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