. . . . "The coatings insoluble in an acidic medium may be formed from polymers such as cellulose acetate phthalate, cellulose acetate mellitate, cellulose acetate succinate, hydroxypropylmethylcellulose phthalate, hydroxypropylmethylcellulose acetate succinate, carboxymethylcellulose ether, polyvinylacetate phthalate, polyester of styrene and maleic acid copolymer, polyester of vinylether and maleic acid" .