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