OCTOBER, 1951
A LABORATORY PRESSURE REGULATOR GEORGE G. LOWRY Stanford University, Stanford. California
WHEN performing low-pressure distillations in the laboratory, one of the major problems is that of keeping the pressure constant. A number of devices have been described for this purpose. A controllable constant-leak device can be made in a few minutes from materials available in every laboratory. This consists of a piece of small-diameter gum rubber tubing, B, attached to a glass T-joint, A, with a fairly tight roll of tissue paper, C, forced into the tubing. In operation, the T-joint with tubing attached is installed in the vacuum system, and the amount of leak is controlled by means of a small screw compressor, D. As long as the source of vacuum remains fairly steady, the pressure in the system remains constant within surprisingly small limits. A unit of this type used in conjunction with a Nelson mechanical pump and a one-liter surge chamber was found to be capable of controlling the pressure within less than 1 mm. a t pressures as low as 5 mm. With a static system (closed, no distillation) this apparatus held a pressure of 12.0 mm. so steadily for one and one- apparatus was found to hold the pressure constant half hours that no fluctuation could he observed with throughout the operation. This device worked with a an ordinary U-tube manometer. During several dis- water aspirator also, but large fluctuations in water tillations a t pressures ranging from 10 to 50 mm. the pressure had a marked effect on the system.
