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