , to accommodate changes in medium viscosity , from a fixed speed motor . the pumping also mixes the medium around the cards and devices to produce uniformity in the medium temperature . medium and water vapors in the chamber are blown across acid absorbing material to hydrofluouric acid vapors and then across condensor coils to change them to liquids for conserving the expensive medium . the liquid water is separated from the intermixed liquids from the condensor in a separator that has deep wells and an electrode and bridge circuit to indicate the presence of a certain quantity of liquid water . the liquid water is discarded and the liquid medium is returned to the burn - in chamber . a filter removes particulate and chemical contaminates from the liquid medium , and a weir assembly channels contaminates that float on top of the medium to an agitation box and therefrom to the filter .