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) OURNAL OF CHEMICAL EDUCATION
SOME USES FOR MODELING CLAY IN THE CHEMICAL LABORATORY W. F. BRUCE Cornell University, Ithaca, New York
WHILE modeling clay finds frequent use in a biologicallaboratory for sealing anaerobic jars and Petrie plates or for holdmg tubes, it is seldom encountered in a chemical laboratory. An account of some of the uses which chemists may make of the rather unique properties of this material therefore appears worth while. The most obvious use of modeling clay is in the making of models. From a number of balls of modeling clay and some matches simple atomic or molecular models can easily be constructed. Models of the energy levels of reactions for use in the study of quantum mechanics can conveniently be fashioned from this material. Models of the various crystal forms may be made, a process which may be useful in instruction. A use taken from the experience of the biological laboratory is the sealing of flasks and vials with modeting clay. Although the clay is relatively impervious to water, it is partially dissolved by many of the common organic solvents, with the result that it cannot long be used to coufme organic vapors. I t can nevertheless be nsed successfully in forming a temporary seal. This is particularly satisfactory in closing ampoules to which the section cut from the stem can be fitted tightly and held in place by modeling clay. Since the clay is fairly heavy (d. 1.6), it can be used in the form of rings to bold small vessels upright in water or ice baths. Because the material rapidly loses its coherence a t higher temperatures most of its uses are limited to temperatures below 50°C. Uses of modeling clay which depend on the ability of the material to adhere to dry glass are of special interest to the chemist. A small pan of clay will hold upright the small filtering flasks which without support frequently tend to overturn in the midst of a filtration. As the accompanying photograph shows, this arrangement is remarkable for its simplicity and convenience. By giving the flask a quick pressure toward one side the vessel can readily be removed, emptied, and set up again by pressing it against the plate with a twisting motion, all in a fraction of the time required to operate a clamp. By occasionally exposing fresh surfaces of
clay and by keeping the material and the exterior of the flasks free from solvents and moisture, the support furnished by this device is practically as reliable as that provided by a stand and clamp. If by accident either the clay or the exterior of the vessel is wet by water or solvents, the surfaces of both should be carefully dried before the plate is nsed again. The clay gradually hardens, and after about a year of use should be replaced. The clay-containing plate can also be used for holding round-bottomed vessels over a wide range of shapes and sizes. Care should be taken, however, that the downward projection of the center of gravity of the vessel falls within or near the area in contact with the clay, for if this condition is not fulfilled a heavy vessel may gradually pull loose from the plate. When modeling clay is once introduced into the laboratory, a multitude of new uses will undoubtedly be discovered.
