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