passing said reactants at a known preselected concentration through {HEAD ~ said bundle} of parallel tubes wherein the inlet temperature is high enough to initiate said {TAIL ~ catalytic conversion} throughout said volume of catalyst 
passing said reactants at a known preselected concentration through { HEAD ~ said bundle } of parallel tubes wherein the inlet temperature is high enough to initiate said { TAIL ~ catalytic conversion } throughout said volume of catalyst
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH