second mounting means disposed on said trap for alternately mounting said trap on {HEAD ~ a horizontal wall} of {TAIL ~ said furnace} 
second mounting means disposed on said trap for alternately mounting said trap on { HEAD ~ a horizontal wall } of { TAIL ~ said furnace }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL