Hi INTRODUCTION. 



Table 68 is copied directly from Table 72. The argument is given for 

 every tenth of a degree from 8o-o to 100^9 C. The tabular values are given 

 to the nearest 0.01 mm. 



. 

 HYGROMETRICAL TABLES. 



PRESSURE OF SATURATED AQUEOUS VAPOR. 



In former editions of these tables the values of aqueous vapor pressures 

 at temperatures between — 29 and 100 C. were based upon Broch's re- 

 duction of the classic observations of Regnault. (Travaux et Memoir es 

 du Bureau international des Poids et Mesures, t. I, p. A 19-39). In these 

 computations the same continuous mathematical function was employed 

 to calculate the values of vapor pressure both above and below the point 

 of change of state on freezing. This resulted in a systematic disagreement 

 between observed and computed vapor pressures below the freezing point, 

 and confirmed the inference from the laws of diffusion following from the 

 kinetic theory of gases, namely, that the pressure of the vapor is different ac- 

 cording as it is in contact with its liquid or its solid. 



Seeking to remove the uncertainty of the values, of vapor pressures at 

 temperatures below freezing, Marvin (Annual Report Chief Signal Officer, 

 1 89 1, Appendix No. 10) made direct experimental determinations thereof, 

 in the course of which the specimens of water were cooled to temperatures 

 of from — io° to — 12 C. while still retaining the liquid state, thus af- 

 fording opportunity for measurements of vapor pressure over ice and over 

 water at various temperatures below the freezing point. The results of 

 these investigations, confirmed by similar independent studies by Juhlin, 

 were printed in the third revised edition of these tables. 



Since 1907, especially, several extended series x of entirely new deter- 

 minations, together covering the whole range of temperature from — 70 C. 

 to + 374 C, have been made at the Physikalische-Technischen Rcich- 

 sanstalt. Because of the elaborate instrumental means available and the 

 extreme effort to eliminate all possible errors these results may be presumed 

 to represent the most accurate series of experimental values of this impor- 

 tant physical datum available to science. 



Hitherto no satisfactory mathematical equation has been offered ade- 

 quate to give computed values of vapor pressures with an order of preci- 

 sion comparable to the systematic self consistency of the observations 



1 Scheel, Karl und Heuse, Wilhelm. Bestimmung des Sattigungsdrucks von Wasser- 

 dampf unter o°. Annalen der Physik, 1909, 29: 723-737. 



Bestimmung des Sattigungsdrucks von Wasserdampf zwischen o° und + 50 . Annalen 

 der Physik, 1910, 31: 715-736. 



Holborn, L. und Henning, F. t)ber das Platinthcrmometer und den Sattigungsdruck 

 des Wasserdampfes zwischen 50 und 200 . Annalen der Physik, 1908, 26: 833-883. 



Holborn, L. und Baumann, A. Ober den Sattigungsdruck des Wasserdampfes oberhalb 

 200°. Annalen der Physik, 1910, 31: 945-970. 



