Elmer R. Trumbull
Colgote University Hamilton, New York
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A Simale Closed End Manometer
There are frequent uses in the laboratory for simple manometers to measure pressures in the range of 1-100 mm of mercury. The i~lstrument described here has been used by our students in introductory organic chemistry and has demonstrated certain advantages over previous designs. Probably the most significant is the fact that the glass tuhing by which the manometer is attached to the evacuated system is not rigidly connected to the manometer tube proper aud breakage in assembling and taking down the systems is greatly reduced. I n use the instrument can be held in standard clamps and a number of manometers can he stored in a small space in a box with suitable compartments to hold the tubes in a vertical position. The design minimizes spillage of mercury. I n so far as possible the manometer is constructed from standard glassware. The outer tube is a 38 X 200 mm test tube fitted with a no. 8 two-holed stopper. To connect the manometer to the evacuated system a length of 8 mm tuhing or a T-tube may be used, although for permanent installations there are advantages to the use of a stopcock. The manometer tube proper is constructed from a 12in. length of 7 mm tubing, a short piece of rod of the same diameter, and a test tube 16-18 mrn in diameter. The bend a t the bottom of the tube can be made smoothly in the flame of a Meeker burner when 7 mm borosilicate glass is used. The only point to note is the location of the hole in the side of the large tubing. This should he placed so that all the mercury needed for the column can be contained in the reservoir when the manometer is inverted and can be run in and out of
350
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Journal o f Chemical Education
the tube without losf. A strip of graph paper graduated in millimeters attached to the tube provides an inexpensive scale. To fill the manometer, a suitable amount of mercury is placed in the reservoir. About 1 ml is needed for every 2 in. of column if 7 mm tubing is used. The mercury is conveniently measured and inserted using a 5 ml hypodermic syringe. The outer tube is put in place and the whole system evacuated with a mechanical pump and heated with an infrared lamp if desired. While evacuated, the manometer is righted, taking care that mercury is not lost throueh the hole above the reservoir. Air is-now admitted to the svstern and the manometer is ready for use. When several manometers are to be filled,it is convenient to have a threeway stopcock between the pump and the manometer so that one can be released and another put on the line without disturbing the pump. If the manometer becomes contaminated with volatile materials in use, the mercury can be d r a m back into the reservoir and heated in vacuo until the contaminants are removed. This desien is an amaleamation of types observed by the author in the laboratories of Brown University and at the Nat,ional Research Council of Canada. ~
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