Improvement in a Charles' Law Capillary Tube Experiment for lntroducfory Chemistry Laboratory Capillary tube experiments require a minimum of equipment, incur a minimum of breakage, and are well suited for use with large classes. In such an experiment designed to illustrate Charles' Law, the temperature is usually varied from room temperature to about 100°C. With this small temperature range, which is rather far removed from absolute zero, we have found it difficult t o determine the slope sceurately enough to get good class results for the value of absolute zero. We have improved the socuracy of the experiment greatly by introducing s. volume-temperature measurement at about -80°C using a. Dry Ice-acetone cooling mixture in addition to the three other measurements. These other measurements are taken at oil bath temperatures, room temperature, and ice bath temperature. This single additional point on the graph, Located much closer to absolute zero than the others, results in a more accurste slope and much less "scattering" of students results. In our experiments we use an oil plug which is drawn into the tube as the tube, originally filled with gas in the oil bath at about 10O0C, is withdrawn and allowed to cool to room temperature. This oil plug serves as a marker 60 indicate the volume of enclosed gas at constant pressure in the subsequent measurements. The fact that the oil plug congeals when it is finally dipped into the Dry-Ice acetone mixture is very convenient making it possible to remove the tube from the bath and to have a minute or so to measure the volume before the oil plug melts and its position changes. We have found that one such bath, as well as one of each of the other baths, can easily take care of the needs of a class of about 24 students. ALBERTK. SAWYER UNIVERSITY O F NEWHAMPSHIRE DURHAM, NEWHAMPSAIRE 03824
Volume 47, Number 8, August 1970
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