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