Apparatus for Imposing and Measuring Rapid Pressure Changes in Gases

A simple apparatus is described in which rapid volume changes can be imposed on a small reaction vessel by means of a bellows and cam arrangement. Thus pressure increments of the order of 10 mm Hg can be induced in about 2 milliseconds. The pressure changes during the expansion or compression, and the subsequent adjustment to equilibrium in case the vessel is filled with a dissociating gas is followed by a Massa Sound pick-up (piezoelectric unit). The sensitivity of the apparatus is such that a Δp=6.7 mm gives an inch deflection on the oscilloscope. Limitations of the present design, and possible improvements for increased stability and sensitivity are discussed.