Abstract: A cover for a laboratory beaker is formed from a top structure having a depending, annular skirt that forms, with the frustoconically shaped top structure, a peripheral shoulder. The skirt is dimensioned to be received by the opening of beaker to hold the cover in place, and to close any poring spout that may be formed in the periphery of the beaker. The shoulder is dimensioned to rest on the periphery of the beaker. Formed in top structure is an aperture that allows ingress to the beaker when the cover is in place. A stopper is provided to be removably received by the aperture to close the interior of the beaker. The a bottom portion of the stopper is structured to depend from the top structure, toward the volume of the beaker covered by the cover to provide a formation for reflux activity.