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