Immersion time/5 to 10 sec. If you want a scratch-brushed finish, immerse the part in the arsenic trioxide solution, rinse, brush wet, and re-immerse for recoloring. The coating is a displacement film of arsenic which has relatively little resistance to abrasion. Formula No. Ferric chloride (6H4O) or ferric sulfate (9H2O)/15 oz/gal Immersion time/10 sec. Hydrochloric acid (35%)/1 gal Arsenic trioxide/13 to 14 oz/gal Arsenic trioxide/4 oz/gal Hydrochloric acid (1.20 sp gr)/8.5 fl oz/gal Sulfuric acid (1.84 sp gr)/2 fl oz/gal Temperature/70 to 80'F Temperature/70 to 80'F