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