No.1 a. clean the surface in perchloroethylene or trichloroethylene solvent. (Vapor-degreasing practices are also widely used, and would be preferable for high-speed commercial production.) b. Air-dry the surface (the higher metal temperature in a vapordegreasing operation would cause more rapid drying). c. Submerge the cleaned aluminum surface for 10 min in a 150'-155'F solution of 10 parts by weight of concentrated sulfuric acid to 1 part of sodium dichromate to 30 parts of distilled water. d. flush the treated surface with fresh water, submerge the part, remove and air-dry at room temperature or, preferably, at temperatures to 150'F. e. Solution requires lead-lined tank and adequate exhaust system. No.2 a. Clean the surface in perchloroethylene or trichloroethylene. (Vapor-degreasing practices are also widely used, and would be preferable for highspeed commercial production.) b. Air-dry the surface (the higher metal temperature in a vapordegreasing operation permits more rapid dryi
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