The strength of {TAIL ~ the bond} can be varied by varying {HEAD ~ the amount} of the impregnant 
The strength of { TAIL ~ the bond } can be varied by varying { HEAD ~ the amount } of the impregnant
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH