The rate of hardening, or polymerization, of adhesive can be controlled by varying {TAIL ~ the concentration} of catalyst in {HEAD ~ the catalyst solution} 
The rate of hardening , or polymerization , of adhesive can be controlled by varying { TAIL ~ the concentration } of catalyst in { HEAD ~ the catalyst solution }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD