Cover for sealing open mouth of a container

A cover for sealing an open mouth of a container, which comprises a top member and a cylindrical skirt depending from said top member;

• said top member having means for retaining substances on an interior surface of said top member for treating contents of the container;
• said top member comprising a peripheral section adjacent said skirt, a concave section in the center thereof, a convex section between said peripheral and concave sections, and a raised portion constituting a continuation of said convex section, extending diametrically across said concave section and connected to said concave section by generally parallel vertical walls;
• said raised portion and said walls defining said means;
• said walls being coupled by a pair of generally parallel, vertical reinforcing members;
• said peripheral section comprising a cylindrical protrusion coaxial with said skirt, extending in a direction opposite to that of said skirt, having lateral dimensions less than those of said skirt and coupled to said protrusion by a ledge member extending perpendicular to said skirt and protrusion to form a stepped outer profile on the cover;
• said convex section of said top member being coupled to said protrusion by a horizontal member oriented perpendicular to said protrusion and extending inwardly from a lateral surface of said protrusion at a location spaced from a top edge of said protrusion;
• said concave and convex sections being located entirely below said top edge of said protrusion and not above said horizontal member.