Generalized and Predictive Equations

Generalized and Predictive Equations.—Equations have so far been considered for fitting to experimentally observed values, but they will sometimes 

Reid and T. K. Sherwood, The Properties of Gases and Liquids, Their Estimation and Correlation , McGraw-Hill, New York, 2nd edn., 1966. 

Halm and L. I. Stiel, Amer. Inst. Chem. Engineers J., 1967,13, 351. 

Fitting of VapouT pressure Equations.—Useful advice on the graphical fitting of equations and simple evaluation of constants from selected points is given by Thomson, by Hdla et al., and by Miller. Least-squares treatment of the Antoine equation is described by Willingham et alJ The matter will not be pursued here since it is assumed that most fitting will be done today by computer, and the procedure cannot be covered usefully in a short account. One question which does need discussion however is that of weighting. 

In conclusion, the Reporter suggests to those who measure vapour pressures that, before publishing a set of values, they ought always to study the consistency of their measurements, both internally and with any others which have been published, because the job of the correlator who, in due course, will seek to produce a table of best values (or its equivalent equation) will then be made easier and his table of values will be more reliable. 

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