THEORY 



PRINCIPLE OF OPERATION 



The basic components illustrating the principle of operation are sketched in Figure 1. 

 A continuously flowing sample of the liquid is sprayed into the upper part of a closed cham- 

 ber and subsequently falls to the bottom or runs down the inside walls of the chamber. Liquid 

 is continuously withdrawn from the bottom of the chamber; the inflow and outflow rates are 

 controlled so that the volume of the gas space in the upper portion of the chamber remains 

 constant. The outflowing sample liquid, once having passed through the meter chamber is 

 either returned to the reservoir from which it was taken or disposed of in whatever manner is 

 convenient. Thus, the sample liquid being exposed to the gas space within the chamber is 

 renewed continually. If, with respect to its dissolved gas content, the incoming liquid is in 

 equilibrium with the partial pressure of each gas trapped in the gas space in the upper portion 

 of the chamber, no net exchange of gas will take place between the flowing liquid and the gas 

 space. If, however, the partial pressure of any gas in the gas space is different from the 

 pressure corresponding to equilibrium with the concentration of that gas in solution in the in- 

 coming liquid, an exchange will take place and gas will be evolved or absorbed by the liquid 

 until the quantity of that gas in the gas space is just sufficient to exert the pressure corres- 

 ponding to equilibrium with the concentration of that gas in the incoming liquid. The result 

 is that the pressure in the chamber approaches an equilibrium value indicative of the concen- 

 tration of dissolved gas in the sample liquid. The pressure is 

 measured by any ordinary means connected to the chamber. 

 Proper account must be taken of the pressure due to the vapor 

 of the solvent. 



It is manifest that an instrument operating on the princi- 

 ple just described will give the correct indication if the flow 

 of liquid through the chamber is slow enough so that actual 

 equilibrium is maintained between the outgoing liquid and the 

 gas trapped in the gas space. This is true since, in the limit 

 of extremely slow flow and long exposure, the pressure of each 

 gas in the gas space will, in fact, reach equilibrium with the 

 concentration of dissolved gas in the liquid. It is necessary 

 to determine by experiment, however, whether the instrument 

 can be made to operate under practical requirements, such as 

 workable physical size and flow rate, sufficiently rapid ap- 

 proach to equilibrium, and freedom from perturbation of the 

 equilibrium pressure caused by the methods employed to pro- 

 duce the required amount of mixing and exposure of the liquid. 

 These requirements are closely interdependent. An under- 

 standing of the relations involved will be facilitated by a 



Figure 1 - Basic Form of 

 Meter Chamber 



