“…Determination of zirconium and hafnium, alone or together has largely been done gravimetricallv-e.g., precipitation by cupferron (21,22,33), mandelic acid and its derivatives (7,12,16,23,26,27), phosphates (20,37), selenous acid (32,34), substituted arsonic acids (29), or hydrolysis (36), followed by ignition to the oxide. Proposed titrimetric methods include an amperometric one using p-nitrophenylarsonic acid (13)•, the exacting conditions necessary to obtain even fair results on pure zirconium solutions and the apparent large solubility of the precipitate cited by the authors (who did not investigate interferences) appear to make the method of limited value.…”