Zinc oxnO), not less than 99 percent. Loss on ignition at 800 C, not more than 1 percent. Cadmium (as Cd), not more than 15 parts per million. Mercury (as Hg), not more than 1 part per million. Arsenic (as As), not more than 3 parts per million. Lead (as Pb), not more than 20 parts per million.