Using the 100% relative-humidity technique for controlling the mole fraction of water vapor, the Napier (relaxation) frequency of oxygen has been measured as a function of the mole fraction of various water vapors, consisting of pure H20, pure D20, and three mixtures thereof. Pure H20 gives, as is well known, a quadratic in H, the mole fraction; pure D•O gives a linear relation down to 0.7X 10 -a. The mixtures show a linear relation above 1.5 X 10-a and a curvilinear approach to zero below that. Calculation indicates that the heterogeneous molecule HDO is far more effective as a thermal equilibrator for oxygen than either of its homogeneous parents. Quantitatively, with (f/p),,, in cps per atm and h in mole fraction X 10 a, the results are-100% H•O' (f/p),,,= 7 q-183hq-132h•-; 50% D•O' (f/p),•=--664q-llOOh; 80% D20' (f/p),•= --490q-908h; 92% D20' (f/p),,,= --250q-585h (above h= 1.3); 92% D•O' (f/p),•= 7q-275hq-100h•(below h= 1.3); 99.8% D•.O' (f/p),•=--85q-385h.
Using the pressure resonance tube developed in this laboratory, the relaxation frequency of oxygen has been measured as a function of water-vapor content, ranging from bone dry up through 140 ppm to 5500 ppm M. The mixture's composition, always at 100% relative humidity, was established by controlling the temperature and total pressure of oxygen in the tube, which always contained free water, or a water-glycerine mixture to reduce the vapor pressure. The relaxation frequency at one atmosphere is given in kc/sec⋅atm by f=0.003+1.66 h+14.5 h2, h, in mole percent. (Least-square solution, but the dry-oxygen relaxation frequency is actually 9 cps/atm.) This expression overlaps and extrapolates to fit the Knötzel's and Knudsen's data satisfactorily, but there is an outstanding discrepancy with the data for air of Evans and Bazley and of Harris, who used the reverberant-chamber method, and obtained a power law: e.g., f=kh1.6. The method of mixture control through total pressure is being extended to other volatile substances. [This work was supported by the U. S. Office of Naval Research under contract Nonr 2249(02).]
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