A Safe Vacuum Manometer Standard vacuum manometers for water pumps or for measuring low vacuums are usually made of 760-mm-long glass tubes, but they are mostly used to read pressure in alimited region of the scale. Furthermore, these manometers necessitate large quantities of mercury, and, hence, they are a constant hazard because of mercury spills and water contamination. We found it convenient to replace the old manometers in our laboratories with the home-built apparatuses illustrated in detail in the figure. Working conditions are obtained by introducing the required quantity of mercury into the U-tube and applying high vacuum while keeping it in the horizontal position. When a good vacuum is reached (-0.01 mm) the U-tube is turned upright and air is allowed to enter slowly. The mercury will occupy the tube as shown in the figure and the device is ready. The pressure will then be read, as in any other differential manometer, as the difference between the two levels of mercury. Our proposed manometer is a modification of the usual differential manometers and is suoerior in sim~licitv . . of construction and use, dimensions, and, above all, safety against mercury spills.
Gian Franco Miozzo Dipartimento di Chimica Olganica Via Manolo, 1 35131 Padova, Italy
826
Journal of Chemical Education
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