Exp e rim e nt a l meas ure me nt s of th e e nh a nce m e nt factors fo r mi xtures of wa te r va iJor a nd C O ,· free a ir ha ve bee n made a t -20, -10 , a nd + 70°C. Th e res ult s. cou pled wit I. prev io us expe rim e nt a l e nh a nce· me nt data. ha ve b ee n use d 1.0 ca lc u la te th e seco nd int e rac ti o n viria l coe ffi " ie nt s. Bn".. fur wat e r vapur a ir mixture s from -50 to +90 °C. W ithin thi s te miJe ra tu re range. a n error ana lys is s hows th at th e un ce rt ai nti es in Bn"· are be t wee n 6 a nd ]0 iJe rCe nL Th e ca lc ul a ted Bn". va lues a re use d in d e rivin g e nh ance me nt fa c tors at ] 0 °C inte rval s for -50 < t < 90°C. a t varyin g press ure int e rva ls fn"n 0. 25 to 100 bar. Th e associate d un ce rtainties a re s hown as a fun c tiun of iJress ure a nd te mp e rature. Th e e nh a nce me nt fa c tors a re ex trapo la te d to -80°C.Key word s: Enhance ment factor; equ ation o f sta te; int e rac ti o n viria l cue fii cie nt s; mois t air; sa turated ai r; seco nd virial coe ffi c ie nt s; viria l co e ffi c ie nt s.
Th~ random (~ne standard deviation) uncertainty in the mean values of B aw, arising from the scatter of prevIOusly obtamed NBS values of the enhancement factor, is estimated to range from 0.7 percent a[ 30 ·C to 1.4 percent of 50°C. The estimated systematic uncertainties range from 4 percent at 30 °C to 6 percent at 50°C, respectively.
The enhancement of water vapor in compressed atmospheric air was measured at 30, 40, and 50°C over respective pressure ranges of 10 to 35 bars, 15 to 60 bars, and 10 to 100 bars. Th e data for each isotherm were fitted by the method of least squares to an empirical smoothing equation of the form In f = a+ bP where f is the enhanceme nt factor, P is the total (absolute) pressure and a and bare constants. A detailed error analysis , necessa ry for the event ual use of the data in humidity standards work , shows that the calculated (predicted) values of f have an estimated limit of sys temati c bias of ±0.07 percent and a maximum observed standard deviation of a predicted value of ±0.2 percent.Ke y words : Concentrati on of saturated water vapor in air; enha nce me nt fa ctor; moist air; moisture content of saturated air; saturated air; so lubility of water vapor in air; water vapor.
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