An Effective Technique for Cleaning Glassware The removal from glassware of intractable residues, which are not readily dissolved by water or common organic solvents, poses a problem frequently encountered by chemists and students of chemistry. Such residues, for example that are Left in a flask by partially dissolved silicone grease, will yield only to scrubbing or to powerful cleaning solutions. The latter are inconvenient in that prolonged treatment is often required; furthermore, tbeir presence in the laboratory and tbeir use, especially by students, are somewhat hazardous. The application of elbow grease to a soapy testtuhe brush seems a more satisfactory method when feasible, but in many cases the shape of the apparatus being cleaned is such that portiansof its interior are not accessible to a brush. An old trick to solve the problem is to pour a small quantity of sand into the piece of glassware, along with some soap and water or an organic solvent; all openings are then stoppered, and the apparatus is given a few vigomus shakes. The sand of course acts as an abrasive, and usually daes an efficient job of removing all residues from the interior surfaces of the vessel. Unfortunately, one is then confronted with the problems of getting the sand out of the apparatus and properly disposingof it, and the glassware issometimes left with fine scratches in its surface. A slight modification of this method, however, completely eliminates its drawbacks without diminishing its efficiency. The modification is simply the replacement of sand with table salt. While water is of course not suitable as a solvent in this case, a mixture of an organic solvent such as petroleum ether, methylene chloride or acetone and a few grams of salt will, when shaken briefly in a closed piece of glassware, almost invariably remove all residues. The salt is then easily removed and disposed of by rinsing with water. Apparently the edges and corners of the cubic salt crystals are sufficiently sharp and hard to give g o d abrasion, yet cannot scratch a glass surface. The method is applicable to virtually any kind of glassware which can he stoppered up, including nmr sample tubes, pipets, and complex distillation equipment. In cleaning round-bottomed flasks I find it much more convenient than scrubbing with an assortment of curved brushes, none of which ever seems to make contact with the entire inner surface of the vessel.
David P. Higley
University of Missouri-St. Louis St. Louis. 63121
