“…(1 /S'), where = 1,2, or 3, a is the mole fraction of ammonia, and S is the inlet space velocity (2,4,8,9). Recent workers (9) have used n -2, which is identical to Equation 1, and this equation is obtained by both contact-time and flow-balance derivations (7). The three definitions lead to only small numerical differences, as the term (1 + a) usually has a value between 1.00 and 1.10.…”