ABSTRACT 



An instrument is described which continuously measures the concentra- 

 tion of dissolved gases in liquids. The operation of the instrument is based on 

 the establishment of equilibrium between the continuously flowing liquid sample 

 and a gas space of constant volume. The equilibrium pressure in the gas space 

 indicates the concentration of dissolved gases. Experimental confirmation of the 

 validity of the method is presented for air dissolved in water. The design of a 

 practical instrument and criteria for its improvemeni, are given. 



INTRODUCTION 



Methods of determining the concentration of dissolved gases in liquids find applica- 

 tions in such fields as medical and biological research, chemical industries, operation of 

 steam turbines, and hydrodynamic research. The necessity for control of the air content in 

 water used in cavitation experiments has long been recognized. Procedures for testing model 

 ship propellers in variable-pressure water tunnels have included the standardization of the 

 air content of the water in the tunnel. ^'-^ Whereas, in general, higher air content appears to 

 make for inception of cavitation at higher local pressures,^ experiments and observations on 

 this and various other effects of dissolved air are neither complete nor in total agreement. 

 Continued interest in the role of air, both dissolved and undissolved, in cavitation phenomena 

 is directed not only toward the standardization of water-tunnel test procedures but also to- 

 ward fundamental studies of inception, growth, and collapse of cavities and of the noise 

 and erosion produced. 



Methods employed at the David Taylor Model Basin for the determination of the air 

 content of water used in cavitation experiments have included the Winkler chemical test for 

 dissolved oxygen,'* the Cambridge Instrument Company's meter which measures the thermal 

 conductivity of the extracted gases, ^ and the method of Van Slyke.^ In this last, the dis- 

 solved gases in a measured sample of the solution are extracted under a Torricellian vacuum 

 and the pressure of the extracted gases is measured upon recompression to a specified volume. 

 The various methods of measurement do not, in general, determine directly the same physical 

 quantity, especially if the solution is of a mixture of gases having different solubilities. 



This report describes a method for obtaining a continuous indication of gas content, 

 discusses some of the principles involved in the design and operation of an instrument employ- 

 ing the method, presents experimental confirmation of its feasibility, and provides design in- 

 formation necessary for construction of a practical instrument 



References are listed on page IS 



