Ixvi INTRODUCTION 



TABLE 76. 



Table 76. Pressure of aqueous vapor over ice. Metric measures. 



The pressures, given to the nearest o.oooi mm., are computed by Nernst's 

 Formula (5), above, for each degree of temperature from —70° to —50° 

 inclusive, and by Thiesen's Formula (3), above, for each half degree from 



— 49?5 to —35° inclusive, and each tenth of a degree from — 36^0 to ±ofo. 



TABLE 77. 



Table 77. Pressure of aqueous vapor over water. Metric measures. 



The pressures, computed by equation (i) above, are given for each 

 tenth of a degree to o.ooi mm. from o?o to 59°9, and to o.oi mm. from 

 50°o to ioo?9. They are given for each degree to o.i mm. from 100° to 

 189°, and in millimeters from 190° to 374°. 



TABLE 78. 



Table 78. Pressure of aqueous vapor over ice. Dynamic measures. 



The pressures given in Table 78, in millibars, have been obtained by 

 multiplying the pressures given in Table 76, in millimeters, by 1.333224, the 

 value of one millimeter in millibars (see page xxii). The values are given for 

 each tenth of a degree between —70° C. and 0° C, inclusive. It may be noted 

 as in the case of Table 76 that the values between temperatures —50° C. 

 and — 70° C. inclusive have been obtained by means of the Nernst Formula 

 for the vapor pressure over ice (equation (5), p. Ixiv), whereas the values 

 between —50° C. and 0° C. have been obtained by means of the Thiesen 

 Formula (equation (3), p. Ixiv). Over the range of temperatures between 



— 50° C. and —36° C, the values for tenths of degrees have been obtained by 

 linear interpolation between whole degrees and half degrees. 



TABLE 79. 



Table 79. Pressure of aqueous vapor over water. Dynamic measures. 



Similarly, the vapor pressures in Table 79, in millibars, have been ob- 

 tained by multiplying the pressures given in Table yy by 1.333224, and are 

 given for each tenth of a degree between 0° C. and 44°9 C, inclusive. 



TABLES 80, 81. 



Table 80. Weight of a cubic foot of saturated aqueous vapor. English mea- 

 sures. 

 Table 81. Weight of a cubic meter of saturated aqueous vapor. Metric 

 measures. 

 For many years it has been customary to assume that the specific 

 gravity of water vapor relative to dry air is a constant whose theoretical 

 value computed from the accurately known densities of its constituent gases 

 is 0.6221. Direct experimental determinations of the specific volume of dry 

 saturated steam (as yet but few observations are available at moderate 

 temperatures) show conclusively (i) that this theoretical specific gravity is 

 true only for saturated vapor at very low temperatures or when the vapor 

 is in a very attenuated state of partial saturation; (2) that at increasingly 

 higher temperatures the specific gravity is increasingly greater than 0.6221. 

 These assertions are in accord with the values of w^eight per cubic foot of 



