An Inexpensive Water Leveling Device for Gas Law Experiments John H. Bedenbaugh and Angela 0. Bedenbaugh University of Southern Mississippi, Hattiesburg, MS 39406
In many of the gas law experiments found in general chemistry and high school chemistry laboratory texts, a graduated cylinder is used to measure the volume of water displaced by the gas. The procedure is cumbersome and inaccurate. We have recently developed for the general chemistry course several gas law experiments utilizing a closed system in which the volume of displaced water is measured in a buret. Thus the evolution of an insoluble gas displaces a measured volume of water from the buret into a leveling bulb that is raised and lowered as required to equalize pressures within and without the system. It has been brought to our attention that virtually no high school chemistry stockroom and few college-level general chemistry storerooms maintain a supply of leveling bulbs. This is not surprising since these bulbs currently are priced at about $20 each. Funnels or thistle tubes are sometimes used instead of leveling bulbs, hut both of these substitutes have disadvantages. We have developed an inexpensive substitute for the traditional glass leveling bulb that also eliminates the need for an iron support ring required to hold the bulb. (These rings cnst about $5.) Our amaratus can be constructed in amatter .. of minutes from readily available materials. The"homemade" leveline bulh and clamr, (see tieure) has worked successfully in the Lands of numerck studintsover a three-vear - oeriod. The water container is an inverted 16-02 clear plastic soft drink bottle with a hole in its bottom and its top fitted with a one-hole rubber stopper equipped with a glass tube. Two stout rubher bands 6-12 mm in width are used to strap the bottle securely to one of the two gripping surfaces of a snack bag clamp. The finger holds of the clamp are compressed to spread apart the gripping surfaces and place them around the upright rod of a ring stand. When the finger holds are released, the gripping surfaces hold the bottle securely in place even when it is filled with water. The clamp permits the bottle to be quickly and accurately placed at anv noint on the rod reauired to eoualize the water Dressure h i h e buret. The necessarv hole in the bottom of the olastic bottle could conceivabiy he made using a power drilion a securely fastened bottle. We prefer the use of heat to form the hole. Our procedure requires two Meker burners. One burner, stripped of hose and flame spreader tip, is our tool. The opening of this burner is heated to a high temperature in the flame from the other burner. Then the heated burner tip is pressed against the bottom of a plastic bottle. The plastic melts, forming the required hole and a plastic disk, which is
discarded. Obviously this procedure must be done with great care and proper protection to prevent burns. It should be done only in a hood so that the fumes produced are not inhaled. This inexpensive leveling device for equalization of pressures has application in any experiment in which a traditional leveling bulh is used to equalize water levels. It should not, however, be used with acids, bases, or organic liquids, which might degrade or dissolve the plastic bottle. Neither should the apparatus be used with mercury; the great mass involved could conceivably overload the system causing it to collapse and spill the mercury.
Volume 68 Number 8 August 1991
673
