CHICAGO (AP) _ Grain futures were mixed Tuesday on the Chicago Board of Trade. Sept. corn gained 7.5 cents at $5.22 a bushel. Sept. wheat was down 6.25 cents at $7.66 a bushel. Sept. oats was unchanged at $3.56 a bushel. Sept. soybeans was unchanged at $13.04 a bushel. Beef was lower and pork was...