{HEAD ~ Phosphoric acid} with {TAIL ~ 5 to 20% concentration} is added drop by drop to the solution while stirring 
{ HEAD ~ Phosphoric acid } with { TAIL ~ 5 to 20 % concentration } is added drop by drop to the solution while stirring
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH