The installation of the meter is shown schematically in Figure 2. The reservoir for 

 the test water is the 5000-gallon head tank of the Flow Facility. The head tank can be pres- 

 surized or evacuated. The water can be circulated through spray nozzles mounted inside the 

 tank, and thus any desired air content can be obtained. Once established, a given air con- 

 tent can be maintained for hours or even days because of the large volume of water and the 

 low diffusivity of dissolved gases. The pressure in the meter chamber was measured by 

 means of a telemetering pressure recorder (Automatic Temperature Control Co.). The pumps 

 are constant displacement gear pumps (Eastern Industries model GW-1) driven at reduced 

 speed by d-c shunt motors (gearmotors). 



In order to determine more definitely the feasibility of the method and the validity of 

 the analysis presented above, some experimental tests of the meter were conducted. These 

 tests consisted of runs in which an initial displacement of the pressure in the gas-space 

 was effected and the reapproach to equilibrium was monitored and recorded. Before a test 

 run, the meter was allowed to operate until the pressure in the gas space appeared to have 

 reached an equilibrium value. The inflow and outflow rates were carefully regulated manually 

 so that the water level in the sight tube (and hence the volume of the gas space) remained con- 

 stant. After equilibrium had been thus established, the volume of the gas space was allowed 

 to change quickly to a new value either larger or smaller than that which had previously been 

 maintained. The effect of this last action is to simulate a "step" change in the concentra- 

 tion of dissolved gas in the incoming sample since, as a result of the change in volume, the 

 new value of the pressure in the gas space is lower or higher than the equilibrium pressure. 

 The operation of the meter was then continued with the volume of the gas space carefully 

 maintained at the new value and readings were taken at intervals in order to determine the 

 manner in which the pressure returned to the equilibrium values. The flow rate was maintained 

 as nearly constant as possible and its exact value noted and recorded with each pressure 

 reading taken. A thermometer suspended inside the meter chamber indicated the temperature. 



As testing of the meter proceeded, successive modifications were made to improve its 

 performance. Figure i shows details of the arrangement of the nozzles and other components 

 in the upper part of the chamber. For the first two runs, the gas space was unnecessarily 

 large (Figure 4a) and the response time was excessive. A revised version is shown in the 

 sketch of Figure 4b. A micarta core whose volume occupies the greater portion of the glass 

 tube reduces the gas-space volume but not the surface available for exposure of the liquid. 

 The single nozzle was replaced by a triad of nozzles to allow a higher flow rate and thus 

 further decrease the response time. A ramp consisting of flexible plastic tubing wound in a 

 helix about the central core was added to minimize the formation of bubbles. A later addition 

 was the spray baffle. Its purpose was to prevent the spray from clogging the opening of the 

 sight tube. In some of the test runs made before the installation of the baffle, erratic results 

 were obtained because a small slug of water occupied a portion of the vertical section of the 

 sight tube just above the dome, thus introducing errors in the adjustment of the volume of the 

 gas space. 



